200V, 17A N-Channel — what the drain rating means on your rail
The IRFR15N20DTRPBF: That 200 V Vdss gives you a solid margin on a 48 V or 72 V bus, and it will handle the peak voltage on a 120 V DC link in a motor drive without derating anxiety.
165 mOhm on-resistance — sizing the conduction loss
Maximum Rds(on) is 165 mOhm with 10 V gate drive at 10 A drain current. At 10 A the conduction loss is 16.5 W — that number drives the heatsink decision.
