SLYT819 October   2021 BQ25980

 

  1. 1 Introduction
  2. 2 Delivering over 100 W power with USB PD
  3. 3 High-efficiency switched-capacitor DC/DC converters
  4. 4 Output impedance
  5. 5 Switching losses
    1. 5.1 Turnon switching loss
    2. 5.2 Turnoff switching loss
    3. 5.3 Gate driving loss
  6. 6 Dual-phase interleaved switched-capacitor converter
  7. 7 High-power-density switched-capacitor converter
  8. 8 Switched-capacitor converter application: fast charging for portable devices
  9. 9 Conclusion
  10. 10Related Websites
  11. 11Important Notice

5.1 Turnon switching loss

The fixed 50% duty cycle makes it possible to control the voltage across the flying capacitor and output voltage to close to half the input voltage. Until the switches are fully turned on, the current flowing through the device is very small and the switches can achieve close to zero current turn on. The IV overlap loss is almost eliminated during turn on.

The energy stored in the drain-to-source junction capacitance of the switches is lost during the turnon process, so there is junction capacitance loss, as shown in Equation 9:

Equation 9. P D S = 1 2 C D S V O U T 2 f s w

where, CDS is the drain-to-source junction capacitance, VOUT is the output voltage and fsw is the switching frequency.