SLVSDH0C December   2016  – January 2018 TPS22810

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Simplified Schematic
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin 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
    7. 7.7 Typical DC Characteristics
    8. 7.8 Typical AC Characteristics
  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 and Off Control
      2. 9.3.2 Quick Output Discharge (QOD)
        1. 9.3.2.1 QOD when System Power is Removed
        2. 9.3.2.2 Internal QOD Considerations
      3. 9.3.3 EN/UVLO
      4. 9.3.4 Adjustable Rise Time (CT)
      5. 9.3.5 Thermal Shutdown
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 ON and OFF Control
    3. 10.3 Input Capacitor (Optional)
    4. 10.4 Output Capacitor (Optional)
    5. 10.5 Typical Application
      1. 10.5.1 Design Requirements
      2. 10.5.2 Detailed Design Procedure
        1. 10.5.2.1 Shutdown Sequencing During Unexpected Power Loss
        2. 10.5.2.2 VIN to VOUT Voltage Drop
        3. 10.5.2.3 Inrush Current
      3. 10.5.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
    3. 12.3 Thermal Considerations
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Developmental Support
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.5.2.3 Inrush Current

To determine how much inrush current is caused by the CL capacitor, use Equation 9.

Equation 9. TPS22810 Q3_Iinhush_slvsco0.gif

where

  • IINRUSH is the amount of inrush caused by CL
  • CL is the capacitance on VOUT
  • dt is the Output Voltage rise time during the ramp up of VOUT when the device is enabled
  • dVOUT is the change in VOUT during the ramp up of VOUT when the device is enabled

The appropriate rise time can be calculated using the design requirements and the inrush current equation. As we calculate the rise time (measured from 10% to 90% of VOUT), we account for this in our dVOUT parameter (80% of VOUT = 9.6 V) as shown in Equation 10 and Equation 11.

Equation 10. 400 mA = 22 µF × 9.6 V/dt
Equation 11. dt = 528 µs

To ensure an inrush current of less than 400 mA, choose a CT value that yields a rise time of more than 528 μs. Consulting Table 2 at VIN = 12 V, CT = 4700 pF provides a typical rise time of 957 μs. Using this rise time and voltage into Equation 9, yields Equation 12 and Equation 13.

Equation 12. IInrush = 22 µF × 9.6 V/ 957 µs
Equation 13. Inrush = 220 mA

An appropriate CL value must be placed on VOUT such that the IMAX and IPLS specifications of the device are not violated.