I want to replace a MOSFET in a legacy product. The MOSFET is a P-channel Power MOSFET that is used for PWM switching purposes (VGS @ -12V, PWM is 20% @ 200us). The FET is switching in to a 200uH, 10ohm load (see image, 5 and 6 are a coil of 5ohms 200uH @ 10KHz). The FET has quite a large heatsink attached due to it getting hot. I'm wondering if the RDS(on) of 1.5 ohms may be the culprit as this is fairly high resistance in saturation mode? Would it be worth looking at alternatives with similar characteristics but with lower RDS(on) (in the milli-ohm range)? Or is the issue potentially more complicated / caused by the load? Any help would be great.
Lower RDson often means higher gate charge/capacitance which slows down switching and increases switches losses. Things could get hotter depending on the balance between conduction and switching losses. So pay attention to both total gate charge and RDson when choosing.