TPS22975 5.7V、6A、导通电阻为 16mΩ 的负载开关
- ZHCSF80B May 2016 – September 2017 TPS22975
  
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TPS22975 5.7V、6A、导通电阻为 16mΩ 的负载开关

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1 特性

集成单通道负载开关
输入电压范围：0.6V 至 V_BIAS
V_BIAS 电压范围：2.5V 至 5.7V
导通电阻 (R_ON)
- R_ON = 16m（VIN = 0.6V 到 5.7V，
  V_BIAS = 5.7V 时的典型值）
6A 最大持续开关电流
低静态电流
- 37µA（V_IN = V_BIAS = 5V 时的典型值）
低控制输入阈值支持使用
1.2V、1.8V、2.5V、3.3V 逻辑器件
可配置的上升时间
热关断
快速输出放电 (QOD)（可选）
带有散热焊盘的小外形尺寸无引线 (SON) 8 引脚封装
经测试，静电放电 (ESD) 性能符合 JESD 22 规范
- 2000V 人体模型 (HBM) 和 1000V 带电器件模型 (CDM)

2 应用

Ultrabook™
笔记本电脑和上网本
平板电脑
消费类电子产品
机顶盒和家庭网关
电信系统
固态硬盘 (SSD)

3 说明

TPS22975 产品系列包含两个器件：TPS22975 和 TPS22975N。每个器件都是一款单通道负载开关，可提供可配置的上升时间来尽量减小浪涌电流。此器件包括一个 N 通道金属氧化物半导体场效应晶体管 (MOSFET)，可在 0.6 V 至 5.7V 的输入电压范围内运行并可支持 6A 的最大持续电流。此开关由一个开/关输入 (ON) 控制，此输入能够直接连接低电压控制信号。TPS22975 包含一个可选 230Ω 片上负载电阻，用于在此开关关断时进行快速输出放电。

TPS22975 采用小型，节省空间的 2mm × 2mm 8 引脚 SON 封装 (DSG)，集成的散热焊盘允许该器件产生较高的功率耗散。该器件在自然通风环境下的额定运行温度范围为 –40°C 至 +105°C。

器件信息⁽¹⁾

器件型号	封装	封装尺寸（标称值）
TPS22975 TPS22975N	WSON (8)	2.00mm x 2.00mm

要了解所有可用封装，请参阅数据表末尾的可订购产品附录。

简化电路原理图

TPS22975 application_circuit_02_SLVSDD0.gif

导通电阻与输入电压间的关系

V_BIAS = 5V，I_VOUT = –200mA

4 修订历史记录

Changes from A Revision (June 2016) to B Revision

Updated V_IH in Recommended Operating ConditionsGo

Changes from * Revision (May 2016) to A Revision

器件状态，从产品预览改为量产数据Go

5 Device Comparison Table

DEVICE	R_ON AT V_IN = V_BIAS = 5 V (TYPICAL)	QUICK-OUTPUT DISCHARGE	MAXIMUM OUTPUT CURRENT	ENABLE
TPS22975	16 mΩ	Yes	6 A	Active high
TPS22975N	16 mΩ	No	6 A	Active high

6 Pin Configuration and Functions

DSG Package

8-Pin (WSON)

Top View

DSG Package

8-Pin (WSON)

Bottom View

Pin Functions

PIN		I/O	DESCRIPTION
NO.	NAME	I/O	DESCRIPTION
1	VIN	I	Switch input. Input bypass capacitor recommended for minimizing V_IN dip. Must be connected to Pin 1 and Pin 2. See the Application and Implementation section for more information
2	VIN	I
3	ON	I	Active high switch control input. Do not leave floating
4	VBIAS	I	Bias voltage. Power supply to the device. Recommended voltage range for this pin is 2.5 V to 5.7 V. See the Application and Implementation section for more information
5	GND	—	Device ground
6	CT	O	Switch slew rate control. Can be left floating. See the Adjustable Rise Time section under Feature Description for more information
7	VOUT	O	Switch output
8	VOUT	O	Switch output
—	Thermal Pad	—	Thermal pad (exposed center pad) to alleviate thermal stress. Tie to GND. See the Layout Example section for layout guidelines

7 Specifications

7.1 Absolute Maximum Ratings

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

		MIN	MAX	UNIT
V_IN	Input voltage	–0.3	6	V
V_OUT	Output voltage	–0.3	6	V
V_BIAS	Bias voltage	–0.3	6	V
V_ON	On voltage	–0.3	6	V
I_MAX	Maximum continuous switch current		6	A
I_PLS	Maximum pulsed switch current, pulse < 300 µs, 2% duty cycle		8	A
T_J	Maximum junction temperature		125	°C
T_stg	Storage temperature	–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.

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

			MIN	MAX	UNIT
V_IN	Input voltage		0.6	V_BIAS	V
V_BIAS	Bias voltage		2.5	5.7	V
V_ON	ON voltage		0	5.7	V
V_OUT	Output voltage			V_IN	V
V_IH	High-level input voltage, ON	V_BIAS = 2.5 V to 5 V, T_A< 85°C	1.05	5.7	V
		V_BIAS = 2.5 V to 5 V, T_A< 105°C	1.1	5.7
		V_BIAS = 5 V to 5.7 V, T_A< 105°C	1.2	5.7
V_IL	Low-level input voltage, ON	V_BIAS = 2.5 V to 5.7 V	0	0.5	V
C_IN	Input capacitor		1⁽¹⁾		µF
T_A	Operating free-air temperature⁽¹⁾⁽²⁾		–40	105	°C

(1) See the Application Information section.

(2) In applications where high power dissipation and-or poor package thermal resistance is present, the maximum ambient temperature may have to be derated and device lifetime may be affected. Maximum ambient temperature (T_A(max)) is dependent on the maximum operating junction temperature (T_J(max)), the maximum power dissipation of the device in the application (P_D(max)), and the junction-to-ambient thermal resistance of the part-package in the application (θ_JA), and can be approximated by the following equation: T_A _(max) = T_J(max) – (θ_JA × P_D(max)).

7.4 Thermal Information

THERMAL METRIC⁽¹⁾		TPS22975	UNIT
		DSG (WSON)
		8 PINS
R_θJA	Junction-to-ambient thermal resistance	74.8	°C/W
R_θJC(top)	Junction-to-case (top) thermal resistance	81	°C/W
R_θJB	Junction-to-board thermal resistance	44.7	°C/W
ψ_JT	Junction-to-top characterization parameter	3.9	°C/W
ψ_JB	Junction-to-board characterization parameter	45.1	°C/W
R_θJC(bot)	Junction-to-case (bottom) thermal resistance	16.4	°C/W

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

7.5 Electrical Characteristics—V_BIAS = 5 V

Unless otherwise noted, the specifications in the following table applies where V_BIAS = 5 V. Typical values are for T_A = 25 °C.

PARAMETER		TEST CONDITIONS		T_A	TYP	MAX	UNIT
POWER SUPPLIES AND CURRENTS
I_{Q, VBIAS}	V_BIASquiescent current	I_OUT = 0 A, V_IN = V_ON = 5 V		–40°C to +105°C	37	45	µA
I_{SD, VBIAS}	V_BIAS shutdown current	V_ON = V_OUT = 0 V		–40°C to +105°C		2.3	µA
I_{SD, VIN}	V_IN off-state supply current	V_ON = V_OUT = 0 V	V_IN = 5 V	–40°C to +85°C	0.005	5	µA
			V_IN = 5 V	–40°C to +105°C		10
			V_IN = 3.3 V	–40°C to +85°C	0.002	1.5
			V_IN = 3.3 V	–40°C to +105°C		3.5
			V_IN = 1.8 V	–40°C to +85°C	0.002	1
			V_IN = 1.8 V	–40°C to +105°C		2
			V_IN = 0.6 V	–40°C to +85°C	0.001	0.5
			V_IN = 0.6 V	–40°C to +105°C		1
I_ON	On-pin input leakage current	V_ON = 5.5 V		–40°C to +105°C		0.1	µA
RESISTANCE CHARACTERISTICS
R_ON	On-resistance	I_OUT = –200 mA	V_IN = 5 V	25°C	16	19	mΩ
				–40°C to +85°C		23
				–40°C to +105°C		25
			V_IN = 3.3 V	25°C	16	19
				–40°C to +85°C		23
				–40°C to +105°C		25
			V_IN = 1.8 V	25°C	16	19
				–40°C to +85°C		23
				–40°C to +105°C		25
			V_IN = 1.5 V	25°C	16	19
				–40°C to +85°C		23
				–40°C to +105°C		25
			V_IN = 1.05 V	25°C	16	19
				–40°C to +85°C		23
				–40°C to +105°C		25
			V_IN = 0.6 V	25°C	16	19
				–40°C to +85°C		23
				–40°C to +105°C		25
V_{ON, H}_YS	On-pin hysteresis	V_IN = 5 V		25°C	120		mV
R_PD ⁽¹⁾	Output pulldown resistance	V_IN = 5 V, V_ON = 0 V		–40°C to +105°C	230	300	Ω
T_SD	Thermal shutdown	Junction temperature rising			160		°C
T_{SD, HYS}	Thermal shutdown hysteresis	Junction temperature falling			20		°C

(1) TPS22975 only

7.6 Electrical Characteristics—V_BIAS = 2.5 V

Unless otherwise noted, the specifications in the following table applies where V_BIAS = 2.5 V. Typical values are for T_A = 25 °C.

PARAMETER		TEST CONDITIONS		T_A	TYP	MAX	UNIT
POWER SUPPLIES AND CURRENTS
I_{Q, VBIAS}	V_BIASquiescent current	I_OUT = 0 mA, V_IN = V_ON = 2.5 V		–40°C to +105°C	14	20	µA
I_{SD, VBIAS}	V_BIAS shutdown current	V_ON = V_OUT = 0 V		–40°C to +105°C		1	µA
I_{SD, VIN}	V_IN off-state supply current	V_ON = V_OUT = 0 V	V_IN = 2.5 V	–40°C to +85°C	0.005	1.3	µA
			V_IN = 2.5 V	–40°C to +105°C		2.6
			V_IN = 1.8 V	–40°C to +85°C	0.002	1
			V_IN = 1.8 V	–40°C to +105°C		2
			V_IN = 1.05 V	–40°C to +85°C	0.002	0.8
			V_IN = 1.05 V	–40°C to +105°C		1.5
			V_IN = 0.6 V	–40°C to +85°C	0.001	0.5
			V_IN = 0.6 V	–40°C to +105°C		1
I_ON	On-pin input leakage current	V_ON = 5.5 V		–40°C to +105°C		0.1	µA
RESISTANCE CHARACTERISTICS
R_ON	On-resistance	I_OUT = –200 mA	V_IN = 2.5 V	25°C	20	26	mΩ
				–40°C to +85°C		32
				–40°C to +105°C		34
			V_IN = 1.8 V	25°C	18	23
				–40°C to +85°C		29
				–40°C to +105°C		31
			V_IN = 1.5 V	25°C	18	22
				–40°C to +85°C		28
				–40°C to +105°C		30
			V_IN = 1.2 V	25°C	17	22
				–40°C to +85°C		27
				–40°C to +105°C		29
			V_IN = 0.6 V	25°C	17	21
				–40°C to +85°C		26
				–40°C to +105°C		27
V_{ON, HYS}	On-pin hysteresis	V_IN = 2.5 V		25°C	85		mV
R_PD⁽¹⁾	Output pulldown resistance	V_IN = 2.5 V, V_ON = 0 V		–40°C to +105°C	230	330	Ω
T_SD	Thermal shutdown	Junction temperature rising			160		°C
T_{SD, HYS}	Thermal shutdown hysteresis	Junction temperature falling			20		°C

(1) TPS22975 only

7.7 Switching Characteristics

PARAMETER		TEST CONDITION	TYP	UNIT
V_IN = V_BIAS = 5 V, T_A = 25ºC (unless otherwise noted)
t_ON	Turnon time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	1450	µs
t_OFF	Turnoff time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_R	V_OUT rise time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	1750
t_F	V_OUT fall time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_D	ON delay time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	600
V_IN = 0.6 V, V_BIAS = 5 V, T_A = 25ºC (unless otherwise noted)
t_ON	Turnon time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	620	µs
t_OFF	Turnoff time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_R	V_OUT rise time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	280
t_F	V_OUT fall time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_D	ON delay time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	485
V_IN = V_BIAS = 2.5 V, T_A = 25ºC (unless otherwise noted)
t_ON	Turnon time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2180	µs
t_OFF	Turnoff time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_R	V_OUT rise time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2150
t_F	V_OUT fall time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_D	ON delay time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	1120
V_IN = 0.6 V, V_BIAS = 2.5 V, T_A = 25ºC (unless otherwise noted)
t_ON	Turnon time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	1315	µs
t_OFF	Turnoff time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	3
t_R	V_OUT rise time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	650
t_F	V_OUT fall time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	2
t_D	ON delay time	R_L= 10 Ω, C_L = 0.1 µF, C_IN = 1 µF, C_T = 1000 pF, V_ON = 5 V	975

7.8 Typical DC Characteristics

V_IN = V_BIAS	V_ON = 5 V	V_OUT = 0 V

Figure 1. V_BIAS Quiescent Current vs Bias Voltage

V_IN = V_BIAS	V_ON = 0 V	V_OUT = 0 V

Figure 3. V_BIAS Shutdown Current vs Bias Voltage

V_BIAS = 5 V	I_OUT = –200 mA	V_ON = 5 V
Note:	All three R_ON curves have the same values; therefore, only one line is visible.

Figure 5. On-Resistance vs Ambient Temperature

V_BIAS = 5 V	I_OUT = –200 mA	V_ON = 5 V

Figure 7. On-Resistance vs Input Voltage

T_A = 25°C	I_OUT = –200 mA	V_ON = 5 V

Figure 9. On-Resistance vs Bias Voltage

V_BIAS = 5 V	V_ON = 5 V	V_OUT = 0 V

Figure 2. V_BIAS Quiescent Current vs Input Voltage

V_BIAS = 5 V	V_ON = 0 V	V_OUT = 0 V

Figure 4. V_IN Off-State Supply Current vs Input Voltage

V_BIAS = 2.5 V	I_OUT = –200 mA	V_ON = 5 V

Figure 6. On-Resistance vs Ambient Temperature

V_BIAS = 2.5 V	I_OUT = –200 mA	V_ON = 5 V

Figure 8. On-Resistance vs Input Voltage

V_IN = 2.5 V	V_ON = 0 V

Figure 10. Output Pull Down Resistance vs Bias Voltage

7.9 Typical AC Characteristics

T_A = 25°C, C_T = 1000 pF, C_IN = 1 µF, C_L = 0.1 µF, R_L = 10 Ω

V_BIAS = 2.5 V

Figure 11. Delay Time vs Input Voltage

V_BIAS = 2.5 V

Figure 13. Fall Time vs Input Voltage

V_BIAS = 2.5 V

Figure 15. Turnoff Time vs Input Voltage

V_BIAS = 2.5 V

Figure 17. Turnon Time vs Input Voltage

V_BIAS = 2.5 V

Figure 19. Rise Time vs Input Voltage

V_IN = 0.6 V	V_BIAS = 2.5 V

Figure 21. Turnon Response Time

V_IN = 2.5 V	V_BIAS = 2.5 V

Figure 23. Turnon Response Time

V_IN = 0.6 V	V_BIAS = 2.5 V

Figure 25. Turnoff Response Time

V_IN = 2.5 V	V_BIAS = 2.5 V

Figure 27. Turnoff Response Time

V_BIAS = 5 V

Figure 12. Delay Time vs Input Voltage

V_BIAS = 5 V

Figure 14. Fall Time vs Input Voltage

V_BIAS = 5 V

Figure 16. Turnoff Time vs Input Voltage

V_BIAS = 5 V

Figure 18. Turnon Time vs Input Voltage

V_BIAS = 5 V

Figure 20. Rise Time vs Input Voltage

V_IN = 0.6 V	V_BIAS = 5 V

Figure 22. Turnon Response Time

V_IN = 5 V	V_BIAS = 5 V

Figure 24. Turnon Response Time

V_IN = 0.6 V	V_BIAS = 5 V

Figure 26. Turnoff Response Time

V_IN = 5 V	V_BIAS = 5 V

Figure 28. Turnoff Response Time

8 Parameter Measurement Information

A. Rise and fall times of the control signal are 100 ns.

B. Turnoff times and fall times are dependent on the time constant at the load. For the TPS22975, the internal pull-down resistance R_PD is enabled when the switch is disabled. The time constant is (R_PD || R_L) × C_L.

Figure 29. Test Circuit

Figure 30. t_ON and t_OFF Waveforms

9 Detailed Description

9.1 Overview

The TPS22975 device is a single-channel, 6-A load switch in an 8-pin SON package. To reduce the voltage drop in high current rails, the device implements an N-channel MOSFET. The device has a configurable slew rate for applications that require a specific rise-time.

The device prevents downstream circuits from pulling high standby current from the supply by limiting the leakage current of the device when it is disabled. The integrated control logic, driver, power supply, and output discharge FET eliminates the need for any external components, which reduces solution size and bill of materials (BOM) count.

9.2 Functional Block Diagram

9.3 Feature Description

9.3.1 Adjustable Rise Time

A capacitor to GND on the CT pin sets the slew rate. The voltage on the CT pin can be as high as 15 V; therefore, the minimum voltage rating for the CT capacitor must be 30 V for optimal performance. An approximate formula for the relationship between C_T and slew rate when V_BIAS is set to 5 V is shown in Equation 1. This equation accounts for 10% to 90% measurement on V_OUT and does not apply for C_T < 100 pF. Use Table 1 to determine rise times for when C_T = 0 pF.

Equation 1. TPS22975 Equation1_SLVSDD0.gif

where

SR is the slew rate (in µs/V)
C_T is the capacitance value on the CT pin (in pF)
The units for the constant 26 are µs/V. The units for the constant 0.43 are µs/(V × pF).

Rise time can be calculated by multiplying the input voltage by the slew rate. Table 1 contains rise time values measured on a typical device. Rise times shown in Table 1 are only valid for the power-up sequence where V_IN and V_BIAS are already in steady state condition before the ON pin is asserted high.

Table 1. Rise Time t_R vs CT Capacitor

C_T (pF)	RISE TIME (µs) 10% - 90%, C_L = 0.1 µF, C_IN = 1 µF, R_L = 10 Ω, V_BIAS = 5 V⁽¹⁾
C_T (pF)	VIN = 5 V	VIN = 3.3 V	VIN = 1.8 V	VIN = 1.5 V	VIN = 1.2 V	VIN = 1.05 V	VIN = 0.6 V
0	140	105	75	65	60	55	40
220	520	360	215	185	160	140	95
470	970	660	385	330	275	240	155
1000	1750	1190	700	595	495	435	275
2200	3875	2615	1520	1290	1070	940	595
4700	7580	5110	2950	2510	2075	1830	1150
10000	16980	11485	6650	5635	4685	4110	2595

(1) Typical Values at 25°C with a 25-V X7R 10% Ceramic Capacitor on CT

9.3.2 Quick-Output Discharge (QOD) (Optional)

The TPS22975 includes an optional QOD feature. When the switch is disabled, an internal discharge resistance is connected between VOUT and GND to remove the remaining charge from the output. This resistance has a typical value of 230 Ω and prevents the output from floating while the switch is disabled. For best results, it is recommended that the device gets disabled before V_BIAS falls below the minimum recommended voltage.

9.3.3 Thermal Shutdown

Thermal shutdown protects the part from internally or externally generated excessive temperatures. When the device temperature triggers T_SD (typical 160°C), the switch is turned off. The switch automatically turns on again if the temperature of the die drops 20 degrees below the T_SD threshold.

9.4 Device Functional Modes

The Table 2 lists the VOUT pin states as determined by the ON pin.

Table 2. VOUT Connection

ON	TPS22975	TPS22975N
L	GND	Open
H	VIN	VIN

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

10.1.1 ON and OFF Control

The ON pin controls the state of the switch. ON is active high and has a 1.2-V ON-pin enable threshold, making it capable of interfacing with low-voltage signals. The ON pin is compatible with standard GPIO logic thresholds. It can be used with any microcontroller with 1.2 V or higher GPIO voltage. This pin cannot be left floating and must be driven either high or low for proper functionality.

10.1.2 Input Capacitor (C_IN) (Optional)

To limit the voltage drop on the input supply caused by transient inrush currents when the switch turns on into a discharged load capacitor or short-circuit, a capacitor needs to be placed between VIN and GND. A 1-µF ceramic capacitor, C_IN, placed close to the pins, is usually sufficient. Higher values of C_IN can be used to further reduce the voltage drop during high current applications. When switching heavy loads, it is recommended to have an input capacitor about 10 times higher than the output capacitor (C_L) to avoid excessive voltage drop.

10.1.3 Output Capacitor (C_L) (Optional)

Because of the integrated body diode in the NMOS switch, a C_I_N greater than C_L is highly recommended. A C_L greater than C_IN can cause V_OUT to exceed V_IN when the system supply is removed. This could result in current flow through the body diode from V_OUT to V_IN. A C_IN to C_L ratio of 10 to 1 is recommended for minimizing V_IN dip caused by inrush currents during startup; however, a 10 to 1 ratio for capacitance is not required for proper functionality of the device. A ratio smaller than 10 to 1 (such as 1 to 1) could cause slightly more V_IN dip upon turn-on because of inrush currents. This can be mitigated by increasing the capacitance on the CT pin for a longer rise time (see the Adjustable Rise Time section).

10.2 Typical Application

For optimal R_ON performance, it is recommended to have V_IN ≤ V_BIAS. The device is functional if V_IN > V_BIAS but it exhibits R_ON greater than what is listed in the Electrical Characteristics—VBIAS = 5 V and Electrical Characteristics—VBIAS = 2.5 V tables.

Figure 31 demonstrates how the TPS22975 can be used to power downstream modules.

Figure 31. Powering a Downstream Module

10.2.1 Design Requirements

DESIGN PARAMETER	EXAMPLE VALUE
V_IN	3.3 V
V_BIAS	5 V
C_L	22 µF
Maximum Acceptable Inrush Current	400 mA

10.2.2 Detailed Design Procedure

10.2.2.1 Inrush Current

When the switch is enabled, the output capacitors must be charged up from 0 V to the set value (3.3 V in this example). This charge arrives in the form of inrush current. Inrush current can be calculated using Equation 2.

Equation 2. Inrush Current = C_L × dV_OUT/dt

where

C_L is the output capacitance
dV_OUT is the change in V_OUT during the ramp up of the output voltage when device is enabled.
dt is the rise time in V_OUT during the ramp up of the output voltage when the device is enabled.

The TPS22975 offers adjustable rise time for VOUT. This feature allows the user to control the inrush current during turnon. The appropriate rise time can be calculated using the design requirements and the inrush current equation as shown in Equation 3.

Equation 3. 400 mA = 22 µF × 3.3 V/dt

The value of dt is given by Equation 4.

Equation 4. dt = 181.5 µs

To ensure an inrush current of less than 400 mA, choose a CT value that yields a rise time of more than 181.5 µs. See the oscilloscope captures in the Application Curves section for an example of how the CT capacitor can be used to reduce inrush current.

10.2.3 Application Curves

V_BIAS = 5 V

V_IN = 3.3 V

C_L = 22 µF

Figure 32. Inrush Current with CT = 0 pF

V_BIAS = 5 V

V_IN = 3.3 V

C_L = 22 µF

Figure 33. Inrush Current with CT = 220 pF