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

4.4.2 Case Two: D2 < 0.5 < D1

The ripple current through the input capacitor is shown in Section 4.4 and can be calculated using Equation 8.

Equation 8. 1 T   ×   ∫ 0 T 2   ( I O U T 1 -   I A V G ) 2 d t +   ∫ T 2 D 1   × T ( I O U T 1 +   I O U T 2 -   I A V G ) 2 d t +   ∫ D 1   ×   T T 2 + D 2   × T ( I O U T 2 -   I A V G ) 2 d t +   ∫ T 2 + D 2   × T T ( I A V G ) 2 d t
Equation 9. I i n c a p R M S =   D 1   ×   ( I O U T 1 ) 2 + D 2   × ( I O U T 2 ) 2 + 2   × D 1 - 1 ×   I O U T 1   ×   I O U T 2 -   ( I A V G ) 2  

This EVM meets “Case One” criteria. The maximum input ripple current is 6.7 A at VIN = 12 V. Two 150-μF, 20-V special polymer capacitors from Panasonic (part number is EEFWA1D151P) are used. It can handle 3.7 A of ripple current each. The ESR value of each capacitor is 26 mΩ. So the input ripple voltage is calculated using Equation 10 and is approximately 88 mVRMS.

Equation 10. IRIPPLE = IincapRMS × ESR