LDC1101 1.8V 高分辨率、高速电感数字转换器
- ZHCSDS7A May 2015 – June 2015 LDC1101
  
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LDC1101 1.8V 高分辨率、高速电感数字转换器

本资源的原文使用英文撰写。为方便起见，TI 提供了译文；由于翻译过程中可能使用了自动化工具，TI 不保证译文的准确性。为确认准确性，请务必访问 ti.com 参考最新的英文版本（控制文档）。

1 特性

宽工作电压范围：1.8V 至 3.3V
传感器频率范围：500kHz 至 10MHz
R_P 分辨率：16 位
L 分辨率：16/24 位
180kSPS 转换速率
阈值检测功能
R_P 测量的器件间偏差为 1%
电源电流：
- 关断模式下为 1.4µA
- 休眠模式下为 135µA
- 激活模式下为 1.9mA（未连接传感器）
距离分辨率可达亚微米级
支持远程放置传感器，以便将 LDC 与恶劣环境隔离
可防水、油、污垢、灰尘等环境干扰
外部组件数极少
无磁体操作
工作温度范围：-40°C 至 125℃

2 应用

高速轮齿计数
高速事件计数
电机转速感测
家用电器、汽车和消费类应用中的旋钮和拨盘
家用电器、汽车和消费类应用中的人机界面 (HMI)
按钮和键盘
电机控制
金属探测

3 说明

LDC1101 是一款 1.8V 至 3.3V、高分辨率电感数字转换器，可对位置、旋转或运动进行短距离、高速、无触点感测，即使存在污垢或灰尘也能够实现可靠、精确的测量，非常适合户外或严苛环境。

LDC1101 特有双感应测量内核，可在执行 > 150ksps 的 16 位 R_P 和 L 测量的同时，进行分辨率高达 24 位的高分辨率 L 测量，采样速率可高达 180ksps 以上。 LDC1101 包含阈值比较功能，该功能可在器件运行时动态更新。

电感感测技术可实现对线性/角位置、位移、运动、压缩、振动、金属成分以及市面上包括汽车、消费类、计算机、工业、医疗和通信应用在内的很多其他应用的高精度测量。电感感测技术能够以低于其他竞争对手解决方案的成本提供更为出色的性能和可靠性。

LDC1101 在小型 3mm × 3mm 10 引脚 VSON 封装内即可提供这些电感感测技术优势。微控制器可使用 4 引脚 SPI™轻松配置 LDC1101。

器件信息⁽¹⁾

器件型号	封装	封装尺寸（标称值）
LDC1101	VSON (10)	3.00mm × 3.00mm

如需了解所有可用封装，请见数据表末尾的可订购产品附录。

4 简化电路原理图

LDC1101 simplified_schematic_snosd01.gif

5 修订历史记录

Changes from * Revision (May 2015) to A Revision

Added 完整数据表以替代产品预览Go

6 Pin Configuration and Functions

DRC Package

10-Pin VSON

Top View

Pin Functions

PIN		TYPE⁽¹⁾	DESCRIPTION
NAME	NO.	TYPE⁽¹⁾	DESCRIPTION
CLDO	10	P	Internal LDO bypassing pin. A 15 nF capacitor must be connected from this pin to GND.
CLKIN	2	I	External time-base Clock Input
CSB	5	I	SPI CSB. Multiple devices can be connected on the same SPI bus and CSB can be used to uniquely select desired device
DAP	–	–	Connect to Ground for improved thermal performance⁽²⁾
GND	8	G	Ground
INA	7	A	External LC tank – connected to external LC tank
INB	6	A	External LC tank – connected to external LC tank
SCLK	3	I	SPI Clock Input
SDI	4	I	SPI Data Input – connect to MOSI of SPI master
SDO/INTB	1	O	SPI Data Output/INTB – Connect to MISO of SPI Master. When CSB is high, this pin is High-Z. Alternatively, this pin can be configured to function as INTB
VDD	9	P	Power Supply

(1) P= Power, G=Ground, I=Input, O=Output, A=Analog

(2) There is an internal electrical connection between the exposed Die Attach Pad (DAP) and the GND pin of the device. Although the DAP can be left floating, for best performance the DAP should be connected to the same potential as the device's GND pin. Do not use the DAP as the primary ground for the device. The device GND pin must always be connected to ground.

7 Specifications

7.1 Absolute Maximum Ratings

over operating free-air temperature range (unless otherwise noted)⁽¹⁾

		MIN	MAX	UNIT
V_DD	Supply voltage range		3.6	V
V_i	Voltage on INA, INB	–0.3	2.3	V
V_i	Voltage on CLDO	–0.3	1.9	V
	Voltage on any other pin⁽²⁾	–0.3	V_DD+0.3	V
T_J	Junction temperature	–55	125	°C
T_stg	Storage temperature	–65	125	°C

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.

(2) Maximum voltage across any two pins is V_DD+0.3.

7.2 ESD Ratings

			VALUE	UNIT
V_(ESD)	Electrostatic discharge	Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001⁽¹⁾	±2000	V
V_(ESD)	Electrostatic discharge	Charged-device model (CDM), per JEDEC specification JESD22-C101⁽²⁾	±1000	V

(1) JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.

(2) JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.

7.3 Recommended Operating Conditions

over operating free-air temperature range (unless otherwise noted)

		MIN	NOM	MAX	UNIT
V_DD	Supply voltage	1.71		3.46	V
T_J	Junction temperature	–40		125	°C

7.4 Thermal Information

THERMAL METRIC⁽¹⁾		LDC1101	UNIT
		DRC (VSON)
		10 PINS
R_θJA	Junction-to-ambient thermal resistance	44.2	°C/W
R_θJC(top)	Junction-to-case (top) thermal resistance	50.1	°C/W
R_θJB	Junction-to-board thermal resistance	19.6	°C/W
ψ_JT	Junction-to-top characterization parameter	0.7	°C/W
ψ_JB	Junction-to-board characterization parameter	19.8	°C/W
R_θJC(bot)	Junction-to-case (bottom) thermal resistance	4.4	°C/W

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application report, SPRA953.

7.5 Electrical Characteristics

Over recommended operating conditions unless otherwise noted. V_DD= 1.8 V, T_A = 25°C.

PARAMETER		TEST CONDITION⁽¹⁾	MIN⁽²⁾	TYP⁽³⁾	MAX⁽²⁾	UNIT
POWER
V_DD	Supply voltage		1.71		3.46	V
I_DD	Supply current	START_CONFIG= 0x00, no sensor connected		1.9	2.7	mA
I_DDS	Supply current including sensor current	ƒ_CLKIN = 16 MHz, ƒ_SENSOR = 2 MHz, START_CONFIG = 0x00		3.2		mA
I_DDSL	Sleep mode supply current	START_CONFIG =0x01		135	180	µA
I_SD	Shutdown mode supply current			1.4	6.7	µA
SENSOR
	R_P Measurement part-to-part variation	RESP_TIME= 6144, D_CONFIG=0x00, ALT_CONFIG=0x00, START_CONFIG = 0x00, ƒ_SENSOR = 2 MHz		1%
I_SENSORMAX	Sensor maximum current drive	RP_MIN = b111, START_CONFIG=0x00, D_CONFIG=0x00, ALT_CONFIG=0x00	0.598	0.6	0.602	mA
I_SENSORMIN	Sensor minimum current drive	RP_MAX = b000, RPMAX_DIS=b0, START_CONFIG=0x00, D_CONFIG=0x00, ALT_CONFIG=0x00		4.7		µA
ƒ_SENSOR	Sensor resonant frequency	Device settings and Sensor compliant as detailed in LDC1101 RP Configuration	0.5		10	MHz
RP_RES	R_P Measurement resolution			16		bits
L_RES	Inductance sensing resolution – R_P+L Mode			16		bits
L_RES	Inductance sensing resolution – LHR Mode			24		bits
A_OSC	Sensor oscillation amplitude	INA – INB, START_CONFIG=0x00, D_CONFIG=0x00, ALT_CONFIG=0x00		1.2		V_PP
DETECTION
t_{S_MIN}	Minimum response time (RP+L mode)	R_P+L Mode, RESP_TIME=b010		192 ÷ƒ_SENSOR		s
t_{S_MAX}	Maximum response time (RP+L mode)	R_P+L Mode, RESP_TIME=b111		6144 ÷ƒ_SENSOR		s
T_{s_MAX}	High Res L maximum measurement interval	LHR_REF_COUNT=0xFFFF, START_CONFIG=0x00		(2²⁰+39) ÷ƒ_CLKIN		s
SR_MAXRP	RP+L Mode maximum sample rate	ƒ_CLKIN=16 MHz, ƒ_SENSOR = 10 MHz, RESP_TIME=b010		156.25		kSPS
S_RMAXL	High Res L Mode Maximum Sample Rate	High Resolution L Mode, LHR_REF_COUNT=0x0002, ƒ_CLKIN=16 MHz		183.8		kSPS
FREQUENCY REFERENCE
f_CLKIN	Reference input frequency		1		16	MHz
DC_fin	Reference duty cycle		40%		60%
V_IH	Input high voltage (Logic “1”)			0.8×V_DD		V
V_IL	Input low voltage (Logic “0”)			0.2×V_DD		V

(1) Register values are represented as either binary (b is the prefix to the digits), or hexadecimal (0x is the prefix to the digits). Decimal values have no prefix.

(2) Limits are ensured by testing, design, or statistical analysis at 25°C. Limits over the operating temperature range are ensured through correlation using statistical quality control (SQC) method.

(3) Typical values represent the most likely parametric norm as determined at the time of characterization. Actual typical values may vary over time and will also depend on the application and configuration. The typical values are not tested and are not guaranteed on shipped production material.

7.6 Digital Interface

PARAMETER		MIN	TYP	MAX	UNIT
VOLTAGE LEVELS		0.8×V_DD			V
V_IH	Input high voltage (Logic “1”)			0.2×V_DD	V
V_IL	Input low voltage (Logic “0”)		V_DD–0.3		V
V_OH	Output high voltage (Logic “1”, I_SOURCE = 400 µA)			0.3	V
V_OL	Output low voltage (Logic “0”, I_SINK = 400 µA)	–500		500	nA
I_OHL	Digital IO leakage current

7.7 Timing Requirements

		MIN	TYP	MAX	UNIT
t_START	Start-up time from shutdown to sleep		0.8		ms
t_WAKE	Wake-up time (from completion of SPI to conversion start; does not include sensor settling time)		0.04		ms
INTERFACE TIMING REQUIREMENTS⁽¹⁾
ƒ_SCLK	Serial clock frequency			8	MHz
t_wH	SCLK pulse-width high	0.4 / ƒ_SCLK			s
t_wL	SCLK pulse-width low	0.4 / ƒ_SCLK			s
t_su	SDI setup time	10			ns
t_h	SDI hold time	10			ns
t_ODZ	SDO driven-to-tristate time			25	ns
t_OZD	SDO tristate-to-driven time			25	ns
t_OD	SDO output delay time			20	ns
t_su(CS)	CSB setup time	20			ns
t_h(CS)	CSB hold time	20			ns
t_IAG	CSB inter-access interval	100			ns
t_w(DRDY)	Data ready pulse width		1/ƒ_SENSOR		ns

(1) Unless otherwise noted, all limits specified at T_A = 25°C, V_DD = 1.8 V, 10 pF capacitive load in parallel with a 10 kΩ load on the SDO pin. Specified by design; not production tested.

LDC1101 write_timing_diagram_snosd01.gif

Figure 1. Write Timing Diagram

Figure 2. Read Timing Diagram

7.8 Typical Characteristics

LDC1101 D001_idd_vs_temperature_SNOSD01.gif

Not including sensor current, default register settings.

Figure 3. I_DD vs Temperature

LDC1101 D003_supply_current_vs_fclkin_SNOSD01.gif

Including sensor current. 13mm diameter sensor 0.1mm spacing/0.1mm trace width/ 4 layer 28 turns, f_SENSOR = 2 MHz, RP_SET = 0x07, TX1=0x50, TC2=0x80, RCOUNT=0xFFFF, RESP_TIME =6144

Figure 5. Supply Current (mA) vs ƒ_CLKIN (MHz) at 25°C

LDC1101 D005_idd_sleep_mode_vs_vdd_SNOSD01.gif

Figure 7. I_DDSleep Mode vs V_DD

LDC1101 D007_idd_shutdown_vs_vdd_SNOSD01.gif

Figure 9. I_DD Shutdown vs V_DD

LDC1101 D009_isensormin_vs_vdd_SNOSD01.gif

RP_SET.RPMAX = b000

Figure 11. I_SENSOR-MIN vs V_DD

Not including sensor current, default register settings.

Figure 4. I_DD vs V_DD

LDC1101 D004_idd_sleep_mode_vs_temperature_SNOSD01.gif

Figure 6. I_DD Sleep Mode vs Temperature

LDC1101 D006_idd_shutdown_vs_temperature_SNOSD01.gif

Figure 8. I_DD Shutdown vs Temperature

LDC1101 D008_isensormax_vs_vdd_SNOSD01.gif

RP_SET.RPMIN = b111

Figure 10. I_SENSOR-MAX vs V_DD

8 Detailed Description

8.1 Overview

The LDC1101 is an inductance-to-digital converter which can simultaneously measure the impedance and resonant frequency of an LC resonator. The high resolution measurement capability enables this device to be used to directly measure changes in physical systems, allowing the resonator to sense the proximity and movement of conductive materials.

The LDC1101 measures the impedance and resonant frequency by regulating the oscillation amplitude in a closed-loop configuration at a constant level, while monitoring the energy dissipated by the resonator. By monitoring the amount of power injected into the resonator, the LDC1101 can determine the equivalent parallel resistance of the resonator, R_P, which it returns as a digital value.

In addition, the LDC1101 device also measures the oscillation frequency of the LC circuit by comparing the sensor frequency to a provided reference frequency. The sensor frequency can then be used to determine the inductance of the LC circuit.

The threshold comparator block can compare the RP+L conversion results versus a programmable threshold. With the threshold registers programmed and comparator enabled, the LDC1101 can provide a switch output, reported as a high/low level on the INTB/SDO pin.

The LDC1101 device supports a wide range of LC combinations with oscillation frequencies ranging from 500 kHz to 10 MHz and R_P ranging from 1.25 kΩ to 90 kΩ. The device is configured and conversion results retrieved through a simple 4-wire SPI. The power supply for the device can range from 1.8 V – 5% to 3.3 V + 5%. The only external components necessary for operation are a 15 nF capacitor for internal LDO bypassing and supply bypassing for VDD.

8.2 Functional Block Diagram

LDC1101 ldc1101_block_diagram_snosd01.gif

8.3 Feature Description

8.3.1 Sensor Driver

The LDC1101 can drive a sensor with a resonant frequency of 500 kHz to 10 MHz with an R_P in the range of 1.25 kΩ to 90 kΩ. The nominal sensor amplitude is 1.2 V. The sensor Q should be at least 10 for R_P measurements. The inductive sensor must be connected across the INA and INB pins. The resonant frequency of the sensor is set by:

Equation 1. LDC1101 Eq01_fsensor_snosd01.gif

where

L is the sensor inductance in Henrys, and
C is the sensor parallel capacitance in Farads.

8.4 Device Functional Modes

8.4.1 Measurement Modes

The LDC1101 features two independent measurement subsystems to measure the impedance and resonant frequency of an attached sensor. The R_P+L subsystem can simultaneously measure the impedance and resonant frequency of an LC resonator, with up to 16 bits of resolution for each parameter. Refer to RP+L Measurement Mode for more information on the R_P+L measurement functionality.

The High Resolution L (LHR) subsystem measures the sensor resonant frequency with up to 24 bits of resolution. The effective resolution is a function of the sample rate and the reference frequency supplied on the CLKIN pin. Refer to High Resolution L (LHR) Measurement Mode for more information on the LHR measurement functionality.

Both measurement subsystems can convert simultaneously but at different sample intervals – the completion of an R_P+L conversion will be asynchronous to the completion of a LHR conversion.

Table 1. Comparison of Measurement Modes

	RP+L Mode	LHR Mode
R_P Measurement Resolution	16 bits	N/A
L Measurement Resolution	16 bits	24 bits
Sample Rate configuration	Varies with ƒ_SENSOR, set by RESP_TIME	Fixed and set by RCOUNT field and ƒ_CLKIN
Sample rate at highest resolution (SPS)	244	15.3
Maximum Sample Rate (kSPS)	156.25	183.9
L Resolution at Maximum Sample rate	6.7 bits	6.5 bits
Switch Output on SDO/INTB	Available for R_P or L output code	N/A

8.4.2 R_P+L Measurement Mode

In RP+L mode, the LDC1101 will simultaneously measure the impedance and resonant frequency of the attached sensor. The device accomplishes this task by regulating the oscillation amplitude in a closed-loop configuration to a constant level, while monitoring the energy dissipated by the resonator. By monitoring the amount of power injected into the resonator, the LDC1101 device can determine the value of R_P. The device returns this value as a digital value which is proportional to R_P. In addition, the LDC1101 device can also measure the oscillation frequency of the LC circuit, by counting the number of cycles of a reference frequency. The measured sensor frequency can be used to determine the inductance of the LC circuit.

8.4.2.1 RPMIN and RPMAX

The variation of R_P in a given system is typically much smaller than maximum range of 1.25 kΩ to >90 kΩ supported by the LDC1101. To achieve better resolution for systems with smaller R_P ranges, the LDC1101 device offers a programmable R_P range.

The LDC1101 uses adjustable current drives to scale the R_P measurement range; by setting a tighter current range a higher accuracy R_P measurement can be performed. This functionality can be considered as a variable gain amplifier (VGA) front end to an ADC. The current ranges are configured in the RPMIN and RPMAX fields of register RP_SET (address 0x01). Refer to LDC1101 RP Configuration for instructions to optimize these settings.

8.4.2.2 Programmable Internal Time Constants

The LDC1101 utilizes internal programmable registers to configure time constants necessary for sensor oscillation. These internal time constants must be configured for R_P measurements. Refer to Setting Internal Time Constant 1 and Setting Internal Time Constant 2 for instructions on how to configure them for a given system.

8.4.2.3 R_P+L Mode Measurement Sample Rate

The LDC1101 provides an adjustable sample rate for the RP+L conversion, where longer conversion times have higher resolution. Refer to RP+L Sample Rate Configuration with RESP_TIME for more details.

8.4.3 High Resolution L (LHR) Measurement Mode

The High Resolution L measurement (LHR) subsystem provides a high-resolution inductance (L) measurement of up to 24 bits. This L measurement can be configured to provide a higher resolution measurement than the measurement returned from the RP+L subsystem. The LHR subsystem also provides a constant conversion time interval, whereas the RP+L conversion interval is a function of the sensor frequency. The LHR measurement runs asynchronously with respect to the RP+L measurement.

8.4.4 Reference Count Setting

The LHR sample rate is set by the Reference Count (LHR_RCOUNT) setting (registers 0x30 and 0x31). The LHR conversion resolution is proportional to the programmed RCOUNT value. With the maximum supported 16 MHz CLKIN input, the LDC1101 conversion interval can be set from 8.6 µs to 87.38 ms in 1 µs increments. Note that longer conversion intervals produce more accurate LHR measurements. Refer to LHR Sample Rate Configuration with RCOUNT for more details.

8.4.5 L-Only Measurement Operation

The LDC1101 can disable the R_P measurement to perform a more stable L measurement. To enable this mode, set:

ALT_CONFIG.LOPTIMAL(register 0x05-bit0) = 1
D_CONFIG.DOK_REPORT (register 0x0C-bit0) = 1

When this mode is used, R_P measurement results are not valid.

8.4.6 Minimum Sensor Frequency and Watchdog Setting

The LDC1101 can report an error condition if the sensor oscillation stops. Refer to MIN_FREQ and Watchdog Configuration for information on the configuration of the watchdog.

8.4.7 Low Power Modes

When continuous LDC conversions are not required, the LDC1101 supports two reduced power modes. In Sleep mode, the LDC1101 retains register settings and can quickly enter active mode for conversions. In Shutdown mode, power consumption is significantly lower, although the device configuration is not retained. While in either low power mode, the LDC1101 will not perform conversions.

8.4.7.1 Shutdown Mode

Shutdown mode is the lowest power state for the LDC1101. Note that entering SD mode will reset all registers to their default state, and so the device must have its registers rewritten. To enter Shutdown, perform the following sequence:

Set ALT_CONFIG.SHUTDOWN_EN = 1 (register 0x05-bit[1]).
Stop toggling the CLKIN pin input and drive the CLKIN pin Low.
Set START_CONFIG.FUNC_MODE = b10 (register 0x0B:bits[1:0]). This register can be written while the LDC1101 is in active mode; on completion of the register write the LDC1101 will enter shutdown.

To exit Shutdown mode, resume toggling the clock input on the CLKIN pin; the LDC1101 will transition to Sleep mode with the default register values.

While in Shutdown mode, no conversions are performed. In addition, entering Shutdown mode will clear the status registers; if an error condition is present it will not be reported when the device exits Shutdown mode.

8.4.7.2 Sleep Mode

Sleep mode is entered by setting START_CONFIG.FUNC_MODE =b01 (register 0x0B:bits[1:0]). While in this mode, the register contents are maintained. To exit Sleep mode and start active conversions, set START_CONFIG.FUNC_MODE = b00. While in Sleep mode the SPI interface is functional so that register reads and writes can be performed.

On power-up or exiting Shutdown mode, the LDC1101 will be in Sleep mode.

Configuring the LDC1101 must be done while the device is in Sleep mode. If a setting on the LDC1101 needs to be changed, return the device to Sleep mode, change the appropriate register, and then return the LDC1101 to conversion mode. The registers related to INTB reporting can be changed while the LDC1101 is in active mode. Refer to INTB Reporting on SDO for more details.

8.4.8 Status Reporting

The LDC1101 provides 2 status registers, STATUS and LHR_STATUS, to report on the device and sensor condition.

Table 2. STATUS Fields

NAME	FIELD	FUNCTION
NO_SENSOR_OSC	7	When the resonance impedance of the sensor, R_P, drops below the programed Rp_MIN, the sensor oscillation may stop. This condition is reported by STATUS:NO_SENSOR_OSC (register 0x20-bit7). This condition could occur when a target comes too close to the sensor or if RP_SET:RP_MIN (register 0x01-bits[2:0]) is set too high.
DRDYB	6	RP+L Data Ready - reports completion of RP+L conversion results
RP_HIN	5	RP+L threshold – refer to Comparator Functionalityfor details
RP_HI_LON	4
L_HIN	3
L_HI_LON	2
POR_READ	0	Device in Power-On Reset – device should only be configured when POR_READ = 0.

The LHR_STATUS register (register 0x3B) reports on LHR functionality.

8.4.9 Switch Functionality and INTB Reporting

The SDO pin can generate INTB, a signal which corresponds to device status. INTB can report conversion completion or provide a comparator output, in which the LDC conversion results are internally compared to programmable thresholds. Refer to INTB Reporting on SDO for details.

8.5 Programming

8.5.1 SPI Programming

The LDC1101 uses SPI to configure the internal registers. It is necessary to configure the LDC1101 while in Sleep mode. If a setting on the LDC1101 needs to be changed, return the device to Sleep mode, change the appropriate register, and then return the LDC1101 to conversion mode. CSB must go low before accessing first address. If the number of SCLK pulses is less than 16, a register write command will not change the contents of the addressed register.

LDC1101 spi_transaction_format_snosd01.gif

Figure 12. SPI Transaction Format

The LDC1101 supports an extended SPI transaction, in which CSB is held low and sequential register addresses can be written or read. After the first register transaction, each additional 8 SCLK pulses will address the next register, reading or writing based on the initial R/W flag in the initial command. A register write command will take effect on the 8th clock pulse. Two or more registers can be programmed using this method. The register address must not increment above 0x3F.

LDC1101 extended_spi_transaction_snosd01.gif

Figure 13. Extended SPI Transaction

8.6 Register Maps

Table 3. Register List

ADDRESS	NAME	DEFAULT VALUE	DESCRIPTION
0x01	RP_SET	0x07	Configure R_P Measurement Dynamic Range
0x02	TC1	0x90	Configure Internal Time Constant 1
0x03	TC2	0xA0	Configure Internal Time Constant 2
0x04	DIG_CONFIG	0x03	Configure RP+L conversion interval
0x05	ALT_CONFIG	0x00	Configure additional device settings
0x06	RP_THRESH_H_LSB	0x00	RP_THRESHOLD High Setting – bits 7:0. This register can be modified while the LDC1101 is in active mode.
0x07	RP_THRESH_H_MSB	0x00	RP_THRESHOLD High Setting – bits 15:8. This register can be modified while the LDC1101 is in active mode.
0x08	RP_THRESH_L_LSB	0x00	RP_THRESHOLD Low Setting – bits 7:0. This register can be modified while the LDC1101 is in active mode.
0x09	RP_THRESH_L_MSB	0x00	RP_THRESHOLD Low Setting – bits 15:8. This register can be modified while the LDC1101 is in active mode.
0x0A	INTB_MODE	0x00	Configure INTB reporting on SDO pin. This register can be modified while the LDC1101 is in active mode.
0x0B	START_CONFIG	0x01	Configure Power State
0x0C	D_CONF	0x00	Sensor Amplitude Control Requirement
0x16	L_THRESH_HI_LSB	0x00	L_THRESHOLD High Setting – bits 7:0. This register can be modified while the LDC1101 is in active mode.
0x17	L_THRESH_HI_MSB	0x00	L_THRESHOLD High Setting – bits 15:8. This register can be modified while the LDC1101 is in active mode.
0x18	L_THRESH_LO_LSB	0x00	L_THRESHOLD Low Setting – bits 7:0. This register can be modified while the LDC1101 is in active mode.
0x19	L_THRESH_LO_MSB	0x00	L_THRESHOLD Low Setting – bits 15:8. This register can be modified while the LDC1101 is in active mode.
0x20	STATUS	0x00	Report RP+L measurement status
0x21	RP_DATA_LSB	0x00	R_P Conversion Result Data Output - bits 7:0
0x22	RP_DATA_MSB	0x00	R_P Conversion Result Data Output - bits 15:8
0x23	L_DATA_LSB	0x00	L Conversion Result Data Output - bits 7:0
0x24	L_DATA_MSB	0x00	L Conversion Result Data Output - bits 15:8
0x30	LHR_RCOUNT_LSB	0x00	High Resolution L Reference Count – bits 7:0
0x31	LHR_RCOUNT_MSB	0x00	High Resolution L Reference Count – bits 15:8
0x32	LHR_OFFSET_LSB	0x00	High Resolution L Offset – bits 7:0
0x33	LHR_OFFSET_MSB	0x00	High Resolution L Offset – bits 15:8
0x34	LHR_CONFIG	0x00	High Resolution L Configuration
0x38	LHR_DATA_LSB	0x00	High Resolution L Conversion Result Data output - bits 7:0
0x39	LHR_DATA_MID	0x00	High Resolution L Conversion Result Data output - bits 15:8
0x3A	LHR_DATA_MSB	0x00	High Resolution L Conversion Result Data output - bits 23:16
0x3B	LHR_STATUS	0x00	High Resolution L Measurement Status
0x3E	RID	0x02	Device RID value
0x3F	CHIP_ID	0xD4	Device ID value

8.6.1 Individual Register Listings

Fields indicated with Reserved must be written only with indicated values. Improper device operation may occur otherwise. The R/W column indicates the Read-Write status of the corresponding field. A ‘R/W’ entry indicates read and write capability, a ‘R’ indicates read-only, and a ‘W’ indicates write-only.

8.6.2 Register RP_SET (address = 0x01) [reset = 0x07]

Figure 14. Register RP_SET

7	6	5	4	3	2	1	0
RPMAX_DIS	RP_MAX			RESERVED	RP_MIN
R/W	R/W			R/W	R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 4. Register RP_SET Field Descriptions

Bit	Field	Type	Description
7	RPMAX_DIS	R/W	RP_MAX Disable This setting improves the R_P measurement accuracy for very high Q coils by driving 0A as the R_PMAX current drive. b0: Programmed RP_MAX is driven (default value) b1: RP_MAX current is ignored; current drive is off.
6:4	RP_MAX	R/W	RP_MAX Setting Set the maximum input dynamic range for the sensor R_P measurement. The programmed RP_MIN setting must not exceed the programmed RP_MAX setting. b000: RPMAX = 96 kΩ (default value) b001: RPMAX = 48 kΩ b010: RPMAX = 24 kΩ b011: RPMAX = 12 kΩ b100: RPMAX = 6 kΩ b101: RPMAX = 3 kΩ b110: RPMAX = 1.5 kΩ b111: RPMAX = 0.75 kΩ
3	RESERVED	R/W	Reserved. Set to 0
2:0	RP_MIN	R/W	RP_MIN Setting Set the minimum input dynamic range for the sensor R_P measurement. The programmed RP_MIN setting must not exceed the programmed RP_MAX setting. b000: RPMIN = 96 kΩ b001: RPMIN = 48 kΩ b010: RPMIN = 24 kΩ b011: RPMIN = 12 kΩ b100: RPMIN = 6 kΩ b101: RPMIN = 3 kΩ b110: RPMIN = 1.5 kΩ b111: RPMIN = 0.75 kΩ (default value)

8.6.3 Register TC1 (address = 0x02) [reset = 0x90]

Figure 15. Register TC1

7	6	5	4	3	2	1	0
C1		RESERVED	R1
R/W		R/W	R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 5. Register TC1 Field Descriptions

Bit	Field	Type	Description
7:6	C1	R/W	Internal Time Constant 1 Capacitance This sets the capacitive component used to configure internal time constant 1. Refer to Setting Internal Time Constant 1 for more details. b00: C1 = 0.75 pF b01: C1 = 1.5 pF b10: C1 = 3.0 pF (default value) b11: C1 = 6.0 pF
5	RESERVED	R/W	Reserved. Set to 0
4:0	R1	R/W	Internal Time Constant 1 Resistance This sets the resistive component used to configure internal time constant 1. Refer to Setting Internal Time Constant 1 for configuration details. R1(Ω) = -12.77 kΩ × R1 + 417 kΩ Valid Values: [b0’0000:b1’1111] b0’0000: R₁ = 417 kΩ b1’0000: R₁ = 212.7kΩ (default value) b1’1111: R₁ = 21.1 kΩ

Bit

Field

Type

Reset

Description

7:6

R/W

Internal Time Constant 1 Capacitance

This sets the capacitive component used to configure internal time constant 1. Refer to Setting Internal Time Constant 1 for more details.

b00: C1 = 0.75 pF
b01: C1 = 1.5 pF
b10: C1 = 3.0 pF (default value)
b11: C1 = 6.0 pF

RESERVED

R/W

Reserved. Set to 0

4:0

R/W

Internal Time Constant 1 Resistance

This sets the resistive component used to configure internal time constant 1. Refer to Setting Internal Time Constant 1 for configuration details.

R1(Ω) = -12.77 kΩ × R1 + 417 kΩ

Valid Values: [b0’0000:b1’1111]
b0’0000: R₁ = 417 kΩ
b1’0000: R₁ = 212.7kΩ (default value)
b1’1111: R₁ = 21.1 kΩ

8.6.4 Register TC2 (address = 0x03) [reset = 0xA0]

Figure 16. Register TC2

7	6	5	4	3	2	1	0
C2		R2
R/W		R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 6. Register TC2 Field Descriptions

Bit	Field	Type	Reset	Description
7:6	C2	R/W		Internal Time Constant 2 Capacitance This sets the capacitive component used to configure internal time constant 2. Refer to Setting Internal Time Constant 2 for configuration details. b00: C2 = 3 pF b01: C2 = 6 pF b10: C2 = 12 pF (default value) b11: C2 = 24 pF
5:0	R2	R/W		Internal Time Constant 2 Resistance This sets the resistive component used to configure internal time constant 2. Refer to Setting Internal Time Constant 2for details. R2(Ω) = -12.77 kΩ × R2 + 835 kΩ Valid Values: [b00’0000:b11’1111] b00’0000: R₂ = 835kΩ b10’0000: R₂ = 426.4 kΩ (default value) b11’1111: R₂ = 30.5 kΩ

8.6.5 Register DIG_CONF (address = 0x04) [reset = 0x03]

Figure 17. Register DIG_CONF

7	6	5	4	3	2	1	0
MIN_FREQ				RESERVED	RESP_TIME
R/W				R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 7. Register DIG_CONF Field Descriptions

Bit	Field	Type	Description
7:4	MIN_FREQ	R/W	Sensor Minimum Frequency Configure this register based on the lowest possible sensor frequency. This is typically when the target is providing minimum interaction with the sensor, although with some steel and ferrite targets, the minimum sensor frequency occurs with maximum target interaction. This setting should include any additional effects which reduce the sensor frequency, including temperature shifts and sensor capacitor variation. MIN_FREQ = 16 – (8 MHz ÷ ƒ_SENSORMIN) b0000: ƒ_SENSORMIN = 500 kHz (default value) b1111: ƒ_SENSORMIN = 8 MHz
3	RESERVED	R/W	Reserved. Set to 0
2:0	RESP_TIME	R/W	Measurement Response Time Setting Sets the Response Time, which is the number of sensor periods used per conversion. This setting applies to the R_P and Standard Resolution L measurement, but not the High Resolution L measurement. This corresponds to the actual conversion time by: b000: Reserved (do not use) b001: Reserved (do not use) b010: Response Time = 192 b011: Response Time = 384 (default value) b100: Response Time = 768 b101: Response Time = 1536 b110: Response Time = 3072 b111: Response Time = 6144

Bit

Field

Type

Reset

Description

7:4

MIN_FREQ

R/W

Sensor Minimum Frequency

Configure this register based on the lowest possible sensor frequency. This is typically when the target is providing minimum interaction with the sensor, although with some steel and ferrite targets, the minimum sensor frequency occurs with maximum target interaction.

This setting should include any additional effects which reduce the sensor frequency, including temperature shifts and sensor capacitor variation.

MIN_FREQ = 16 – (8 MHz ÷ ƒ_SENSORMIN)

b0000: ƒ_SENSORMIN = 500 kHz (default value)
b1111: ƒ_SENSORMIN = 8 MHz

RESERVED

R/W

Reserved. Set to 0

2:0

RESP_TIME

R/W

Measurement Response Time Setting

Sets the Response Time, which is the number of sensor periods used per conversion. This setting applies to the R_P and Standard Resolution L measurement, but not the High Resolution L measurement. This corresponds to the actual conversion time by:

b000: Reserved (do not use)
b001: Reserved (do not use)
b010: Response Time = 192
b011: Response Time = 384 (default value)
b100: Response Time = 768
b101: Response Time = 1536
b110: Response Time = 3072
b111: Response Time = 6144

8.6.6 Register ALT_CONFIG (address = 0x05) [reset = 0x00]

Figure 18. Register ALT_CONFIG

7	6	5	4	3	2	1	0
RESERVED						SHUTDOWN_EN	LOPTIMAL
R/W						R/W	R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 8. Register ALT_CONFIG Field Descriptions

Bit	Field	Type	Description
7:2	RESERVED	R/W	Reserved. Set to b00'0000.
1	SHUTDOWN_EN	R/W	Shutdown Enable Enables shutdown mode of operation. If SHUTDOWN_EN is not set to 1, then SHUTDOWN (Address 0x0B:[1]) will not have any effect. b0: Shutdown not enabled. (default value) b1: Shutdown functionality enabled.
0	LOPTIMAL	R/W	Optimize for L Measurements Optimize sensor drive signal for L measurements (for both High-Res L and L measurement). When LOPTIMAL is enabled, R_P measurements will not be completed. It is also necessary to set DOK_REPORT=1 when this mode is enabled. b0: L optimal disabled; both RP+L/LHR measurements (default value) b1: Only perform LHR and/or L-only measurements. R_P measurements are invalid.

8.6.7 Register RP_THRESH_HI_LSB (address = 0x06) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 19. Register RP_THRESH_HI_LSB

7	6	5	4	3	2	1	0
RP_THRESH_HI_LSB
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 9. Register RP_THRESH_HI_LSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RP_THRESH_HI_LSB	R/W		R_P High Threshold LSBSetting Combine with value in Register RP_THRESH_HI_MSB (Address 0x07) to set the upper R_P conversion threshold: RP_THRESH_HI = RP_THRESH_HI[15:8] × 256 + RP_THRESH_HI[7:0] If RP_DATA conversion result is greater than the RP_THRESH_HI, RP_TH_I will be asserted. Note that RP_THRESH_HI_LSB is buffered and will not change the device configuration until a write to RP_TRESH_HI_MSB is performed. Note that both registers 0x06 and 0x07 must be written to change the value of RP_THRESH_HI. 0x00: default value

Bit

Field

Type

Reset

Description

7:0

RP_THRESH_HI_LSB

R/W

R_P High Threshold LSBSetting

Combine with value in Register RP_THRESH_HI_MSB (Address 0x07) to set the upper R_P conversion threshold:

RP_THRESH_HI = RP_THRESH_HI[15:8] × 256 + RP_THRESH_HI[7:0]

If RP_DATA conversion result is greater than the RP_THRESH_HI, RP_TH_I will be asserted.

Note that RP_THRESH_HI_LSB is buffered and will not change the device configuration until a write to RP_TRESH_HI_MSB is performed. Note that both registers 0x06 and 0x07 must be written to change the value of RP_THRESH_HI.

0x00: default value

8.6.8 Register RP_THRESH_HI_MSB (address = 0x07) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 20. Register RP_THRESH_HI_MSB

7	6	5	4	3	2	1	0
RP_THRESH_HI_MSB
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 10. Register RP_THRESH_HI_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RP_THRESH_HI_MSB	R/W		R_P High Threshold MSB Setting Combine with value in Register RP_THRESH_HI_LSB (Address 0x06) to set the upper R_P conversion threshold. 0x00: default value

8.6.9 Register RP_THRESH_LO_LSB (address = 0x08) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 21. Register RP_THRESH_LO_LSB

7	6	5	4	3	2	1	0
RP_THRESH_LO_LSB
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 11. Register RP_THRESH_LO_LSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RP_THRESH_LO[7:0]	R/W		R_P Low Threshold LSB Setting Combine with value in Register RP_THRESH_LO_MSB (Address 0x09) to set the lower R_P conversion threshold: RP_THRESH_LO = RP_THRESH_LO[15:8] ×256 + RP_THRESH_LO[7:0] If RP_DATA conversion result is less than the RP_THRESH_LO, RP_HI_LON will be asserted. Note that RP_THRESH_LO_LSB is buffered and will not change the device configuration until a write to RP_TRESH_LO_MSB is performed. Note that both registers 0x08 and 0x09 must be written to change the value of RP_THRESH_LO. 0x00: default value

Bit

Field

Type

Reset

Description

7:0

RP_THRESH_LO[7:0]

R/W

R_P Low Threshold LSB Setting

Combine with value in Register RP_THRESH_LO_MSB (Address 0x09) to set the lower R_P conversion threshold:

RP_THRESH_LO = RP_THRESH_LO[15:8] ×256 + RP_THRESH_LO[7:0]

If RP_DATA conversion result is less than the RP_THRESH_LO, RP_HI_LON will be asserted. Note that RP_THRESH_LO_LSB is buffered and will not change the device configuration until a write to RP_TRESH_LO_MSB is performed.

Note that both registers 0x08 and 0x09 must be written to change the value of RP_THRESH_LO.

0x00: default value

8.6.10 Register RP_THRESH_LO_MSB (address = 0x09) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode

Figure 22. Register RP_THRESH_LO_MSB

7	6	5	4	3	2	1	0
RP_THRESH_LO_MSB
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 12. Register RP_THRESH_LO_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RP_THRESH_LO_MSB[15:8]	R/W		R_P Low Threshold MSB Setting Combine with value in Register RP_THRESH_LO_LSB (Address 0x08) to set the lower R_P conversion threshold. 0x00: default value

8.6.11 Register INTB_MODE (address = 0x0A) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 23. Register INTB_MODE

7	6	5	4	3	2	1	0
INTB2SDO	RESERVED	INTB_FUNC
R/W	R/W	R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 13. NAME Field Descriptions

Bit	Field	Type	Description
7	INTB2SDO	R/W	INTB Output on SDO Output INTB signal on SDO pin. b0: do not report DRDY on SDO pin (default value) b1: report DRDY on SDO pin
6	RESERVED	R/W	Reserved. Set to 0
5:0	INTB_FUNC	R/W	Select INTB signal reporting. INTB2SDO must be set to 1 for the selected signal to appear on the SDO pin. Refer to INTB Reporting on SDO for configuration details. b10’0000: Report LHR Data Ready b01’0000: Compare L conversion to L Thresholds (hysteresis) b00’1000: Compare L conversion to L High Threshold (latching) b00’0100: Report RP+L Data Ready b00’0010: Compare R_P conversion to R_P Thresholds (hysteresis) b00’0001: Compare R_P conversion to R_P High Threshold (latching) b00’0000: no output (default value) All other values: Reserved

8.6.12 9.Register START_CONFIG (address = 0x0B) [reset = 0x01]

This register can be modified while the LDC1101 is in active mode.

Figure 24. Register START_CONFIG

7	6	5	4	3	2	1	0
RESERVED						FUNC_MODE
R/W						R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 14. Register START_CONFIG Field Descriptions

Bit

Field

Type

Reset

Description

7:2

RESERVED

R/W

Reserved. Set to b00’0000

1:0

FUNC_MODE

R/W

Functional Mode

Configure functional mode of device. In active mode, the device performs conversions. When in Sleep mode, the LDC1101 is in a reduced power mode; the device should be configured in this mode. Shutdown mode is a minimal current mode in which the device configuration is not retained.

Note that SHUTDOWN_EN must be set to 1 prior to setting FUNC_MODE to b10.

b00: Active conversion mode
b01: Sleep mode (default value)
b10: Set device to shutdown mode
b11: Reserved

8.6.13 Register D_CONFIG (address = 0x0C) [reset = 0x00]

Figure 25. Register D_CONFIG

7	6	5	4	3	2	1	0
RESERVED							DOK_REPORT
R/W							R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 15. Register D_CONFIG Field Descriptions

Bit	Field	Type	Reset	Description
7:1	RESERVED	R/W		Reserved. Set to b000’0000.
0	DOK_REPORT	R/W		Sensor Amplitude Control Continue to convert even if sensor amplitude is not regulated. b0: Require amplitude regulation for conversion (default value) b1: LDC will continue to convert even if sensor amplitude is unable to maintain regulation.

8.6.14 Register L_THRESH_HI_LSB (address = 0x16) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 26. Register L_THRESH_HI_LSB

7	6	5	4	3	2	1	0
L_THRESH_HI[7:0]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 16. Register L_THRESH_HI_LSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

L_THRESH_HI[7:0]

R/W

L High Threshold LSB Setting

Combine with value in Register L_THRESH_HI_MSB (Address 0x17) to set the upper L conversion threshold:

L_ThreshHI = L_THRESH_HI[15:8] ×256 + L_THRESH_HI[7:0]

If L_DATA conversion result is greater than the L_THRESH_HI, L_HIN will be asserted. Note that L_THRESH_HI_LSB is buffered and will not change the device configuration until a write to L_TRESH_HI_MSB.

0x00: default value

8.6.15 Register L_THRESH_HI_MSB (address = 0x17) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 27. Register L_THRESH_HI_MSB

7	6	5	4	3	2	1	0
L_THRESH_HI[15:8]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 17. Register L_THRESH_HI_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	L_THRESH_HI[15:8]	R/W		L High Threshold MSB Setting Combine with value in Register L_THRESH_HI_LSB (Address 0x16) to set the upper L conversion threshold. 0x00: default value

8.6.16 Register L_THRESH_LO_LSB (address = 0x18) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 28. Register L_THRESH_LO_LSB

7	6	5	4	3	2	1	0
L_THRESH_L[7:0]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 18. Register L_THRESH_LO_LSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

L_THRESH_LO[7:0]

R/W

L Low Threshold LSB Setting

Combine with value in Register L_THRESH_LO_MSB (Address 0x19) to set the lower L conversion threshold:

L_ThreshLO = L_THRESH_LO[15:8] ×256 + L_THRESH_LO[7:0]

If L_DATA conversion result is less than the L_THRESH_LO, L_HI_LON will be asserted.

Note that L_THRESH_LO_LSB is buffered and will not change the device configuration until a write to L_TRESH_LO_MSB.

0x00: default value

8.6.17 Register L_THRESH_LO_MSB (address = 0x19) [reset = 0x00]

This register can be modified while the LDC1101 is in active mode.

Figure 29. L_THRESH_LO_MSB

7	6	5	4	3	2	1	0
L_THRESH_L[15:8]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 19. L_THRESH_LO_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	L_THRESH_LO[15:8]	R/W		L Low Threshold MSB Setting Combine with value in Register L_THRESH_LO_LSB (Address 0x18) to set the lower L conversion threshold. 0x00: default value

8.6.18 Register STATUS (address = 0x020 [reset = 0x00]

Figure 30. Register STATUS

7	6	5	4	3	2	1	0
NO_SENSOR_OSC	DRDYB	RP_HIN	RP_HI_LON	L_HIN	L_HI_LON	RESERVED	POR_READ
R	R	R	R	R	R	R	R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 20. Register STATUS Field Descriptions

Bit	Field	Type	Description
7	NO_SENSOR_OSC	R	Sensor Oscillation Not Present Error Indicates that the sensor has stopped oscillating. This error may also be produced if the MIN_FREQ is set to too high a value. b0: Error condition has not occurred b1: LDC1101 has not detected the sensor oscillation.
6	DRDYB	R	RP+L Data Ready b0: New RP+L conversion data is available. b1: No new conversion data is available.
5	RP_HIN	R	RP_DATA High Threshold Comparator Note this field will latch a low value. To clear, write 0x00 to register 0x0A. INTB_FUNC (register 0x0A:bits[5:0]) must be set to b00'0001 for this flag to be reported. b0: RP_DATA measurement has exceeded RP_THRESH_HI b1: RP_DATA measurement has not exceeded RP_THRESH_HI
4	RP_HI_LON	R	RP_DATA Hysteresis Comparator b0: RP_DATA measurement has gone above RP_THRESH_LO. b1: RP_DATA measurement has gone below RP_THRESH_HI.
3	L_HIN	R	L_DATA High Threshold Comparator Note this field will latch a low value. To clear, write 0x00 to register 0x0A. INTB_FUNC (register 0x0A:bits[5:0]) must be set to b00'1000 for this flag to be reported. b0: L_DATA measurement has exceeded L_THRESH_HI b1: L_DATA measurement has not exceeded L_THRESH_HI
2	L_HI_LON	R	L_DATA Hysteresis Comparator b0: L_DATA measurement has gone above L_THRESH_LO. b1: L_DATA measurement has gone below L_THRESH_HI.
1	RESERVED	R	No Function 0: default value
0	POR_READ	R	Device in Power-On-Reset Indicates the device is in process of resetting. Note that the device cannot accept any configuration changes until reset is complete. Wait until POR_READ = 0 before changing any device configuration. b0: Device is not in reset. b1: Device is currently in reset; wait until POR_READ = 0.

8.6.19 Register RP_DATA_LSB (address = 0x21) [reset = 0x00]

Figure 31. Register RP_DATA_LSB

7	6	5	4	3	2	1	0
RP_DATA[7:0]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 21. Register RP_DATA_LSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

RP_DATA[7:0]

RP-Measurement Conversion Result

Combine with values in Register RP_DATA_MSB (Address 0x22) to determine R_P conversion result:

RP_DATA = RP_DATA[15:8]×256 + RP_DATA[7:0]

NOTE: RP_DATA_LSB (Address 0x21) must be read prior to reading the RP_DATA_MSB (Address 0x22) register to properly retrieve conversion results.

8.6.20 Register RP_DATA_MSB (address = 0x22) [reset = 0x00]

Figure 32. Register RP_DATA_MSB

7	6	5	4	3	2	1	0
RP_DATA[15:8]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 22. Register RP_DATA_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RP_DATA[15:8]	R		RP-Measurement Conversion Result Combine with values in Register RP_DATA_LSB (Address 0x21) to determine R_P conversion result: NOTE: RP_DATA_LSB (Address 0x21) must be read prior to reading this register to properly retrieve conversion results.

8.6.21 Register L_DATA_LSB (address = 0x23) [reset = 0x00]

Figure 33. Register L_DATA_LSB

7	6	5	4	3	2	1	0
L_DATA[7:0]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 23. Register L_DATA_LSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

L_DATA[7:0]

L-Measurement Conversion Result

Combine with values in Register L_DATA_MSB (Address 0x24) to determine L conversion result:

L_DATA = L_DATA[15:8]×256 + L_DATA[7:0]

f_SENSOR = ( f_CLKIN ˣ RESP_TIME) / (3 ˣ L_DATA)

NOTE: RP_DATA_LSB (Address 0x21) must be read prior to reading this register to properly retrieve conversion results.

8.6.22 Register L_DATA_MSB (address = 0x24) [reset = 0x00]

Figure 34. Register L_DATA_MSB

7	6	5	4	3	2	1	0
L_DATA[15:8]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 24. Register L_DATA_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	L_DATA[15:8]	R		L-Measurement Conversion Result Combine with values in Register L_DATA_LSB (Address 0x23) to determine L conversion result: NOTE: RP_DATA_LSB (Address 0x21) must be read prior to reading this register to properly retrieve conversion results.

8.6.23 Register LHR_RCOUNT_LSB (address = 0x30) [reset = 0x00]

Figure 35. Register LHR_RCOUNT_LSB

7	6	5	4	3	2	1	0
RCOUNT[7:0]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 25. Register LHR_RCOUNT_LSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	RCOUNT[7:0]	R		High Resolution L-Measurement Reference Count Setting Combine with value in Register LHR_RCOUNT_MSB (Address 0x31) to set the measurement time for High Resolution L Measurements. 0x00: default value

8.6.24 Register LHR_RCOUNT_MSB (address = 0x31) [reset = 0x00]

Figure 36. Register LHR_RCOUNT_MSB

7	6	5	4	3	2	1	0
RCOUNT[15:8]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 26. Register LHR_RCOUNT_MSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

RCOUNT[15:8]

High Resolution L-Measurement Reference Count Setting

Combine with value in Register LHR_RCOUNT_LSB (Address 0x30) to set the measurement time for High Resolution L Measurements.

Higher values for LHR_RCOUNT have a higher effective measurement resolution but a lower sample rate. Refer to LHR Sample Rate Configuration with RCOUNTfor more details.

Measurement Time (t_CONV)= (RCOUNT[15:0] ˣ 16 + 55)/f_CLKIN

RCOUNT = RCOUNT [15:8]×256 + RCOUNT [7:0]
Valid range: 2 ≤ RCOUNT[15:8] ≤ 65535
0x00: default value

8.6.25 Register LHR_OFFSET_LSB (address = 0x32) [reset = 0x00]

Figure 37. Register LHR_OFFSET_LSB

7	6	5	4	3	2	1	0
LHR_OFFSET[7:0]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 27. Register LHR_OFFSET_LSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	LHR_OFFSET[7:0]	R/W		High Resolution L-Measurement Offset Setting Combine with value in Register LHR_OFFSET_LSB (Address 0x32) to set the offset value applied to High Resolution L Measurements. 0x00: default value

8.6.26 Register LHR_OFFSET_MSB (address = 0x33) [reset = 0x00]

Figure 38. Register LHR_OFFSET_MSB

7	6	5	4	3	2	1	0
LHR_OFFSET[15:8]
R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 28. Register LHR_OFFSET_MSB Field Descriptions

Bit	Field	Type	Reset	Description
7:0	LHR_OFFSET[15:8]	R/W		High Resolution L-Measurement Offset Setting Combine with value in Register LHR_OFFSET_LSB (Address 0x32) to set the offset value applied to High Resolution L Measurements. 0x00: default value

8.6.27 Register LHR_CONFIG (address = 0x34) [reset = 0x00]

Figure 39. Register LHR_CONFIG

7	6	5	4	3	2	1	0
RESERVED						SENSOR_DIV
R/W						R/W

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 29. Register LHR_CONFIG Field Descriptions

Bit	Field	Type	Reset	Description
7:2	RESERVED	R/W		Reserved. Set to b00’0000
1:0	SENSOR_DIV	R/W		Sensor Clock Divider Setting Divide the sensor frequency by programmed divider. This divider can be used to set the sensor frequency lower than the reference frequency. Refer to Sensor Input Divider for more details. b00: Sensor Frequency not divided (default value) b01: Sensor Frequency divided by 2 b10: Sensor Frequency divided by 4 b11: Sensor Frequency divided by 8

8.6.28 Register LHR_DATA_LSB (address = 0x38) [reset = 0x00]

Figure 40. Register LHR_DATA_LSB

7	6	5	4	3	2	1	0
LHR_DATA[7:0]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 30. Register LHR_DATA_LSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

LHR_DATA[7:0]

High Resolution L-Measurement Conversion Result

Combine with values in Registers LHR_DATA_MID (Address 0x39) and LHR_DATA_MSB (Address 0x3A) to determine conversion result.

f_SENSOR= f_CLKIN ˣ SENSOR_DIV ˣ LHR_DATA ÷ 2²⁴

NOTE: The LHR_DATA registers must be read in the sequence 0x38 first, then 0x39, and last 0x3A for data coherency.

8.6.29 Register LHR_DATA_MID (address = 0x39) [reset = 0x00]

Figure 41. Register LHR_DATA_MID

7	6	5	4	3	2	1	0
LHR_DATA[15:8]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 31. Register LHR_DATA_MID Field Descriptions

Bit

Field

Type

Reset

Description

7:0

LHR_DATA[15:8]

High Resolution L-Measurement Conversion Result

Combine with values in Registers LHR_DATA_LSB (Address 0x38) and LHR_DATA_MSB (Address 0x3A) to determine conversion result.

NOTE: Register LDR_DATA_LSB must be read prior to this register and LHR_DATA_MSB to ensure data coherency.

8.6.30 Register LHR_DATA_MSB (address = 0x3A) [reset = 0x00]

Figure 42. Register LHR_DATA_MSB

7	6	5	4	3	2	1	0
LHR_DATA[23:16]
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 32. Register LHR_DATA_MSB Field Descriptions

Bit

Field

Type

Reset

Description

7:0

LHR_DATA[23:16]

High Resolution L-Measurement Conversion Result

Combine with values in Registers LHR_DATA_LSB (Address 0x38) and LHR_DATA_MID (Address 0x39) to determine conversion result.

NOTE: Register LDR_DATA_LSB must be read prior to LHR_DATA_MID and this register to ensure data coherency.

8.6.31 Register LHR_STATUS (address = 0x3B) [reset = 0x00]

Figure 43. Register LHR_STATUS

7	6	5	4	3	2	1	0
UNUSED			ERR_ZC	ERR_OR	ERR_UR	ERR_OF	LHR_DRDY
R			R	R	R	R	R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 33. Register LHR_STATUS Field Descriptions

Bit	Field	Type	Description
7:5	UNUSED	R	No Function
4	ERR_ZC	R	Zero Count Error Zero count errors are applicable for LHR measurements and indicate that no cycles of the sensor occurred in the programmed measurement interval. This indicates either a sensor error or the sensor frequency is too low. This field is updated after register 0x38 has been read. b0: No Zero Count error has occurred for the last LHR conversion result read. b1: A Zero Count error has occurred.
3	ERR_OR	R	Conversion Over-range Error Conversion over-range errors are applicable for LHR measurements and indicate that the sensor frequency exceeded the reference frequency. This field is updated after register 0x38 has been read. b0: No Conversion Over-range error has occurred for the last LHR conversion result read. b1: A Conversion Over-range error has occurred.
2	ERR_UR	R	Conversion Under-range Error Conversion under-range errors are applicable for LHR measurements and indicate that the output code is negative; this occurs when programmed LHR offset register value is too large. This field is updated after register 0x38 has been read. b0: No Conversion Under-range error has occurred for the last LHR conversion result read. b1: A Conversion Under-range error has occurred.
1	ERR_OF	R	Conversion Over-flow Error Conversion over-flow errors are applicable for LHR measurements and indicate that the sensor frequency is too close to the reference frequency. This field is updated after register 0x38 has been read. b0: No Conversion Over-flow error has occurred for the last LHR conversion result read. b1: A Conversion Over-flow error has occurred.
0	LHR_DRDY	R	LHR Data Ready b0: Unread LHR conversion data is available. This field is set to 0 at the end of an LHR conversion and remains asserted until a read of register 0x38. b1: No unread LHR conversion data is available.

8.6.32 Register RID (address = 0x3E) [reset = 0x02]

Figure 44. Register RID

7	6	5	4	3	2	1	0
V_ID					RID
R					R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 34. Register RID Field Descriptions

Bit	Field	Type	Reset	Description
7:3	V_ID	R		DEVICE ID Returns fixed value indicating device ID. 0x00: indicates LDC1101 (default value)
2:0	RID	R		RID Returns device RID. b010: Default value

8.6.33 Register DEVICE_ID (address = 0x3F) [reset = 0xD4]

Figure 45. Register DEVICE_ID

7	6	5	4	3	2	1	0
CHIP_ID
R

LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 35. Register DEVICE_ID Field Descriptions

Bit	Field	Type	Reset	Description
7:0	CHIP_ID	R		CHIP_ID Returns fixed value indicating device Family ID. 0xD4: indicates LDC1101 family (default value)

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 Theory of Operation

An AC current flowing through an inductor will generate an AC magnetic field. If a conductive material, such as a metal object, is brought into the vicinity of the inductor, the magnetic field will induce a circulating current (eddy current) on the surface of the conductor. The eddy current is a function of the distance, size, and composition of the conductor.

LDC1101 conductor_ac_magnetic_field_snosd01.gif

Figure 46. Conductor in an AC Magnetic Field

The eddy current generates its own magnetic field, which opposes the original field generated by the inductor. This effect can be considered as a set of coupled inductors, where the inductor is the primary winding and the eddy current in the conductor represents the secondary winding. The coupling between the windings is a function of the inductor, and the resistivity, distance, size, and shape of the conductor.

To minimize the current required to drive the inductor, a parallel capacitor is added to create a resonant circuit, which will oscillate at a frequency given by Equation 1 when energy is injected into the circuit. In this way, the LDC1101 only needs to compensate for the parasitic losses in the sensor, represented by the series resistance R_S of the LC tank. The oscillator is then restricted to operating at the resonant frequency of the LC circuit and injects sufficient energy to compensate for the loss from R_S.

Figure 47. LC Tank

The resistance and inductance of the secondary winding caused by the eddy current can be modeled as a distant dependent resistive and inductive component on the primary side (coil). We can then represent the circuit as an equivalent parallel circuit, as shown in Figure 48.

LDC1101 equivalent_parallel_circuit_snosd01.gif

Figure 48. Equivalent Parallel Circuit

The value of R_P can be calculated with:

Equation 2. LDC1101 Eq02_RP_snosd01.gif

where

R_S is the AC series resistance at the frequency of operation.
C is the parallel capacitance
L is the inductance

R_P can be viewed as the load on the sensor driver; this load corresponds to the current drive needed to maintain the oscillation amplitude. The position of a target can change R_P by a significant amount, as shown in Figure 49. The value of R_P can then be used to determine the position of a conductive target. If the value of R_P is too low, then the sensor driver will not be able to maintain sufficient oscillation amplitude.

LDC1101 D010_change_rp_vs_target_distance_SNOSD01.gif

Figure 49. R_P vs Target Distance for a 14 mm Diameter Sensor

9.1.2 RP+L Mode Calculations

For many systems which use the LDC1101, the actual sensor R_P, sensor frequency, or sensor inductance is not necessary to determine the target position; typically the equation of interest is:

Equation 3. Position_Target = ƒ(RP_DATA) or Position_Target = ƒ(L_DATA)

where

RP_DATA is the contents of registers 0x21 and 0x22
L_DATA is the contents of registers 0x23 and 0x24

These Position equations are typically system dependent. For applications where the Sensor R_P in Ωs needs to be calculated, use Equation 4:

Equation 4. LDC1101 Eq04_Rp_snosd01.gif

where

RPDATA is the contents of RP_DATA_MSB and RP_DATA_LSB (registers 0x21 and 0x22),
RP_MIN is the value set by RP_MIN in register RP_SET (register 0x01), and
RP_MAX is the value set by RP_MIN in register RP_SET (register 0x01).

For example, with device settings of:

RP_MIN set to 1.5 kΩ, and
RP_MAX set to 12 kΩ.

If RPDATA = 0x33F1 (register 0x21 = 0xF1 and register 0x22= 0x33), which is 13297 decimal, then the sensor R_P = 1.824 kΩ.

If RPMAX_DIS (Register 0x01-b[7]) is set, then the equation is simply:

Equation 5. LDC1101 Eq05_rp_snosd01.gif

LDC1101 D012_output_code_vs_sensor_rp_SNOSD01.gif

Figure 50. LDC1101 R_P Transfer Curve with RPMIN = 1.5 kΩ and RPMAX = 24 kΩ

The sensor frequency in Hz can be calculated from Equation 6:

Equation 6. LDC1101 Eq06_fsensor_snosd01.gif

where

ƒ_CLKIN is the frequency input to the CLKIN pin,
L_DATA is the contents of registers 0x23 and 0x24, and
RESP_TIME is the programmed response time in register 0x04.

The inductance in Henrys can then be determined from Equation 7:

Equation 7. LDC1101 Eq07_Lsensor_snosd01.gif

where

C_SENSOR is the fixed sensor capacitance in Farads, and
ƒ_SENSOR is the measured sensor frequency, as calculated in Equation 6 above.

LDC1101 D013_inductance_vs_normalized_target_distance_SNOSD01.gif

Figure 51. Inductance vs Normalized Target Distance for an Example Sensor

9.1.3 LDC1101 R_P Configuration

Setting the RP_MIN and RP_MAX parameters is necessary for proper operation of the LDC1101; the LDC1101 may not be able to effectively drive the sensor with incorrect settings, as the sensor amplitude will be out of the valid operation region. The LDC1101EVM GUI and the LDC Excel® tools spreadsheet (http://www.ti.com/lit/zip/slyc137) can be used to calculate these parameters in an efficient manner.

For R_P measurements, the following register settings must be set as follows:

ALT_CONFIG.LOPTIMAL(register 0x05-bit0) = 0
D_CONFIG.DOK_REPORT (register 0x0C-bit0) = 0

Ensure that the sensor characteristics are within the Sensor boundary conditions:
1. 500 kHz < ƒ_SENSOR < 10 MHz
2. 100 pF < C_SENSOR < 10 nF
3. 1 µH < L_SENSOR < 500 µH
Measure the sensor’s resonance impedance with minimal target interaction (R_PD∞). The minimal target interaction occurs when the target is farthest away from the sensor for axial sensing solutions or when the target coverage of the sensor is at a minimum for rotational or lateral sensing. Select the appropriate setting for RPMAX (register 0x01-bits [5:4]):

R_PD∞ ≤ RPMAX ≤ 2R_PD∞

Measure the sensor’s resonance impedance with the target closest to the sensor (R_PD0) as required by the application. Select the largest RPMIN setting that satisfies:
1. RPMIN < 0.8 × R_PD0
2. If the required RPMIN is smaller than 750 Ω, R_PD0 must be increased to be compliant with this boundary condition. This can be done by one or more of the following:
  1. increasing ƒ_SENSOR
  2. increasing the minimum distance between the target and the sensor
  3. reducing the R_S of the sensor by use of a thicker trace or wire
Check if the worst-case Sensor quality factor Q_MIN=RpMIN × √(C_SENSOR/L_SENSOR) is within LDC1101’s operating range:
1. 10 ≤ Q_MIN ≤ 400
2. If Q_MIN < 10, for a fixed ƒ_SENSOR, increase C_SENSOR and decrease L_SENSOR.
3. If Q_MIN > 400, for a fixed ƒ_SENSOR, decrease C_SENSOR and increse L_SENSOR.
4. Alternatively the user may choose to not change the current Sensor parameters, but to increase Rp_D0.

If the R_P of the sensor is greater than 75 kΩ, R_P measurement accuracy may be improved by setting RPMAX_DIS to 1.

9.1.4 Setting Internal Time Constant 1

R_P Measurements require configuration of the TC1 and TC2 registers. There are several programmable capacitance and resistance values. Set Time Constant 1 based on minimum sensor frequency:

Equation 8. LDC1101 Eq08_R1_snosd01.gif

where

ƒ_SENSOR-MIN is the minimum sensor frequency encountered in the system; typically this occurs with no target present.
V_AMP is sensor amplitude of 0.6V,
R1 is the programmed setting for TC1.R1 (register 0x03-bits[4:0]), and
C1 is the programmed setting for TC1.C1 (register 0x03-bits[7:6])

The acceptable range of R1 is from 20.6 kΩ to 417.4 kΩ. If several combinations of R1 and C1 are possible, it is recommended to use the largest capacitance setting for C1 that fits the constraints of Equation 8, as this will provide improved noise performance.

9.1.5 Setting Internal Time Constant 2

Set the Time Constant 2 (register 0x03) using Equation 9:

Equation 9. R2 × C2 = 2 × RP_MIN × C_SENSOR

where

C_SENSOR is the parallel capacitance of the sensor.
RP_MIN is the LDC1101 setting determined in LDC1101 RP Configuration (for example, use 1.5 kΩ when RP_SET.RP_MIN = b110),
R2 is the programmed setting for TC2.R2 (register 0x03-bits[5:0]), and
C2 is the programmed setting for TC2.C2 (register 0x03-bits[7:6]).

The acceptable range of R2 is from 24.60 kΩ to 834.8 kΩ. If several combinations of R2 and C2 are possible, it is recommended to program the larger capacitance setting for C2 that fits the constraints of Equation 9, as this will provide improved noise performance.

9.1.6 MIN_FREQ and Watchdog Configuration

The LDC1101 includes a watchdog timer which monitors the sensor oscillation. While in active mode, if no sensor oscillation is detected, the LDC1101 will set STATUS.NO_SENSOR_OSC (register 0x20:bit7), and attempt to restart the oscillator. This restart will reset any active conversion.

The watchdog waits an interval of time based on the setting of DIG_CONF.MIN_FREQ (register 0x04:bits[7:4]). The MIN_FREQ setting is also used to configure the startup of oscillation on the sensor. Select the DIG_CONF.MIN_FREQ (register 0x04-bits[7:4]) setting closest to the minimum sensor frequency; this setting is used for internal watchdog timing. If the watchdog determines the sensor has stopped oscillating, it will report the sensor has stopped oscillating in STATUS. NO_SENSOR_OSC (register 0x20-bit7). If the DIG_CONF.MIN_FREQ is set too low, then the LDC1101 will take a longer time interval to report that the sensor oscillation has stopped.

If the DIG_CONF.MIN_FREQ is set too high, then the watchdog may incorrectly report that the sensor has stopped oscillating and attempt to restart the sensor oscillation.

When the watchdog determines that the sensor has stopped oscillating, the LHR conversion results will contain 0xFFFFFF.

9.1.7 RP+L Sample Rate Configuration with RESP_TIME

The RP+L sample rate can be adjusted by setting by DIG_CONF.RESP_TIME (register 0x04:bits[2:0]). The Response time can be configured from 192 to 6144 cycles of the sensor frequency. Higher values of Response time will have a slower sample rate, but produce a higher resolution conversion.

Equation 10. LDC1101 Eq10_conv_snosd01.gif

9.1.8 High Resolution Inductance Calculation (LHR mode)

For many systems which use the LDC1101, the actual sensor frequency or sensor inductance is not necessary to determine the target position. Should the sensor frequency in Hz need to be determined, use Equation 11:

Equation 11. LDC1101 Eq11_fsensor_snosd01.gif

where

LHRDATA is the contents of registers 0x38, 0x39, and 0x3A,
LHROFFSET is the programmed contents of registers 0x32 and 0x33,
SENSOR_DIV is the contents of LHR_CONFIG.SENSOR_DIV (register 0x34-bit[1:0]), and
ƒ_CLKIN is the frequency input to the CLKIN pin: ensure that it is within the specified limits of 1 MHz to 16 MHz.

Note that LHR_DATA=0x0000000 indicates a fault condition or that the LDC1101 has never completed an LHR conversion.

The inductance in Henrys can then be determined from the sensor frequency with Equation 12:

Equation 12. LDC1101 Eq12_Lsen_snosd01.gif

where

C_SENSOR is the fixed sensor capacitance, and
ƒ_SENSOR is the measured sensor frequency, as calculated above.

Example with the device set to:

LHR_OFFSET = 0x00FF (register 0x32 = 0xFF, and 0x33 = 0x00)
ƒ_CLKIN = 16 MHz
SENSOR_DIV = b’01 (divide by 2)

and the conversion result is:

LHR_DATA = 0x123456 (register 0x38 = 0x56, register 0x39 = 0x34,register 0x3A = 0x12)

Then entering LHR_DATA = 0x123456 = 1193046 (decimal) into Equation 11:

Equation 13. LDC1101 Eq13_fsensor_snosd01.gif

Results in ƒ_SENSOR = 2.400066 MHz.

9.1.9 LHR Sample Rate Configuration with RCOUNT

The conversion time represents the number of reference clock cycles used to measure the sensor frequency. The LHR mode conversion time is set by the Reference count in LHR_RCOUNT.RCOUNT (registers 0x30 & 0x31). The LHR conversion time is:

Equation 14. LDC1101 Eq14_tconv_snosd01.gif

The 55 is due to post-conversion processing and is a fixed value. The reference count value must be chosen to support the required number of effective bits (ENOB). For example, if an ENOB of 13 bits is required, then a minimum conversion time of 2¹³ = 8192 clock cycles is required. 8192 clock cycles correspond to a RCOUNT value of 0x0200.

Higher values for RCOUNT produce higher resolution conversions; the maximum setting, 0xFFFF, is required for full resolution.

9.1.10 Setting RPMIN for LHR Measurements

Configure the R_P measurement as shown previously for L measurements. If only L measurements are necessary, then the R_P measurement can be disabled by setting:

ALT_CONFIG.LOPTIMAL(register 0x05-bit0) = 1
D_CONFIG.DOK_REPORT (register 0x0C-bit0) = 1

Setting these bits disable the sensor modulation used by the LDC1101 to measure R_P and can reduce L measurement noise. When the R_P modulation is disabled, the LDC1101 will drive a fixed current level into the sensor. The current drive is configured by RP_SET.RPMIN (address 0x01:bits[2:0]). The sensor amplitude must remain between 0.25 Vpk and 1.25 Vpk for accurate L measurements. Use Table 36 to determine the appropriate RPMIN setting, based on the variation in sensor R_P. If multiple RPMIN values cover the Sensor R_P, use the higher current drive setting. The equation to determine sensor amplitude is:

Equation 15. LDC1101 Eq15_Rp_snosd01.gif

Table 36. LHR RPMIN Settings when Sensor R_P Modulation is Disabled

RPMIN SETTING	RPMIN FIELD VALUE	SENSOR DRIVE (μA)	MINIMUM SENSOR R_P (kΩ)	MAXIMUM SENSOR R_P (kΩ)
0.75 kΩ	b111	600	0.53	1.65
1.5 kΩ	b110	300	1.1	3.3
3 kΩ	b101	150	2.1	6.5
6 kΩ	b100	75	4.2	13.1
12 kΩ	b011	37.5	8.4	26.2
24 kΩ	b010	18.7	16.9	52.4
48 kΩ	b001	9.4	33.9	105
96 kΩ	b000	4.7	67.9	209

For example, with a sensor that has an R_P which can vary between 2.7 kΩ to 5 kΩ, the appropriate setting for RPMIN would be 3 kΩ (RP_SET.RPMIN = b101). For more information on Sensor R_P and sensor drive, refer to Configuring Inductive-to-Digital-Converters for Parallel Resistance (RP) Variation in L-C Tank Sensors(SNAA221).

9.1.11 Sensor Input Divider

The reference clock frequency should be greater than 4 times the sensor frequency for optimum measurement resolution:

ƒ_CLKIN> 4ƒ_SENSOR-MAX

For higher sensor frequencies, this relationship may not be realizable without the sensor divider. Set the sensor divider to an appropriate value to produce an effective reduction in the sensor frequency:

ƒ_CLKIN> 4ƒ_SENSOR-MAX ÷ SENSOR_DIV

9.1.12 Reference Clock Input

Use a clean, low jitter, 40-60% duty cycle clock input with an amplitude swing within the range of V_DD and GND; proper clock impedance control, and series or parallel termination is recommended. The rise and fall time should be less than 5 ns. Do not use a spread-spectrum or modulated clock.

For optimum L measurement performance, it is recommended to use the highest reference frequency (16 MHz). LHR conversions will not start until a clock is provided on CLKIN.

9.1.13 INTB Reporting on SDO

INTB is a signal generated by the LDC1101 that reports a change in device status. When INTB_MODE.INTB2SDO=1 (register 0x0A:bit7), INTB is multiplexed onto the SDO pin. Once the reporting is enabled, select the desired signal to report by setting INTB_MODE.INTB_FUNC (register 0x0A:bit[5:0]).

LDC1101 sdo_intb_connection_to_mcu_snosd01.gif

Figure 52. SDO/INTB Connection to MCU

For many microcontrollers, the MISO signal on the SPI peripheral cannot provide the desired interrupt functionality. One method to use the INTB functionality is to connect a second GPIO which triggers on a falling edge, as shown in Figure 51. Table 37 describes the signal functionality that can be programmed onto INTB.

Table 37. INTB Signal Options

SIGNAL	INTB_FUNC (0x0A:bit[5:0])	FUNCTIONALITY	SWITCH OUTPUT TYPE
LHR Data Ready (LHR-DRDY)	b10’0000	Indicates new High-Resolution Inductance (LHR) conversion data is available.	Latching
L_HI_LO	b01’0000	L Comparator with hysteresis	Hysteresis
L_TH_HI	b00’1000	Latching L High threshold compare	Latching
RP+L Data Ready (RPL-DRDY)	b00’0100	Indicates new RP+L conversion data is available.	Pulse
RP_HI_LO	b00’0010	R_P Comparator with hysteresis	Hysteresis
RP_TH_HI	b00’0001	Latching R_P High threshold compare	Latching
None	b00’0000	No INTB reporting – SDO pin only provides SDO functionality.	N/A

LDC1101 example_intb_signal_on_sdo_snosd01.gif

Figure 53. Example INTB Signal on SDO

When INTB_MODE.INTB2SDO (register 0x0A:bit7) = 0, the SDO pin is in a Hi-Z state until the 8^th falling edge of SCLK after CSB goes low. When INTB reporting is enabled by setting INTB_MODE.INTB2SDO = 1, after CSB goes low, the SDO pin will go high and remain high until:

the event configured by INTB_MODE.INTB_FUNC occurs,
an SPI read transaction is initiated, or
CSB is deasserted (pulled high)

9.1.14 DRDY (Data Ready) Reporting on SDO

Completion of a conversion can be indicated on the SDO pin by reporting the DRDY signal – there is a conversion complete indicator for the RP+L conversion (RPL-DRDY), and a corresponding conversion complete indicator for the LHR mode (LHR-DRDY).

When LHR-DRDY or RPL-DRDY is reported on SDO, the SDO pin is asserted on completion of a conversion. While in this mode, conversion data can be corrupted if a new conversion completes while reading the output data registers. To avoid data corruption, it is important to retrieve the conversion rates via SPI quicker than the shortest conversion interval, and to ensure that the data is retrieved before a new conversion could possibly complete.

When INTB is reporting RPL-DRDY, if CSB is held low for longer than one conversion cycle, INTB will be deasserted approximately 100 ns to 2 µs prior to the completion of each conversion. The deassertion time is proportional to 1/ƒ_SENSOR.

When INTB is reporting LHR-DRDY, if CSB is held low for longer than one conversion cycle, INTB will assert on completion of the first conversion and remain low – and it will remain asserted until cleared. To clear the LHR_DRDY signal, read the LHR_DATA registers.

LDC1101 reporting_rpl_drdy_on_intb_sdo_snosd01.gif

Figure 54. Reporting RPL-DRDY on INTB/SDO

LDC1101 reporting_lhr_drdy_on_intb_sdo_snosd01.gif

Figure 55. Reporting LHR-DRDY on INTB/SDO

Note that the conversion interval for an LHR measurement is asynchronous to the conversion interval for an R_P+L measurement, therefore the LHR-DRDY signal cannot be used to determine when to read R_P+L conversion results, and vice versa.

9.1.15 Comparator Functionality

The LDC1101 provides comparator functionality, in which the RP+L conversion results can be compared against two thresholds. The results of each R_P and L conversion can be compared against programmable thresholds and reported in the STATUS register. Note that the LHR conversion results cannot be used for comparator functionality.

In addition, the INTB signal can be asserted or deasserted when the conversion results increase above a Threshold High or decreases below a Threshold Low registers. In this mode, the LDC1101 essentially behaves as a proximity switch with programmable hysteresis. The threshold HI settings must be programmed to a higher value than the threshold LO registers (for example, if RP_THRESH_LO is set to 0x2000, RP_THRESH_HI should programmed to 0x2001 or higher).

Either Latching and non-latching functions can be reported on INTB/SDO. The INTB signal can report a latching signal or a continuous comparison for each conversion result.

The Threshold setting registers (address 0x06:0x09 and 0x16:0x19) can be changed while the LDC1101 is in active conversion mode. It is recommended to change the register values using an extended SPI transaction as described in SPI Programming, so that the register updates can be completed in a shorter time interval. This functionality enables the LDC1101 to operate as a dynamic tracking switch. LDC1101 output codes can be readout in < 4 μs, and the set of active thresholds can be updated in <6 μs. It is not recommended to update the threshold registers more often than once per conversion interval of the LDC1101 (that is, do not change the threshold register values multiple times in a single conversion interval).

To clear a latched INTB signal, set INTB_MODE = 0x80; it is not necessary for the LDC1101 to be in Sleep mode to clear the latched output; the INTB_MODE can be changed while the LDC1101 is in active mode. After clearing the latched output, re-enabling the INTB_FUNC can be done while in active mode.

Table 38. Comparator Options

FUNCTION	THRESHOLD HIGH	THRESHOLD LOW	STATUS REPORTING	INTB/SDO REPORTING
R_P Comparator with hysteresis	RP_THRESH_HI (registers 0x06 & 0x07)	RP_THRESH_LO (registers 0x08 & 0x09)	RP_HI_LON (bit 4)	RP_HI_LO (INTB_MODE:INTB_FUNC=b00’0010)
R_P High threshold only (Latching)	RP_THRESH_HI (registers 0x06 & 0x07)	N/A	RP_HIN (bit 5)	RP_TH_HI (INTB_MODE:INTB_FUNC=b00’0001) Note that INTB/SDO will latch.
L Comparator with hysteresis	L_THRESH_HI (registers 0x16 & 0x17)	L_THRESH_LO (registers 0x18 & 0x19)	L_HI_LON (bit 2)	L_HI_LO (INTB_MODE:INTB_FUNC=b01’0000)
L High threshold compare only (Latching)	L_THRESH_HI (registers 0x18 & 0x19)	N/A	L_HIN (bit 3)	L_TH_HI (INTB_MODE:INTB_FUNC=b00’1000) Note that INTB/SDO will latch.

space

LDC1101 intb_sdo_output_value_rp_comparator_snosd01.gif

Figure 56. INTB/SDO Output Value for R_P Comparator with Hysteresis (INTB_FUNC=b00’0010)

LDC1101 intb_sdo_output_for_rp_threshold_high_snosd01.gif

Figure 57. INTB/SDO Output for R_P Threshold High (INTB_FUNC=b00’00011)

9.2 Typical Application

Implementation of a system using the LDC1101 first requires determining the appropriate measurement to perform. Refer to http://e2e.ti.com/blogs_/b/analogwire/archive/2015/02/11/inductive-sensing-should-i-measure-l-rp-or-both for guidance.

For systems that require measurement of R_P, set the following:

Configure R_P settings as instructed in LDC1101 RP Configuration.
Set the internal time constants as detailed in Setting Internal Time Constant 1 and Setting Internal Time Constant 2.

LDC1101 detailed_design_procedure_schematic_snosd01.gif

Figure 58. Example LDC1101 Typical Application

9.2.1 Design Requirements

Example of an axial measurement implementation using the LDC1101. In this example, the sensor is an inductor constructed of a multi-layer PCB coil in parallel with a C0G grade surface mount capacitor. For this example, a 10 mm diameter Aluminum target of 1mm thickness is moved perpendicular to the plane of the sensor coil.

For this example, the target range of motion is from 1 mm to 3 mm distance from the sensor coil. The position of the target needs to be reported at a sample rate of 3 ksps. The PCB is a 4-layer construction with 0.1 mm (4 mils) minimum feature size.

9.2.2 Detailed Design Procedure

9.2.2.1 Device Configuration for R_P+L Measurement with an Example Sensor

The sensor described in Table 39 meets the restrictions on size on construction. To use it for R_P+L measurement of a 10 mm diameter 1 mm thick Aluminum target moving axially with respect to the sensor:

Table 39. Example Sensor Characteristics

PARAMETER	MINIMUM TARGET INTERACTION	STRONGEST TARGET INTERACTION
Inductance	5.47 µH	5.15 µH
Inductor Outer Diameter	10 mm
Number of Turns	17
Trace Spacing/ Trace Width	0.1 mm / 0.16 mm
Number of Layers/Separation	2 / 0.355 mm
Sensor Capacitance	270 pF
Sensor Frequency	4.11 MHz	4.27 MHz
R_S	3.20 Ω at 2.93 MHz	3.23 Ω at 4.27 MHz
R_P	6.33 kΩ at 2.93 MHz	5.91 kΩ at 4.27 MHz
Q at 2.9 MHz	45	42

This sensor is within the LDC1101 sensor boundary conditions for frequency, Q, and R_P. The first step is to determine the appropriate RPMIN/RPMAX and TC1/2 settings.

Setting RPMAX has the constraint of R_PD∞ ≤ RpMAX ≤ 2R_PD∞

6.11 kΩ ≤ RPMAX ≤ 12.22 kΩ → Set RPMAX to 12 kΩ

RPMIN setting using the constraint of RpMIN < 0.8 × R_PD0:

0.8 × 3.20 kΩ = 2.6 kΩ → Set RPMIN to 1.5 kΩ. Therefore, set RPMIN = 1.5 kΩ.

Q Range: In step 4, the sensor Q range of 42 to 45 is within the operating range of 10 to 400. As the sensor Q value is below 50, it is not necessary to use RPMAX_DIS, and so RPMAX_DIS=0.
Now set the Time Constant 1 using Equation 8:

R1 × C1 = 0.75026 ÷ 4.11 MHz = 1.8255E-7s
Starting with the largest C1 value of 6 pF for best noise performance results in R1 = 30.5 kΩ.
This is within the R1 range of 20.6 kΩ to 417.4 kΩ, and so C1 = 6 pF can be used.
Picking the next higher programmable value for R1 → Set R1 = 33.9 kΩ.

Next, set the Time Constant 2 using Equation 9:

R2 × C2 = 2 × 1.5 kΩ × 270 pF = 8.100E-7s
Starting with the largest C2 value of 24 pF (once again, for best noise performance) results in
R2 = 33.75 kΩ.
This is within the programmable R2 value of 24.60 kΩ to 834.8 kΩ, and so 24 pF can be used for C2.
Picking the next higher programmable value for R2 → Set R2 = 43.3 kΩ.

Then configure the MIN_FREQ field. The sensor minimum frequency is 4.11 MHz, which occurs with the minimum target interaction. Therefore, MIN_FREQ is set to 14, which configures the watchdog for 4.0 MHz.
Next, set the response time. Setting 6144 will provide the highest resolution R_P measurement with this sensor. With 6144 the sample rate will be at least 2.01 kSPS. To attain highest resolution with a sample rate of >3 kSPS, the response time setting should be 3072.
All other device settings can be in their default values.

Table 40. LDC1101 Register Settings for RP+L Example Application

FIELD	FIELD SETTING	FIELD VALUE	REGISTER	REGISTER VALUE
RPMAX_DIS	disabled	b0	RP_SET (0x01)	0x36
RPMAX	12.0 kΩ	b011
RPMIN	1.5 kΩ	b110
C1	6 pF	b11	TC1 (0x02)	0xDE
R1	33.9 kΩ	b1’1110	TC1 (0x02)	0xDE
C2	24 pF	b11	TC2 (0x03)	0xFE
R2	43.3 kΩ	b11’1110	TC2 (0x03)	0xFE
MIN_FREQ	4.0 MHz	b1110	DIG_CONF (0x04)	0xE6
RESP_TIME	3072	b110	DIG_CONF (0x04)	0xE6
FUNC_MODE	active	b00	START_CONFIG (0x0B)	0x00

On power-up, the LDC1101 enters Sleep mode, which is a low power mode used to configure the LDC. If the LDC1101 is actively converting, write 0x01 to START_CONFIG (address 0x0B) to stop conversions before writing the settings above.

Once the LDC1101 is configured, the process to retrieve RP+L conversion results is:

Set the LDC1101 into conversion mode (active mode) by writing 0x00 to START_CONFIG (register 0x0B).
Poll STATUS.DRDYB (register 0x20:bit6) until it indicates a conversion result is present, or use the INTB signal reporting as described in DRDY (Data Ready) Reporting on SDO.
If the desired measurement is R_P, then read back registers 0x21 and 0x22. The R_P output code is the contents of register 0x21 + 256 × (contents of register 0x22).
If the desired measurement is L, then read back registers 0x23 and 0x24. The L output code is the contents of register 0x23 + 256 × (contents of register 0x24). Reading both R_P and L is permitted, for a more efficient operation R_P and L registers can be retrieved in a single extended SPI transaction as described in SPI Programming.
Process the conversion results on the MCU and repeat from step 2 if additional conversions are desired. If no additional conversions are required, place the LDC1101 into Sleep mode or Shutdown mode.

9.2.2.2 Device Configuration for LHR Measurement with an Example Sensor

Given a sensor with characteristics as shown in Table 39, the steps to configure the LDC1101 for LHR measurements are:

Determine the device sample rate, based on system requirements, using Equation 14. For this example, ƒ_CLKIN = 16 MHz and a sample rate of 3 kSPS is necessary. The number of cycles of the ƒ_CLKIN that closest fit the desired sample rate is determined by:
mm 1/(3 kSPS) = 333.3 µs
subtracting the conversion post-processing time of 55 reference clock cycles (55/16 MHz = 3.437 µs):
mm 333.3 µs – 3.437 µs = 329.9 µs → 16 MHz × 163.2 µs = 5278.34 → 5278.34/16 = 329.9
Programming RCOUNT to 330 (0x014A) results in a sample rate of 2.999 kSPS.
Next, set the sensor drive. If the sensor was already configured for RP+L measurements with the steps in Device Configuration for RP+L Measurement with an Example Sensor, then the sensor drive is already configured and no additional steps are necessary.
If the sensor drive needs to be configured, from Table 36, 3 kΩ is the appropriate setting for the sensor R_P range of 6.33 kΩ to 5.61 kΩ.

Table 41. LDC1101 Register Settings for LHR Example Application

FIELD	FIELD SETTING	FIELD VALUE	REGISTER	REGISTER VALUE
RPMAX_DIS	disabled	b0	RP_SET (0x01)	0x75
RPMAX	doesn’t matter	b111
RPMIN	1.5 kΩ	b101
MIN_FREQ	4.0 MHz	b1110	DIG_CONF (0x04)	0xE7
RESP_TIME	don’t care	b111	DIG_CONF (0x04)	0xE7
RCOUNT	5280	330	LHR_RCOUNT_LSB (0x30)	0x4A
RCOUNT	5280	330	LHR_RCOUNT_MSB (0x31)	0x01
FUNC_MODE	active	b00	START_CONFIG (0x0B)	0x00

Once the LDC1101 is configured, the process to retrieve LHR conversion results is:

Set the LDC1101 into conversion mode (active mode) by writing 0x00 to START_CONFIG (register 0x0B).
Poll LHR_STATUS.DRDYB (register 0x3B:bit0) until it indicates a conversion result is present, or use the INTB signal reporting as described in DRDY (Data Ready) Reporting on SDO.
Read back registers 0x38, 0x39, and 0x3A. These registers can be retrieved in a single extended SPI transaction as described in SPI Programming.
Process the conversion results on the MCU and repeat from step 2 if additional conversions are desired. If no additional conversions are required, place the LDC1101 into Sleep mode or Shutdown mode.

Both sets of conversion results can be retrieved when the conversions complete. Note that the RP+L conversions will not complete at the same time as LHR conversions.

9.2.3 Application Curves

The RCOUNT = 0x00FF curve, which corresponds to a sample rate of 3.87 ksps, will measure the target position with a slightly lower resolution than the RCOUNT = 0x014A used in this example. Over the target movement range of 3 mm, which corresponds to the normalized value of 0.3 on the Axial Measurement graph, the target position can be resolved to 4 µm.

LDC1101 D014_lhr_axial_measure_resolution_vs_normalized_distance_SNOSD01.gif

Figure 59. LHR Axial Measurement Resolution vs Normalized Distance for Aluminum Target

LDC1101 D015_lhr_output_code_vs_normalized_distance_SNOSD01.gif

Figure 60. LHR Output Code vs Normalized Distance for Aluminum Target