SNVA856B May   2020  – October 2022 LM63615-Q1 , LM63625-Q1 , LM63635-Q1 , LMR33620 , LMR33620-Q1 , LMR33630 , LMR33630-Q1 , LMR33640 , LMR36006 , LMR36015 , TPS54360B , TPS54560B

 

  1.   Working With Inverting Buck-Boost Converters
  2.   Trademarks
  3. 1 Introduction
  4. 2 Inverting Buck-Boost Converter
  5. 3 Basic Operation
  6. 4 Operating Considerations of a Buck Based Inverting Buck-Boost
    1. 4.1 Voltage Stress
    2. 4.2 Current Stress
    3. 4.3 Power Loss and Efficiency
    4. 4.4 Small Signal Behavior
      1. 4.4.1 Measuring IBB Bode Plots
      2. 4.4.2 Testing Load Transients on an IBB
      3. 4.4.3 Simulation
  7. 5 Component Selection for the IBB
    1. 5.1 Inductor Selection
    2. 5.2 Capacitor Selection
    3. 5.3 External Feed-back Divider
  8. 6 General Considerations
  9. 7 Auxiliary Functions
    1. 7.1 Enable Input Level Shift
    2. 7.2 Synchronizing Input Level Shift
    3. 7.3 Power-Good Flag Level Shift
    4. 7.4 Output Clamp
    5. 7.5 Output Noise Filtering
  10. 8 Design Examples
    1. 8.1 Converting +12 V to –5 V at 3 A
    2. 8.2 Converting +5 V to –5 V at 1 A
  11. 9 Summary
  12. 10References
  13. 11Revision History

4.4.1 Measuring IBB Bode Plots

Since the ground of the buck regulator is floating on the negative output, taking a Bode plot for the IBB needs some consideration. The setup shown in Figure 4-2 has proven helpful when taking this measurement in our lab. Note that the grounds of the input probes to the frequency response analyzer need to be floating with respect to the input power supply and load ground (system ground), while the injection transformer used with the analyzer, isolates the source. The probe grounds (common) are connected to the negative output as shown in Figure 4-2 . These connections must form a star point as close as possible to the bottom terminal of RFBB. The value of RINJ is usually between 10 Ω and 50 Ω.

GUID-30C60EB6-ADAE-487A-AB8C-1BF5BA247202-low.gifFigure 4-2 Set-up for Measuring Bode Plots for an IBB