SLVS984B September   2009  – March 2015 TPS22946

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Detection Schemes
        1. 8.3.1.1 Overtemperature Detection
        2. 8.3.1.2 Hard-Short Detection
        3. 8.3.1.3 Moderate Overcurrent Detection
        4. 8.3.1.4 Current Limiting Mode
        5. 8.3.1.5 Fault Reporting
        6. 8.3.1.6 Power-On and Power-Off Sequence
        7. 8.3.1.7 Automatic Disable in Case of Permanent Overcurrent
      2. 8.3.2 Inrush Current Time-out Feature
      3. 8.3.3 CL Control Pin
      4. 8.3.4 Overtemperature Protection
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 On/Off Control
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Trademarks
    2. 12.2 Electrostatic Discharge Caution
    3. 12.3 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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 On/Off Control

The ON pin controls the state of the switch. Activating ON continuously holds the switch in the on state so long as there is no fault. A junction temperature in excess of 150°C overrides the ON control to turn off the switch. ON is active HIGH and has a low threshold making it capable of interfacing with low voltage signals. When the MOSFET is off, the body diode is disabled so no current can flow through it from the input to the output; however, the body diode does not prevent reverse current flowing.

9.2 Typical Application

This application demonstrates how the TPS22946 can be used to power a downstream load that includes a capacitive element (CLOAD).

TPS22946 FrontPageImage.gifFigure 34. Typical Application Schematic

9.2.1 Design Requirements

For this design example, use the following as the input parameters.

Table 4. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
VIN 3.3 V
Output capacitance (CLOAD) 1 µF
VOUT rise time (tR) 50 µs

9.2.2 Detailed Design Procedure

To begin the design process, the designer must know the following:

  • VIN voltage
  • Output capacitance (CLOAD)
  • VOUT rise time (tR)

The TPS22946 has a 435-mA current limit during initial turnon of the switch, Ilimit_inrush. This current limit is higher than the steady-state current limit, ILIM. The purpose of this feature is to allow the inrush current that is caused by charging up the capacitor, CLOAD. To calculate the inrush current that is caused by the capacitor during initial turnon, use the following equation:

Equation 1. TPS22946 Eq2_Iinrush_slvsci4.gif

where

  • IINRUSH = amount of inrush current caused by CLOAD
  • CL = capacitance on VOUT
  • dt = VOUT rise time
  • dVOUT = increase in VOUT during the rise time

Using the given example values, the inrush current in this typical application will be 66-mA:

Equation 2. 66 mA = 1 µF × 3.3 V / 50 µF

The oscilloscope capture in Figure 35 shows the inrush current for the given design example.

9.2.3 Application Curve

TPS22946 tek00001.pngFigure 35. Inrush Current With 1-µF Output Capacitor