SNVAA65 March   2023 LM63610-Q1 , LM63615-Q1 , LM63625-Q1 , LM63635-Q1

 

  1.   Abstract
  2.   Trademarks
  3. 1Inverting Buck-Boost Topology
    1. 1.1 Concept
    2. 1.2 Output Current Calculations
    3. 1.3 Voltage Range of Inverting Buck-Boost Configuration
  4. 2Design Considerations
    1. 2.1 Bypass Capacitor and Optional Schottky Diode
  5. 3External Components
    1. 3.1 Capacitor Selection
  6. 4Digital Pin Configurations
    1. 4.1 Optional Enable (EN) Level Shifter
    2. 4.2 Power-Good (PG) Pin
  7. 5Typical Performance
    1. 5.1 VOUT = -3.3 V, 2.1 MHz Typical Performance
    2. 5.2 VOUT = -3.3 V, 400 kHz Typical Performance
    3. 5.3 VOUT = -5 V, 2.1 MHz Typical Performance
    4. 5.4 VOUT = -5 V, 400 kHz Typical Performance
  8. 6Conclusion
  9. 7References

1.3 Voltage Range of Inverting Buck-Boost Configuration

When using a buck converter as an inverting buck-boost, the connection changes limit the voltage range from input to output that the part can safely operate at. The ground (GND) pin of the IC is no longer referenced to 0 V, and it is now the output of the converter. As a result, the maximum voltage over the IC can be calculated as VIN minus -VOUT. For example, if the input voltage is 24 V and the output is -24 V, then the voltage over the IC is 48 V. In the case of the LM63615-Q1, this configuration would exceed the maximum input voltage of 36 V across the part listed in the data sheet. It is important to keep the input and output voltage difference within the maximum voltage rating of the IC.