SNVAA71 October   2023 TPSM63610

 

  1.   1
  2.   Using the TPSM63610/08 for Negative Output, Inverting Buck Boost Application
  3.   Trademarks
  4. 1Inverting Buck-Boost Topology
    1. 1.1 Concept
    2. 1.2 VIN and VOUT Range In Inverting Configuration
    3. 1.3 Output Current Calculations
  5. 2Design Considerations
    1. 2.1 Additional Bypass Capacitor and Schottky Diode
    2. 2.2 Start-up Behavior and Switching Node Consideration
  6. 3External Components
    1. 3.1 Capacitor Selection
    2. 3.2 System Loop Stability
    3. 3.3 UVLO
  7. 4Typical Performance
  8. 5Digital Pin Configurations
    1. 5.1 Digital Input Pin (EN)
    2. 5.2 Power-Good Pin
  9. 6Summary
  10. 7References

1.3 Output Current Calculations

By changing the buck configuration into an IBB configuration, the average inductor current is affected. The output current capability in the IBB topology is less than the buck configuration. The maximum achievable current is calculated by the following:

Equation 1. IOUT (IBB) = IL_max × (1 – D)
  • IL_max is the maximum rated inductor current
  • D is the operating duty cycle

The operating duty cycle for an inverting buck-boost converter can be found with Equation 2.

Equation 2. GUID-FA986EE1-C06D-41BD-BEF2-569563F70EAF-low.gif
Note:

VOUT in Equation 2 is represented with a negative value.

The efficiency term in Equation 2 adjusts the equations in this section for power conversion losses and yields a more accurate maximum output current result. A conservative value efficiency of 70% is used for calculating the duty cycle. Use Equation 1 and Equation 2 to calculate the recommended maximum output current. For example a 24-V input voltage, –5-V output voltage application using the TPSM63610 power module results in a maximum output current of 6.2 A.

Table 1-1 Maximum Output Current Calculation for TPSM63610
VOUT (V) VIN (V) IL_max D IOUT (A)
-1.2 24 8 0.063 7.5
-1.8 24 8 0.093 7.3
-2.5 24 8 0.126 7.0
-3.3 24 8 0.161 6.7
-5 24 8 0.230 6.2
GUID-20230818-SS0I-GXHK-FJKB-TWP3B39WGGZK-low.svg Figure 1-2 Recommended Maximum Output Current for TPSM63610
Table 1-2 Maximum Output Current Calculation for TPSM63608
VOUT (V) VIN (V) IL_max D IOUT (A)
-1.2 24 6 0.063 5.6
-1.8 24 6 0.093 5.4
-2.5 24 6 0.126 5.2
-3.3 24 6 0.161 5.0
-5 24 6 0.230 4.6
GUID-20230818-SS0I-MSQM-70PC-H1ZK25KM5WTP-low.svg Figure 1-3 Recommended Maximum Output Current for TPSM63608