SLUU180B January   2022  – February 2022 TPS40070 , TPS40071

 

  1.   Trademarks
  2. 1Introduction
  3. 2Description
  4. 3Schematic
    1. 3.1 Output Filter Components
    2. 3.2 MOSFET Selection
    3. 3.3 Frequency Feedforward Resistor Selection
    4. 3.4 Output Voltage Setpoint
    5. 3.5 Short Circuit Protection Resistor Selection
    6. 3.6 Miscellaneous Parts
    7. 3.7 Control Loop Compensation
  5. 4Test Setup
  6. 5Results
    1. 5.1 Control Loop Characteristics
  7. 6Assembly Drawing and PCB Layout
  8. 7List of Materials
  9. 8Reference
  10. 9Revision History

3.5 Short Circuit Protection Resistor Selection

The current limit resistor, R9, is selected using Equation 5:

Equation 5. RLIM= ILIM × RDS(on)- VILIM(offset)ISNK

where

  • ILIM = IOUT (maximum) × 1.3
  • RDS(on) = 0.0085 Ω × 1.3 (for temperature correction)
  • VLIM(offset) = −0.030 V
  • ISNK = 80 mA

Using these conditions leads to selection of R9 = 1.4 kΩ. The capacitor C7 is chosen to be 10 pF to program a brief blanking interval.