SLVAFB4 July   2022 TPS62902-Q1 , TPS62903 , TPS62903-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Inverting Buck – Boost Topology
    1. 1.1 Concept
    2. 1.2 Output Current Calculations
    3. 1.3 VIN and VOUT Range
  4. 2Digital Pin Configurations
    1. 2.1 Enable Pin
    2. 2.2 MODE/S-CONF Pin
    3. 2.3 Power Good Pin
  5. 3Design Considerations
    1. 3.1 Input Capacitor Selection
    2. 3.2 Output Inductor Selection
    3. 3.3 Stability Limits and Output Capacitor Selection
  6. 4Typical Performance and Waveforms
  7. 5Conclusion
  8. 6References

1.3 VIN and VOUT Range

The input voltage that can be applied to an inverting buck - boost converter is less than the input voltage that can be applied to the same buck converter. This is because the ground pin of the IC is connected to the negative output voltage. Therefore, the input voltage across the device is VIN to -VOUT, not VIN to ground. Thus, the input voltage range of the TPS62903 is 3 V to 17 V+ VOUT, where VOUT is a negative value. The minimum input voltage stays the same at 3V because the device will not turn on during startup when the negative VOUT is not present.

The output voltage range is the same as when configured as a buck converter, but negative. The TPS62903 output voltage for the inverting buck - boost topology should be set between –0.6 V to –5.5 V for external divider and -0.4 V to -5.5V for internal divider (VSET). It can be set the same way as in the buck configuration, with two resistors connected to the FB pin or VSET configuration. Due to the increased noise of the inverting buck - boost topology, for a more robust design, recommend use internal feedback (VSET) or use smaller value resistors than are used for the buck configuration.