Other Parts Discussed in Thread: CSD18563Q5A, , TPS23756
Hello,
* I am using UCC24612-2 in flyback as Low-Side SR in 25W loading system, Vload = 5V.
* I found that when the flyback system with Low-Side SR working at CCM (power loading is around 23W) the SR MOSFET VDS has a high voltage spike which has exceed the rating of the MOSFET。Vgs proportional drive is 50%, Vds max spike is 75V
* The SR-MOSFET is CSD18563Q5A (Rds on ~12mOhm) ;
* Using eq 1 in UCC24612 datasheet, the secondary side peak current (I load) = 4.38A, the measured minimum Rds on of SR MOSFET is 23mOhm.
* I change SR-MOSFET with larger Rds on (PSMN059-150Y,115 ; Rds on = 50mOhm), but with this new MOS, there are no proportional gate drive, hence Vds spike is much higher compare to previous MOS (133V compare to 75V)。
my question is :
* Is my approach in dealing with Vds spike wrong? I could use snubber to dampen the spike, but i want to make sure that i use the proper MOSFET for the design
* Did I missed something important when designing the system?
* Is UCC24612-2 suitable for flyback low side SR CCM mode (25W loading)?
* CSD18563Q5A Vds, Vgs during CCM
* PSMN059 Vds. Vgs during CCM
thank you