SLVAFH1A December   2022  – December 2023 TPS62933 , TPS62933F , TPS62933O , TPS62933P

 

  1.   1
  2.   Create an Inverting Power Supply Using a TPS6293x Buck Converter With Internal Compensation
  3.   Trademarks
  4. 1Configuring the Buck Converter for Inverting Buck-Boost Topology Application
  5. 2Choosing the Correct Buck Converter for Inverting Power Application
    1. 2.1 Output Voltage Range
    2. 2.2 Input Voltage Range
    3. 2.3 Output Current Range
  6. 3Selecting Applicable External Components for Inverting Power Application
    1. 3.1 Resistor Divider
    2. 3.2 Inductor and Output Capacitor Selection
      1. 3.2.1 Inductor Selection
        1. 3.2.1.1 Output Current
        2. 3.2.1.2 Inductor Current Ripple
      2. 3.2.2 Output Capacitor Selection
        1. 3.2.2.1 Large Load Transient
        2. 3.2.2.2 Output Ripple Voltage
    3. 3.3 Input Capacitors
    4. 3.4 Bypass Capacitor
    5. 3.5 Enabling and Adjusting UVLO
  7. 4Experimental Results
  8. 5Summary
  9. 6References
  10. 7Revision History

3.2.2.1 Large Load Transient

The desired response to a large change in the load current is the first criterion. The output capacitor must supply the load with current when the converter cannot. Usually the converter requires two or more switching periods for the control loop to notice the change in load current and output voltage, and to adjust the duty cycle to react to the change. The output capacitor must be sized to supply the extra current to the load until the control loop responds to the load change, during which the capacitor voltage droops at the same time. Use Equation 8 to calculate the minimum required output capacitance.

Equation 8. C O U T ≥ ∆ I O U T × 3 T s ∆ V d r o o p

Where ΔIOUT is the change of output current, Ts is the switching period of the converter, and ΔVdroop is the allowable change in the output voltage.

For this example, ΔIOUT = 50% × IOUT = 0.6 A, Ts = 1/fs, and ΔVdroop = 2.5% × VOUT = 0.3 V, so you need at least 12 µF for the large load transient condition.