SLVA514C July   2014  – November 2022 TPS62125

 

  1.   Using the TPS62125 in an Inverting Buck-Boost Topology
  2.   Trademarks
  3. 1Inverting Buck-Boost Topology
    1. 1.1 Design Considerations
    2. 1.2 Concept
    3. 1.3 Output Current Calculations
    4. 1.4 VIN and VOUT Range
  4. 2Digital Pin Configurations
    1. 2.1 Enable Pin
    2. 2.2 Enable Hysteresis Pin
    3. 2.3 Power Good Pin
    4. 2.4 Discharging the Output Voltage
  5. 3Startup Behavior and Switching Node Consideration
  6. 4External Component Selection
    1. 4.1 Inductor Selection
    2. 4.2 Input Capacitor Selection
    3. 4.3 Selecting L and COUT for Stability
  7. 5Typical Performance and Waveforms
  8. 6Conclusion
  9. 7References
  10. 8Revision History

2.2 Enable Hysteresis Pin

The enable comparator typically has a built-in hysteresis of 50 mV. This hysteresis can be increased with an external resistor divider connected to the EN_hys pin. The equations to calculate the external resistor values for a buck converter are located in the applications section of the data sheet (Equations 6–10). Because the device is now an inverting buck-boost converter, the equations must be modified to account for VOUT, which is the GND terminal of the device. The VEN_TH_ON variable remains the same since there is usually no negative output voltage when the part is enabled. The equations for the inverting buck-boost topology are:

Equation 4. GUID-E2AF5F9A-8766-4625-A546-B2411581AE00-low.gif
Equation 5. GUID-7D5AA7C9-4A73-4418-AB80-C5A146762BC5-low.gif

In order for the VIN_stop threshold to operate, VIN_startup must be greater than VIN_stop - VOUT, where VOUT is a negative value.

If the EN_hys pin is not being used to adjust the hysteresis, it can instead be used to provide an output discharge path (explained in Section 2.4).