LMT70、LMT70A ±0.05°C 精密模拟温度传感器、RTD 和精密 NTC 热敏电阻 IC
- ZHCSDV8A March 2015 – July 2015 LMT70 , LMT70A
  
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LMT70、LMT70A ±0.05°C 精密模拟温度传感器、RTD 和精密 NTC 热敏电阻 IC

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

精度：
- 20°C 至 42°C 范围内为 ±0.05°C（典型值）或 ±0.13°C（最大值）
- -20°C 至 90°C 范围内为 ±0.2°C（最大值）
- 90°C 至 110°C 范围内为 ±0.23°C（最大值）
- -55°C 至 150°C 范围内为 ±0.36°C（最大值）
宽温度范围：−55°C 至 150°C
卷带包装中相邻两个 LMT70A 的温度匹配：30°C 时为 0.1°C（最大值）
带有输出使能引脚的超线性模拟温度传感器
负温度系数 (NTC) 输出斜率：-5.19mV/°C
R_{DS on} < 80Ω 时输出开启/关闭开关
宽电源范围：2.0V 至 5.5V
低电源电流：9.2µA（典型值）12µA（最大值）
超小型 0.88mm x 0.88mm 4 凸点 WLCSP (DSBGA) 封装

2 应用

物联网 (IoT) 传感器节点
工业电阻式温度检测器 (RTD)（AA 类）或精密 NTC/正温度系数 (PTC) 热敏电阻的替代产品
医疗/健身设备
医疗温度计
人体温度监视器
计量温度补偿

3 说明

LMT70 是一款带有输出使能引脚的超小型、高精度、低功耗互补金属氧化物半导体 (CMOS) 模拟温度传感器。 LMT70 几乎适用于所有高精度、低功耗的经济高效型温度感测应用，例如物联网 (IoT) 传感器节点、医疗温度计、高精度仪器仪表和电池供电设备。 LMT70 也是 RTD 和高精度 NTC/PTC 热敏电阻的理想替代产品。

多个 LMT70 可利用输出使能引脚来共用一个模数转换器 (ADC) 通道，从而简化 ADC 校准过程并降低精密温度感测系统的总成本。 LMT70 还具有一个线性低阻抗输出，支持与现成的微控制器 (MCU)/ADC 无缝连接。 LMT70 的热耗散低于 36µW，这种超低自发热特性支持其在宽温度范围内保持高精度。

LMT70A 具有出色的温度匹配性能，同一卷带中取出的相邻两个 LMT70A 的温度最多相差 0.1°C。因此，对于需要计算热量传递的能量计量应用而言，LMT70A 是一套理想的解决方案。

器件信息⁽¹⁾

器件型号	封装	封装尺寸（标称值）
LMT70	DSBGA - WLCSP (4) YFQ	0.88mm x 0.88mm

(1) 要了解所有可用封装，请见数据表末尾的可订购产品附录。

4 宽温度范围、精密、有源 RTD 或 NTC 的替代产品（−55°C 至 150°C）

4.0.0.1 LMT70 精度与温度间的关系

5 修订历史记录

Changes from * Revision (March 2015) to A Revision

Added 典型精度规范。Go
已将 ±0.2°C 精度的温度范围从“20°C 至 90°C”扩展至“-20°C 至 90°C”。Go
Added 9.2µA（典型值）Go
Updated schematicGo
Added -20°C accuracy specification Go
Changed from 20°C to 20°C to 42°C for accuracy specification condition Go
Added 50°C accuracy specification Go
Added typical supply current specification.Go
Changed from 942.547 to 942.552Go
Changed from 943.907 to 943.902Go
Changed from 890.423 to 890.500Go
Changed from 891.934 to 891.857Go
Added -20°C histogram curveGo
Removed erroneous 10°C histogramGo
Changed y axis units from (V) to (mV)Go
Added Output Noise vs Frequency curveGo

6 Device Comparison Table

Order Number	Matching Specification Provided⁽¹⁾
LMT70YFQR, LMT70YFQT	No
LMT70AYFQR, LMT70AYFQT	Yes, 0.1°C at approximately 30°C⁽¹⁾

(1) In order to meet the matching specification of the LMT70A, two units must be picked from adjacent positions from one tape and reel. If PCB rework is required, involving the LMT70A, then the pair of the LMT70A matched units must be replaced. Matching features (which include, without limitation, electrical matching characteristics of adjacent Components as they are delivered in original packaging from TI) are warranted solely to the extent that the purchaser can demonstrate to TI’s satisfaction that the particular Component(s) at issue were adjacent in original packaging as delivered by TI. Customers should be advised that the small size of these Components means they are not individually traceable at the unit level and it may be difficult to establish the original position of the Components once they have been removed from that original packaging as delivered by TI.

7 Pin Configuration and Functions

DSBGA or WLCSP

4 Pins YFQ

(Top View)

Pin Functions

PIN		TYPE	EQUIVALENT CIRCUIT	DESCRIPTION
NAME	NO.	TYPE	EQUIVALENT CIRCUIT	DESCRIPTION
GND	A1	Ground		Ground reference for the device
VDD	A2	Power		Supply voltage
TAO	B1	Analog Output		Temperature analog output pin
T_ON	B2	Digital Input		T_ON pin. Active High input. If T_ON = 0, then the TAO output is open. If T_ON = 1, then TAO pin is connected to the temperature output voltage. Tie this pin to VDD if not used.

8 Specifications

8.1 Absolute Maximum Ratings⁽¹⁾⁽²⁾

	MIN	MAX	UNIT
Supply voltage	−0.3	6	V
Voltage at T_ON and TAO	−0.3	6	V
Current at any pin		5	mA
Storage temperature, T_stg	-65	150	°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) Soldering process must comply with Reflow Temperature Profile specifications. Refer to www.ti.com/packaging.

8.2 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⁾	±750	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.

8.3 Recommended Operating Conditions

	MIN	NOM	MAX	UNIT
Specified temperature (T_MIN ≤ T_A ≤ T_MAX)	−55		150	°C
Supply voltage	2.0		5.5	V

8.4 Thermal Information

THERMAL METRIC⁽¹⁾		LMT70	UNIT
		DSBGA or WLCSP
		YFQ 4 PINS
R_θJA	Junction-to-ambient thermal resistance	187	°C/W
R_θJC(top)	Junction-to-case (top) thermal resistance	2.3
R_θJB	Junction-to-board thermal resistance	105
ψ_JT	Junction-to-top characterization parameter	10.9
ψ_JB	Junction-to-board characterization parameter	104
	Thermal response time to 63% of final value in stirred oil (dominated by PCB see layout)	1.5	sec
	Thermal response time to 63% of final value in still air (dominated by PCB see layout)	73	sec

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

8.5 Electrical Characteristics

Limits apply for T_A = T_J = T_MIN to T_MAX and VDD of 2.00V to 5.5V and VDD ≥ V_TAO + 1V, unless otherwise noted.

PARAMETER		TEST CONDITIONS		MIN	TYP	MAX	UNIT
TEMPERATURE ACCURACY
	TAO accuracy (These stated accuracy limits are with reference to the values in Electrical Characteristics Temperature Lookup Table (LUT), LMT70 temperature-to-voltage.)⁽¹⁾	T_A = –55°C	VDD = 2.7 V	-0.33		0.33	°C
		T_A = –40°C	VDD = 2.7 V	–0.27		0.27
		T_A = –20°C	VDD = 2.7 V	–0.2		0.2
		T_A = –10°C	VDD = 2.7 V	–0.18		0.18
		T_A = 20°C to 42°C	VDD = 2.7 V	–0.13	±0.05	0.13
		T_A = 50°C	VDD = 2.7 V	-0.15		0.15
		T_A= 90°C	VDD = 2.7 V	–0.20		0.20
		T_A = 110°C	VDD = 2.7 V	–0.23		0.23
		T_A = 150°C	VDD = 2.7 V	–0.36		0.36
ATC	Accuracy temperature coefficient (note, uses end point calculations)⁽²⁾	VDD = 2.7V		-2.6		+2.6	m°C/°C
APSS	Accuracy power supply sensitivity (note uses end point calculations)	–55°C ≤ T_A ≤ 10°C	VDD = V_TAO + 1.1 V to 4.0 V	–9	–2	8	m°C /V
		10°C ≤ T_A ≤ 120°C	VDD = 2.0 V to 4.0 V	–9	–2	8
		120°C ≤ T_A ≤ 150°C	VDD = 2.0 V to 4.0 V	–15		8
			VDD = 4 V to 5.5 V	–30	–12	0
V_TAO	Output Voltage	T_A = 30°C	VDD = 2.7 V		943.227		mV
	Sensor gain				–5.194		mV/°C
	Matching of two adjacent parts in tape and reel for LMT70AYFQR, LMT70AYFQT only (see curve Figure 19 for specification at other temperatures)⁽³⁾⁽²⁾	T_A approximately 30°C	V_DD = 2.0 V to 3.6 V			0.1	°C
		T_A = 30°C to 150°C	V_DD = 2.0 V to 3.6 V			2.5	m°C /°C
		T_A = 20°C to 30°C	V_DD = 2.0 V to 3.6 V	-2.5
		T_A = -55°C to 30°C	V_DD = 2.7 V to 3.6 V	–2.5
	Time stability⁽⁴⁾	10k hours at 90°C		–0.1	±0.01	0.1	°C
ANALOG OUTPUT
	Operating output voltage change with load current	0 µA≤I_L≤5 µA		0		0.4	mV
	Operating output voltage change with load current	-5 µA≤I_L≤0 µA		-0.4		0	mV
ROUT	Output Resistance				28	80	Ω
	TAO Off Leakage Current	V_TAO ≤ VDD – 0.6v, V_{T_ON}=GND			0.005	0.5	µA
	TAO Off Leakage Current	V_TAO ≥ 0.2V, V_{T_ON} = GND		-0.5	-0.005		µA
	Output Load Capacitance					1100	pF
POWER SUPPLY
VDO	Dropout Voltage (VDD-V_TAO)⁽⁵⁾	–20°C ≤ T_A ≤ 20°C		1.0			V
VDO	Dropout Voltage (VDD-V_TAO)⁽⁵⁾	–55°C ≤ T_A ≤ –20°C		1.1			V
	Power Supply Current				9.2	12	µA
	Shutdown Current	VDD ≤ 0.4V (-55°C to +110°C)				50	nA
	Shutdown Current	VDD ≤ 0.4V (+110°C to +150°C)				350	nA
LOGIC INPUT
	T_ON Logic Low Input Threshold	-55°C to +150°C		0.5	0.33*VDD		V
	T_ON Logic High Input Threshold	-55°C to +150°C			0.66*VDD	VDD-0.5	V
	T_ON Input Current	V_{T_ON} = VDD			0.15	1	µA
	T_ON Input Current	V_{T_ON} = GND		-1	-0.02		µA

(1) Accuracy is defined as the error between the measured and reference output voltages, tabulated in the Conversion Table at the specified conditions of supply voltage and temperature (expressed in °C). These stated accuracy limits are with reference to the values in Electrical Characteristics Temperature Lookup Table (LUT), see Accuracy Curve for other temperatures. Accuracy limits do not include load regulation or aging; they assume no DC load.

(2) The accuracy temperature coefficient specification is given to indicate part to part performance and does not correlate to the limits given in the curve Figure 3.

(3) In order to meet the matching specification of the LMT70A, two units must be picked from adjacent positions from one tape and reel. If PCB rework is required, involving the LMT70A, then the pair of the LMT70A matched units must be replaced. Matching features (which include, without limitation, electrical matching characteristics of adjacent Components as they are delivered in original packaging from TI) are warranted solely to the extent that the purchaser can demonstrate to TI’s satisfaction that the particular Component(s) at issue were adjacent in original packaging as delivered by TI. Customers should be advised that the small size of these Components means they are not individually traceable at the unit level and it may be difficult to establish the original position of the Components once they have been removed from that original packaging as delivered by TI.

(4) Determined using accelerated operational life testing at 150°C junction temperature; not tested during production.

(5) Dropout voltage (VDO) is defined as the smallest possible differential voltage measured between V_TAO and VDD that causes the temperature error to degrade by 0.02°C.

8.6 Electrical Characteristics Temperature Lookup Table (LUT)

applies for VDD of 2.7V

TEMPERATURE (°C)		V_TAO (mV)		LOCAL SLOPE (mV/°C)
TEMPERATURE (°C)	MIN	TYP	MAX	LOCAL SLOPE (mV/°C)
-55	1373.576	1375.219	1376.862	-4.958
-50	1348.990	1350.441	1351.892	-4.976
-40	1299.270	1300.593	1301.917	-5.002
-30	1249.242	1250.398	1251.555	-5.036
-20	1198.858	1199.884	1200.910	-5.066
-10	1148.145	1149.070	1149.995	-5.108
0	1097.151	1097.987	1098.823	-5.121
10	1045.900	1046.647	1047.394	-5.134
20	994.367	995.050	995.734	-5.171
30	942.547	943.227	943.902	-5.194
40	890.500	891.178	891.857	-5.217
50	838.097	838.882	839.668	-5.241
60	785.509	786.360	787.210	-5.264
70	732.696	733.608	734.520	-5.285
80	679.672	680.654	681.636	-5.306
90	626.435	627.490	628.545	-5.327
100	572.940	574.117	575.293	-5.347
110	519.312	520.551	521.789	-5.368
120	465.410	466.760	468.110	-5.391
130	411.288	412.739	414.189	-5.430
140	356.458	358.164	359.871	-5.498
150	300.815	302.785	304.756	-5.538

8.7 Switching Characteristics

Limits apply for T_A = T_J = T_MIN to T_MAX and VDD of 2.00V to 5.5V and VDD ≥ V_TAO + 1V, unless otherwise noted.

PARAMETER		TEST CONDITIONS	TYP	MAX	UNIT
t_POWER	Power-on Time to 99% of final voltage value	CL=0 pF to 1100 pF; VDD connected T_ON	0.6	1	ms
t_{T_ON}	T_ON Time to 99% of final voltage value (note dependent on RON and C load)	CL=150pF	30	500	µs
C_{T_ON}	T_ON Digital Input Capacitance		2.2		pF

Figure 1. Definition of t_{T_ON}

LMT70 LMT70A tPOWER_waveform_SNIS187.gif

Figure 2. Definition of t_POWER

8.8 Typical Performance Characteristics

VDD=2.7V
using LUT (Look-Up Table) and linear interporlation for conversion of voltage to temperature

Figure 3. Temperature Accuracy

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 5. Accuracy Histogram at -40°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 7. Accuracy Histogram at -10°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 9. Accuracy Histogram at 50°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 11. Accuracy Histogram at 110°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 13. Accuracy Histogram at 150°C

Figure 15. IDD vs Temperature at Various VDD

LMT70 LMT70A VDD_ON_Waveform_SNIS187.gif

Conditions:		Various VDD and C_LOAD

Figure 17. Start-up Response

	VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 19. LMT70A Matching of Adjacent Units on Tape and Reel

Figure 21. Minimum Recommended Supply Voltage Temperature Sensitivity


VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 4. Accuracy Histogram at -55°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 6. Accuracy Histogram at –20°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 8. Accuracy Histogram at 30°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 10. Accuracy Histogram at 90°C

VDD=2.7V
using LUT table for conversion of voltage to temperature

Figure 12. Accuracy Histogram at 120°C

VDD=2.7V

Figure 14. TAO first order transfer function slope vs temperature

At 30°C

Figure 16. TAO Line Regulation

LMT70 LMT70A TON_Waveform_3V_SNIS187.gif

	VDD=3.3V
	Top trace is T_ON
Bottom trace is TAO

Figure 18. TAO Response to T_ON

at various temperatures

Figure 20. Line Regulation Temperature Variation: V_TAO vs Supply Voltage

Figure 22. Output Noise vs Frequency

9 Detailed Description

9.1 Overview

The LMT70 is a precision analog output temperature sensor. It includes an output switch that is controlled by the T_ON digital input. The output switch enables the multiplexing of several devices onto a single ADC input thus expanding on the ADC input multiplexer capability.

The temperature sensing element is comprised of simply stacked BJT base emitter junctions that are biased by a current source. The temperature sensing element is then buffered by a precision amplifier before being connected to the output switch. The output amplifier has a simple class AB push-pull output stage that enables the device to easily source and sink current.

9.2 Functional Block Diagram

9.3 Feature Description

9.3.1 Temperature Analog Output (TAO)

The TAO push-pull output provides the ability to sink and source current. This is beneficial when, for example, driving dynamic loads like an input stage on an analog-to-digital converter (ADC). In these applications the source current is required to quickly charge the input capacitor of the ADC. See the Typical Application section for more discussion of this topic. The LMT70 is ideal for this and other applications which require strong source or sink current.

9.3.1.1 LMT70 Output Transfer Function

The LMT70 output voltage transfer function appears to be linear, but upon close inspection it can be seen that it is truly not linear and can be better described by a second or third order transfer function equation.

LMT70 LMT70A LMT70_TransferFuctionCurve_SNIS187.png

Figure 23. LMT70 Output Transfer Function

9.3.1.1.1 First Order Transfer Function

A first order transfer function can be used to calculate the temperature LMT70 is sensing but over a wide temperature range it is the least accurate method. An equation can be easily generated using the LUT (Look-Up Table) information found in Electrical Characteristics Temperature Lookup Table (LUT) .

Over a narrow 10°C temperature range a linear equation will yield very accurate results. It is actually recommended that over a 10°C temperature range linear interpolation be used to calculate the temperature the device is sensing. When this method is used the accuracy minimum and maximum specifications would meet the values given in Figure 3.

For example the first order equation between 20°C and 30°C can be generated using the typical output voltage levels as given in Electrical Characteristics Temperature Lookup Table (LUT) and partially repeated here for reference from 20°C to 50°C:

Table 1. Output Voltage LUT

Temperature (°C)		V_TAO (mV)		Local Slope (mV/°C)
Temperature (°C)	MIN	TYP	MAX	Local Slope (mV/°C)
20	994.367	995.050	995.734	-5.171
30	942.547	943.227	943.907	-5.194
40	890.423	891.178	891.934	-5.217
50	838.097	838.882	839.668	-5.241

First calculate the slope:

m =(T1 – T2) ÷ [(V_TAO (T1) – V_TAO (T2)]

m = (20°C - 30°C) ÷ (995.050 mV – 943.227 mV)

m = –0.193 °C/mV

Then calculate the y intercept b:

b = (T1) – (m × V_TAO(T1))

b = 20°C – (–0.193 °C/mV × 995.050 mV)

b = 212.009°C

Thus the final equation used to calculate the measured temperature (T_M) in the range between 20°C and 30°C is:

T_M = m × V_TAO + b

T_M = –0.193 °C/mV × V_TAO + 212.009°C

where V_TAO is in mV and T_M is in °C.

9.3.1.1.2 Second Order Transfer Function

A second order transfer function can give good results over a wider limited temperature range. Over the full temperature range of -55°C to +150°C a single second order transfer function will have increased error at the temperature extremes. Using least squares sum method a best fit second order transfer function was generated using the values in Electrical Characteristics Temperature Lookup Table (LUT):

T_M = a (V_TAO)²+ b (V_TAO) + c

where:

	Best fit for -55°C to 150°C	Best fit for -10°C to 110°C
a	-8.451576E-06	-7.857923E-06
b	-1.769281E-01	-1.777501E-01
c	2.043937E+02	2.046398E+02

and V_TAO is in mV and T_M is in °C.

9.3.1.1.3 Third Order Transfer Function

Over a wide temperature range the most accurate single equation is a third order transfer function. Using least squares sum method a best fit third order transfer function was generated using the values in Figure 3:

T_M = a (V_TAO)³ + b (V_TAO)² + c(V_TAO) + d

where:

	Best fit for -55°C to 150°C	Best fit for -10°C to 110°C
a	-1.064200E-09	-1.809628E-09
b	-5.759725E-06	-3.325395E-06
c	-1.789883E-01	-1.814103E-01
d	2.048570E+02	2.055894E+02

and V_TAO is in mV and T_M is in °C.

9.3.1.2 LMT70A TAO Matching

In order to meet the matching specification of the LMT70A, two units must be picked from adjacent positions from one tape and reel. If PCB rework is required, involving the LMT70A, then the pair of the LMT70A matched units must be replaced. Matching features (which include, without limitation, electrical matching characteristics of adjacent Components as they are delivered in original packaging from TI) are warranted solely to the extent that the purchaser can demonstrate to TI’s satisfaction that the particular Component(s) at issue were adjacent in original packaging as delivered by TI. Customers should be advised that the small size of these components means they are not individually traceable at the unit level and it may be difficult to establish the original position of the Components once they have been removed from that original packaging as delivered by TI.

9.3.1.3 TAO Noise Considerations

A load capacitor on TAO pin can help to filter noise.

For noisy environments, TI recommends at minimum 100 nF supply decoupling capacitor placed close across VDD and GND pins of LMT70.

9.3.1.4 TAO Capacitive Loads

TAO handles capacitive loading well. In an extremely noisy environment, or when driving a switched sampling input on an ADC, it may be necessary to add some filtering to minimize noise coupling. Without any precautions, the V_TAO can drive a capacitive load less than or equal to 1 nF as shown in Figure 24. For capacitive loads greater than 1 nF, a series resistor is required on the output, as shown in Figure 25, to maintain stable conditions.

LMT70 LMT70A CapacitiveLoading1_SNIS187.gif

Figure 24. LMT70 No Isolation Resistor Required

LMT70 LMT70A CapacitiveLoading2_SNIS187.gif

Figure 25. LMT70 With Series Resistor for Capacitive Loading Greater than 1 nF

Table 2. C_LOAD and R_S Values of Figure 25

C_LOAD	Minimum R_S
1.1 to 90 nF	3 kΩ
90 to 900 nF	1.5 kΩ
0.9 μF	750 Ω

9.3.2 T_ON Digital Input

The T_ON digital input enables and disables the analog output voltage presented at the TAO pin by controlling the state of the internal switch that is in series with the internal temperature sensor circuitry output. When T_ON is driven to a logic "HIGH" the temperature sensor output voltage is present on the TAO pin. When T_ON is set to a logic "LOW" the TAO pin is set to a high impedance state.

9.3.3 Light Sensitivity

Although the LMT70 package has a protective backside coating that reduces the amount of light exposure on the die, unless it is fully shielded, ambient light will still reach the active region of the device from the side of the package. Depending on the amount of light exposure in a given application, an increase in temperature error should be expected. In circuit board tests under ambient light conditions, a typical increase in error may not be observed and is dependent on the angle that the light approaches the package. The LMT70 is most sensitive to IR radiation. Best practice should include end-product packaging that provides shielding from possible light sources during operation.

9.4 Device Functional Modes

The LMT70 is a simple precise analog output temperature sensor with a switch in series with its output. It has only two functional modes: output on or output off.

10 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.

10.1 Application Information

The LMT70 analog output temperature sensor is an ideal device to connect to an integrated 12-Bit ADC such as that found in the MSP430 microcontroller family.

Applications for the LMT70 included but are not limited to: IoT based temperature sensor nodes, medical fitness equipment (e.g. thermometers, fitness/smart bands or watches, activity monitors, human body temperature monitor), Class AA or lower RTD replacement, precision NTC or PTC thermistor replacement, instrumentation temperature compensation, metering temperature compensation (e. g. heat cost allocator, heat meter).

10.2 Typical Application

Figure 26. Typical Application Schematic

Most CMOS ADCs found in microcontrollers and ASICs have a sampled data comparator input structure. When the ADC charges the sampling cap, it requires instantaneous charge from the output of the analog source such as the LMT70 temperature sensor and many op amps. This requirement is easily accommodated by the addition of a capacitor (C_FILTER) or the extension of the ADC acquisition time thus slowing the ADC sampling rate. The size of C_FILTER depends on the size of the sampling capacitor and the sampling frequency. Since not all ADCs have identical input stages, the charge requirements will vary. The general ADC application shown in Figure 27 is an example only. The application in Figure 26 was actually tried and the extension of the MSP430 12-Bit ADC acquisition time was all that was necessary in order to accommodate the LMT70's output stage drive capability.

Figure 27. Suggested Connection to a Sampling Analog-to-Digital Converter Input Stage

10.2.1 Design Requirements

The circuit show in Figure 26 will support the design requirements as shown in Table 3.

Table 3. Design Requirements

PARAMETER	TARGET SPECIFICATION
Temperature Range	-40°C to +150°C LMT70, -40°C to +85°C for MSP430
Accuracy	±0.2°C typical over full temperature range
VDD	2.2V to 3.6V with typical of 3.0V
IDD	12µA

10.2.2 Detailed Design Procedure

10.2.2.1 Temperature Algorithm Selection

Of the three algorithms presented in this datasheet, linear interpolation, second order transfer function or third order transfer function, the one selected will be determined by the users microcontroller resources and the temperature range that will be sensed. Therefore, a comparison of the expected accuracy from the LMT70 is given here. The following curves show effect on the accuracy of the LMT70 when using each of the different algorithms/equations given in LMT70 Output Transfer Function. The first curve (Figure 28) shows the performance when using linear interpolation of the LUT values shown in Electrical Characteristics Temperature Lookup Table (LUT) of every 10°C and provides the best performance. Linear interpolation of the LUT values shown in Electrical Characteristics Temperature Lookup Table (LUT) is used to determine the LMT70 min/max accuracy limits as shown in the Electrical Characteristics and the red lines of Figure 28. The other lines in the middle of Figure 28 show independent device performance. The green limit lines, shown in the subsequent figures, apply for the specific equation used to convert the output voltage of the LMT70 to temperature. The equations are shown under each figure for reference purposes. The green lines show the min/max limits when set in a similar manner to the red limit lines of Figure 28. The limits shown in red for Figure 28 are repeated in all the figures of this section for comparison purposes.

Temp (°C)		V_TAO (mV)		Local Slope (mV/°C)
Temp (°C)	MIN	TYP	MAX	Local Slope (mV/°C)
20	994.367	995.050	995.734	-5.171
30	942.547	943.227	943.907	-5.194
40	890.423	891.178	891.934	-5.217
50	838.097	838.882	839.668	-5.241

Figure 28. LMT70 Performance Using LUT and Linear Interpolation

T_M = -1.809628E-09 (V_TAO)³ – 3.325395E-06 (V_TAO)² – 1.814103E-01(V_TAO) + 2.055894E+02

Figure 30. Using Third Order Transfer Function Best Fit -10°C to +110°C

T_M = -7.857923E-06 (V_TAO)² – 1.777501E-01 (V_TAO) + 2.046398E+02

Figure 32. Using Second Order Transfer Function Best Fit -10°C to 110°C

T_M = -1.064200E-09 (V_TAO)³ – 5.759725E-06 (V_TAO)² – 1.789883E-01(V_TAO) + 2.048570E+02

Figure 29. Using Third Order Transfer Function Best Fit -55°C to +150°C

T_M = -8.451576E-06 (V_TAO)²– 1.769281E-01 (V_TAO) + 2.043937E+02

Figure 31. Using Second Order Transfer Function Best Fit -55°C to 150°C

10.2.2.2 ADC Requirements

The ADC resolution and its specifications as well as reference voltage and its specifications will determine the overall system accuracy that you can obtain. For this example the 12-bit SAR ADC found in the MSP430 was used as well as it's integrated reference. At first glance the specifications may not seem to be precise enough to actually be used with the LMT70 but the MSP430 ADC and integrated reference errors are actually measured during production testing of the MSP430. Values are then provided to user for software calibration. These calibration values are located in the MSP430A device descriptor tag-length-value (TLV) structure and found in the device-specific datasheet. The MSP430 Users Guide includes information on how to use these calibration values to calibrate the ADC reading. The specific values used to calibrate the ADC readings are: CAL_ADC_15VREF_FACTOR, CAL_ADC_GAIN_FACTOR and CAL_ADC_OFFSET.

10.2.3 Finer Resolution LUT

The following table is given for reference only and not meant to be used for calculation purposes.

Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)	Temp (°C)	V_TAO (mV)
Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP	Temp (°C)	TYP
		-30	1250.398	0	1097.987	30	943.227	60	786.360	90	627.490	120	466.760	150	302.785
		-29	1244.953	1	1092.532	31	937.729	61	780.807	91	621.896	121	460.936
		-28	1239.970	2	1087.453	32	932.576	62	775.580	92	616.603	122	455.612
		-27	1234.981	3	1082.370	33	927.418	63	770.348	93	611.306	123	450.280
		-26	1229.986	4	1077.282	34	922.255	64	765.113	94	606.006	124	444.941
-55	1375.219	-25	1224.984	5	1072.189	35	917.087	65	759.873	95	600.701	125	439.593
-54	1370.215	-24	1219.977	6	1067.090	36	911.915	66	754.628	96	595.392	126	434.238
-53	1365.283	-23	1214.963	7	1061.987	37	906.738	67	749.380	97	590.079	127	428.875
-52	1360.342	-22	1209.943	8	1056.879	38	901.556	68	744.127	98	584.762	128	423.504
-51	1355.395	-21	1204.916	9	1051.765	39	896.370	69	738.870	99	579.442	129	418.125
-50	1350.441	-20	1199.884	10	1046.647	40	891.178	70	733.608	100	574.117	130	412.739
-49	1345.159	-19	1194.425	11	1041.166	41	885.645	71	728.055	101	568.504	131	406.483
-48	1340.229	-18	1189.410	12	1036.062	42	880.468	72	722.804	102	563.192	132	401.169
-47	1335.293	-17	1184.388	13	1030.952	43	875.287	73	717.550	103	557.877	133	395.841
-46	1330.352	-16	1179.361	14	1025.838	44	870.100	74	712.292	104	552.557	134	390.499
-45	1325.405	-15	1174.327	15	1020.720	45	864.909	75	707.029	105	547.233	135	385.144
-44	1320.453	-14	1169.288	16	1015.596	46	859.713	76	701.762	106	541.905	136	379.775
-43	1315.496	-13	1164.242	17	1010.467	47	854.513	77	696.491	107	536.573	137	374.393
-42	1310.534	-12	1159.191	18	1005.333	48	849.307	78	691.217	108	531.236	138	368.997
-41	1305.566	-11	1154.134	19	1000.194	49	844.097	79	685.937	109	525.895	139	363.587
-40	1300.593	-10	1149.070	20	995.050	50	838.882	80	680.654	110	520.551	140	358.164
-39	1295.147	-9	1143.654	21	989.583	51	833.343	81	675.073	111	514.886	141	351.937
-38	1290.202	-8	1138.599	22	984.450	52	828.141	82	669.803	112	509.557	142	346.508
-37	1285.250	-7	1133.540	23	979.313	53	822.934	83	664.528	113	504.223	143	341.071
-36	1280.291	-6	1128.476	24	974.171	54	817.723	84	659.250	114	498.885	144	335.625
-35	1275.326	-5	1123.407	25	969.025	55	812.507	85	653.967	115	493.542	145	330.172
-34	1270.353	-4	1118.333	26	963.875	56	807.287	86	648.680	116	488.195	146	324.711
-33	1265.375	-3	1113.254	27	958.720	57	802.062	87	643.389	117	482.843	147	319.241
-32	1260.389	-2	1108.170	28	953.560	58	796.832	88	638.094	118	477.486	148	313.764
-31	1255.397	-1	1103.081	29	948.396	59	791.598	89	632.794	119	472.125	149	308.279

10.2.4 Application Curves

The LMT70 performance using the MSP430 with integrated 12-bit ADC is shown in Figure 33. This curve includes the error of the MSP430 integrated 12-bit ADC and reference as shown in the schematic Figure 26. The MSP430 was kept at room temperature and the LMT70 was submerged in a precision temperature calibration oil bath. A calibrated temperature probe was used to monitor the temperature of the oil. As can be seen in Figure 33 the combined performance on the MSP430 and the LMT70 is better than 0.12°C for the entire -40°C to +150°C temperature range. The only calibration performed was with software using the MSP430A device descriptor tag-length-value (TLV) calibration values for ADC and VREF error.

Figure 33. LMT70 with MSP430 typical performance

10.3 System Examples

Figure 34. Multiple LMT70s connected to one 12-bit ADC channel on an MSP430

Figure 35. Multiple LMT70s connected to a slope ADC for high resolution