SLVAG21 April   2026 TPS61381-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2System Overview
    1.     6
    2. 2.1 Design Considerations
    3. 2.2 System Design Theory
      1. 2.2.1 Supercapacitor Charging Operation
        1. 2.2.1.1 Calculation for Backup Supercapacitor Selection
          1. 2.2.1.1.1 Design Calculations
  6. 3Test Results
    1. 3.1 Standby Operation
    2. 3.2 Charging Operation
    3. 3.3 Boost Operation
  7. 4Summary
  8. 5References

3.3 Boost Operation

Figure 3-3 shows the backup action of the system in play. If the mains supply fails, the TPS61381 converter immediately starts regulating the system voltage to the programmed output voltage. The supercapacitor is discharged and the voltage decreases slowly. When the backup capacitor voltage reaches the IC current limit or the minimum voltage of the TPS61381 (around 1V), the converter stops operating and the system voltage decreases to zero.

Backup Operation with Vbub=5.4V, Vout=12VFigure 3-3 Backup Operation with Vbub=5.4V, Vout=12V

In this scope plot, the backup time is approximately 200ms. Larger backup capacitor values result in a longer backup time, in accordance with the previous equation described in section 2.3.2.