SNVAA61 February   2023 LM5168 , LM5168-Q1 , LM5169 , LM5169-Q1

 

  1.   Inverting Buck-Boost Application for LM5168
  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
    2. 3.2 Inductor 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 = -12 V Typical Performance
    2. 5.2 VOUT = -24 V Typical Performance
    3. 5.3 VOUT = -48 V Typical Performance
  8. 6Conclusion
  9. 7References

2.1 Bypass Capacitor and Optional Schottky Diode

A new bypass capacitance, from VIN to -VOUT is used to help with load transients. The value for the bypass capacitance, CIO, can be chosen using input capacitance recommendations from the buck datasheet, but it is important to note that the voltage across the capacitors will be VIN + |-VOUT|. The capacitors used should be appropriately sized for the voltage difference between VIN and -VOUT. When the input supply is turned on, the bypass capacitance may cause the output to shortly swing positive before becoming negative. If the desired load is sensitive to a positive swing, then an optional Schottky diode can be placed across the output to clamp the voltage.

Figure 2-1 LM5168 Inverting Buck-Boost with Optional Schottky Diode