SLVSAR3E April   2011  – December 2015 TPS22924B , TPS22924C

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Electrical Characteristics
    6. 7.6  Switching Characteristics, VIN = 3.6 V
    7. 7.7  Switching Characteristics, VIN = 0.9 V
    8. 7.8  Typical Characteristics
    9. 7.9  AC Characteristics (TPS22924B)
    10. 7.10 AC Characteristics (TPS22924C)
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 ON/OFF Control
      2. 9.3.2 Output Capacitor
      3. 9.3.3 Output Pulldown
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 VIN to VOUT Voltage Drop
      2. 10.1.2 Input Capacitor
      3. 10.1.3 Output Capacitor
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Managing Inrush Current
      3. 10.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Links
    2. 13.2 Community Resources
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

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 VIN to VOUT Voltage Drop

The VIN to VOUT voltage drop in the device is determined by the RON of the device and the load current. The RON of the device depends upon the VIN condition of the device. Refer to the RON specification of the device in the Electrical Characteristics table of this datasheet. Once the RON of the device is determined based upon the VIN conditions, use Equation 1 to calculate the VIN to VOUT voltage drop:

Equation 1. ΔV = ILOAD × RON

where

  • ΔV = Voltage drop from VIN to VOUT
  • ILOAD = Load current
  • RON = On-resistance of the device for a specific VIN
  • An appropriate ILOAD must be chosen such that the IMAX specification of the device is not violated.

10.1.2 Input Capacitor

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, CIN, placed close to the pins is usually sufficient. Higher values of CIN can be used to further reduce the voltage drop.

10.1.3 Output Capacitor

A CIN to CL ratio of 10 to 1 is recommended for minimizing VIN dip caused by inrush currents during startup.

10.2 Typical Application

TPS22924B TPS22924C typapp_lvsb46.gif Figure 43. Typical Application

10.2.1 Design Requirements

DESIGN PARAMETER EXAMPLE VALUE
VIN 3.6 V
CL 1 µF
Maximum Acceptable Inrush Current 40 mA

10.2.2 Detailed Design Procedure

10.2.2.1 Managing Inrush Current

When the switch is enabled, the output capacitors must be charged up from 0-V to VIN. This charge arrives in the form of inrush current. Inrush current can be calculated using the following equation:

Equation 2. TPS22924B TPS22924C inrush_eq_slvsb49.gif

where

  • C = Output capacitance
  • TPS22924B TPS22924C dvdt_eq_slvsb49.gif = Output slew rate

The TPS22924B offers a very slow controlled rise time for minimizing inrush current. This device can be selected based upon the maximum acceptable slew rate which can be calculated using the design requirements and the inrush current equation. An output capacitance of 1.0 μF will be used since the amount of inrush increases with output capacitance:

Equation 3. TPS22924B TPS22924C equation1_slvsb46.gif
Equation 4. TPS22924B TPS22924C equation2_slvsb46.gif

To ensure an inrush current of less than 40 mA, a device with a slew rate less than 40 V/ms must be used.

The TPS22924B has a typical rise time of 96 μs at 3.6 V. This results in a slew rate of 37.5 V/ms which meets the above design requirements. For an even lower inrush current requirement, the TPS22924C can be used. The slower rise time of 800 μs at 3.6V results in a slew rate of 4.5 V/ms, well below the design requirements.

10.2.3 Application Curve

TPS22924B TPS22924C TPS22924B Inrush.jpg
VIN = 3.6 V CL = 1 µF TA = 25°C
Figure 44. TPS22924B Inrush Current With a 1 µF Capacitor
TPS22924B TPS22924C TPS22924C Inrush.jpg
VIN = 3.6 V CL = 1 µF TA = 25°C
Figure 45. TPS22924C Inrush Current With a 1 µF Capacitor