ZHCSGK9A April 2017  – July 2017 TPS22971

PRODUCTION DATA. 

  1. 特性
  2. 应用
  3. 说明
  4. 修订历史记录
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1Absolute Maximum Ratings
    2. 6.2ESD Ratings
    3. 6.3Recommended Operating Conditions
    4. 6.4Thermal Information
    5. 6.5Electrical Characteristics
    6. 6.6Switching Characteristics
    7. 6.7Typical DC Characteristics
    8. 6.8Typical AC Characteristics
  7. Parameter Measurement Information
  8. Detailed Description
    1. 8.1Overview
    2. 8.2Functional Block Diagram
    3. 8.3Feature Description
      1. 8.3.1On and Off Control
      2. 8.3.2Controlled Turn-On
      3. 8.3.3Power Good (PG)
      4. 8.3.4Quick Output Discharge (QOD)
    4. 8.4Device Functional Modes
  9. Application and Implementation
    1. 9.1Application Information
      1. 9.1.1Thermal Consideration
      2. 9.1.2PG Pull Up Resistor
      3. 9.1.3Power Sequencing
    2. 9.2Typical Application
      1. 9.2.1Design Requirements
      2. 9.2.2Detailed Design Procedure
        1. 9.2.2.1Maximum Voltage Drop and On-Resistance
        2. 9.2.2.2Managing Inrush Current
      3. 9.2.3Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1Layout Guidelines
    2. 11.2Layout Example
  12. 12器件和文档支持
    1. 12.1文档支持
      1. 12.1.1相关文档
    2. 12.2接收文档更新通知
    3. 12.3社区资源
    4. 12.4商标
    5. 12.5静电放电警告
    6. 12.6Glossary
  13. 13机械、封装和可订购信息

Detailed Description

Overview

The TPS22971 is a single channel, 3-A load switch in a small, space-saving WCSP-8 package. This device implements a low resistance N-channel MOSFET with a controlled rise time for applications that need to limit the inrush current.

The controlled rise time for the device greatly reduces inrush current caused by large bulk load capacitances, thereby reducing or eliminating power supply droop. The adjustable slew rate through CT provides the design flexibility to trade off the inrush current and power up timing requirements. Integrated PG indicator notifies the system about the status of the load switch to facilitate seamless power sequencing.

This device is also designed to have very low leakage current during off state, which prevents downstream circuits from pulling high standby current from the supply. Integrated control logic, driver, power supply, and output discharge FET eliminates the need for additional external components, which reduces solution size and bill of materials (BOM) count.

Functional Block Diagram

TPS22971 Functional-Block-Diagram.gif

Feature Description

On and Off Control

The ON pin controls the state of the switch. Asserting ON high enables the switch. ON has a low threshold, making it capable of interfacing with low-voltage signals. The ON pin is compatible with standard GPIO logic. It can be used with any microcontroller with 1.2-V, 1.8-V, 2.5-V or 3.3-V GPIOs. This pin does not have an internal bias and must not be left floating for proper functionality.

Controlled Turn-On

The TPS22971 has controlled Turn-On for inrush current control. A capacitor to GND on the CT pin adjusts the slew rate. For a given input voltage and desired slew rate, Equation 1 can be used to find the required CT value. For calculated CT values less than 220 pF, use 0 pF instead when solving for tON and tPG,ON.

Equation 1. TPS22971 tps22971x-equation-01.gif

where

  • CT is the capacitor on the CT pin (in pF)
  • VIN is the input voltage (in V)
  • SR is the desired slew rate (in V/µs)

The CT value determined in Equation 1 can be used to find the total Turn-On time, tON, in Equation 2 or Equation 3 depending on VIN.

Equation 2. TPS22971 tps22971x-equation-02.gif
Equation 3. TPS22971 tps22971x-equation-03.gif

where

  • tON is the Turn-On time (in µs)
  • CT is the capacitor on the CT pin (in pF)
  • VIN is the input voltage (in V)

Power Good (PG)

The TPS22971 has a power good (PG) output signal to indicate the gate of the pass FET is driven high and the switch is fully on (full load ready). The signal is an active high and open drain output which can be connected to a voltage source through an external pull up resistor, RPU. This voltage source can be VOUT from the TPS22971 or another external voltage. Equation 4 and Equation 5 show the approximate equation for the relationship between CT setting, VIN and PG Turn-On time (tPG,ON):

Equation 4. TPS22971 tps22971x-equation-04.gif
Equation 5. TPS22971 tps22971x-equation-05.gif

where

  • tPG,ON is the PG Turn-On time (in µs)
  • VIN is the input voltage (in V)
  • CT is the capacitance value on the CT pin (in pF)

Quick Output Discharge (QOD)

The TPS22971 includes a QOD feature. When the switch is disabled, a discharge resistor is connected between VOUT and GND. This resistor has a typical value of 150 Ω and prevents the output from floating while the switch is disabled. The QOD pull-down resistance can vary with input voltage and temperature, see Figure 4.

Device Functional Modes

Table 1 lists the functional modes for the TPS22971.

Table 1. Function Table

TPS22971
ON-PinVIN to VOUT VOUT to GNDPG to GND
Below VILOFF ONON
Above VIHONOFFOFF