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

3.2.2.2 Output Ripple Voltage

The output capacitor must supply the current when the high-side switch is off. Use the minimum input voltage to calculate the output capacitance needed. This is when the duty cycle and the peak-to-peak current in the output capacitor are the maximum. Using the 1% voltage ripple specification and Equation 9, COUTmin is 15 μF. Use Equation 10 to calculate the maximum ESR an output capacitor can have to meet the output-voltage ripple specification. Equation 10 indicates the ESR should be less than 20.8 mΩ. In this case, the ESR of the ceramic capacitor is much smaller than 20.8 mΩ.

Equation 9. GUID-24D809B6-3094-40F9-B86C-B936C69EFBEA-low.gif
Equation 10. GUID-422269F1-F700-4E5B-BAA9-E7A01D9D61BF-low.gif

An output capacitor that can support the inductor ripple current must be specified. Some capacitor data sheets specify the RMS value of the maximum ripple current. Use Equation 11 to calculate the RMS ripple current that the output capacitor must support. For this application, Equation 11 yields 2.08 A for the output capacitor.

Equation 11. GUID-95D40072-0620-404B-AD79-112FA2B4DE32-low.gif