SLYY193C january   2023  – april 2023 LMQ61460-Q1 , TPS54319 , TPS62088 , TPS82671 , UCC12040 , UCC12050

 

  1.   At a glance
  2.   Authors
  3.   3
  4.   What is power density?
  5.   What limits power density?
  6.   What limits power density: switching losses
  7.   Key limiting factor No. 1: charge-related losses
  8.   Key limiting factor No. 2: reverse-recovery losses
  9.   Key limiting factor No. 3: turn-on and turn-off losses
  10.   What limits power density: thermal performance
  11.   How to break through power density barriers
  12.   Switching loss innovations
  13.   Package thermal innovations
  14.   Advanced circuit design innovations
  15.   Integration innovations
  16.   Conclusion
  17.   Additional resources

Key limiting factor No. 2: reverse-recovery losses

In a buck converter, reverse recovery occurs when the high-side MOSFET turns on while the body diode of the low-side MOSFET is conducting current, thus forcing the low-side diode current to rapidly transition to the high-side MOSFET. In the process of this transition, a current is required to remove the low-side diode minority charge causing a direct switching loss, see Equation 4.

Equation 4. E R R = V I N × I L × t R R + V I N × Q R R  

One of the best approaches to reduce the impact of diode reverse recovery is to reduce the stored charge (QRR) through optimized MOSFET design, or to reduce or eliminate the rising edge dead time, thus negating the impact of the loss completely.