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

4.1 Frequency Setting

Many factors influence frequency selection. Higher switching frequency leads to smaller output inductor and capacitors, reducing the size of the converter. However, higher switching frequencies increase switching losses, and lower the efficiency of the converter. A frequency of 300 kHz is chosen for this design for reasonable efficiency and size.

Capacitor C16, which is connected from CT (pin 5) to ground, programs the oscillator frequency. A C16 value of 47 pF yields a switching frequency of 300 kHz at 25°C.