SLUU182A January   2004  – March 2022 TPS5124

 

  1.   Trademarks
  2. 1Introduction
  3. 2Features
  4. 3Schematic
  5. 4Design Procedure
    1. 4.1 Frequency Setting
    2. 4.2 Inductance Value
    3. 4.3 Output Capacitors
    4. 4.4 Input Capacitors
      1. 4.4.1 Case One: D1, D2 < 0.5
      2. 4.4.2 Case Two: D2 < 0.5 < D1
    5. 4.5 Compensation Design
    6. 4.6 Current Limiting
    7. 4.7 Timer Latch
      1. 4.7.1 Undervoltage Protection
      2. 4.7.2 Short Circuit Protection
      3. 4.7.3 Overvoltage Protection
      4. 4.7.4 Disabling the Protection Function
        1. 4.7.4.1 Disabling the Overcurrent Protection
        2. 4.7.4.2 Disabling the Overvoltage Protection or Undervoltage Protection
  6. 5Test Results
    1. 5.1 Efficiency Curves
    2. 5.2 Typical Operating Waveform
    3. 5.3 Start-Up Waveform
    4. 5.4 Output Ripple Voltage and Load Transient
  7. 6Layout Guidelines
    1. 6.1 Low-Side MOSFET
    2. 6.2 Connections
    3. 6.3 Bypass Capacitor
    4. 6.4 Bootstrap Capacitor
    5. 6.5 Output Voltage
  8. 7PCB Layout
  9. 8List of Materials
  10. 9Revision History

4.3 Output Capacitors

The required output capacitance and its ESR can be calculated using Equation 2 and Equation 3.

Equation 2. C O U T m i n =   I R I P P L E 8   × f   ×   V R I P P L E
Equation 3. E S R O U T =   V R I P P L E I R I P P L E

With 1% output voltage ripple, the required minimum output capacitance is 54 μF and its ESR should be less than 7.7 mΩ.

From the load transient point of view, the capacitance needed for 6% overshoot can be calculated using Equation 4.

Equation 4. C O U T =   ( I O U T ( m a x ) ) 2   × L ( V O U T 2 ) 2 -   ( V O U T 1 ) 2

where

  • VOUT2 is the allowed overshoot voltage.
  • VOUT1 is the nominal operating voltage.

For 6% overshoot, the required capacitance is about 370 μF. Four 100-μF, 6.3-V ceramic capacitors are used. Their ESR value is 2.0 mΩ each.