SLVSB39A December   2011  – June 2014 TPS22929D

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Switching Characteristics
    7. 7.7 Typical Characteristics
      1. 7.7.1 Typical AC Characteristics
  8. 8 Parametric 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 Pull-Down
      3. 9.3.3 Under-Voltage Lockout
      4. 9.3.4 Reverse Current Protection
    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 Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Thermal Considerations
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Trademarks
    2. 13.2 Electrostatic Discharge Caution
    3. 13.3 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

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

typ_app_lvsb39.gifFigure 22. Typical Application Schematic

10.2.1 Design Requirements

Design Parameter Example Value
VIN 1.5 V to 5 V
CL 0.1 µF to 1 µF
Maximum Acceptable Inrush Current 10 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 voltage. This charge arrives in the form of inrush current. Inrush current can be calculated using the following equation:

Equation 2. inrush_eq_slvsb49.gif

Where,

C = Output capacitance

dvdt_eq_slvsb49.gif = Output slew rate

The TPS22929D 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. dvdt2_eq_slvsb39.gif
Equation 4. dvdt3_eq_slvsb39.gif

To ensure an inrush current of less than 10 mA, a device with a slew rate less than 10 V/ms must be used.

The TPS22929D has a typical rise time of 4500 μs at 3.3 V . This results in a slew rate of 733 mV/ms which meets the above design requirements.

10.2.3 Application Curves

C018_lvsb39.png
VIN = 5 V TA = 25°C CIN = 10 µF
CL = 1 µF RL = 10 Ω
Figure 23. Turn-On Response
C020_lvsb39.png
VIN = 5 V TA = 25°C CIN = 1 µF
CL = 0.1 µF RL = 10 Ω
Figure 25. Turn-On Response Time
C022_lvsb39.png
VIN = 1.5 V TA = 25°C CIN = 10 µF
CL = 1 µF RL = 10 Ω
Figure 27. Turn-On Response Time
C024_lvsb39.png
VIN = 1.5 V TA = 25°C CIN = 1 µF
CL = 0.1 µF RL = 10 Ω
Figure 29. Turn-On Response Time
C019_lvsb39.png
VIN = 5 V TA = 25°C CIN = 10 µF
CL = 1 µF RL = 10 Ω
Figure 24. Turn-Off Response
C021_lvsb39.png
VIN = 5 V TA = 25°C CIN = 1 µF
CL = 0.1 µF RL = 10 Ω
Figure 26. Turn-Off Response Time
C023_lvsb39.png
VIN = 1.5 V TA = 25°C CIN = 10 µF
CL = 1 µF RL = 10 Ω
Figure 28. Turn-Off Response Time
C025_lvsb39.png
VIN = 1.5 V TA = 25°C CIN = 1 µF
CL = 0.1 µF RL = 10 Ω
Figure 30. Turn-Off Response Time