There are a couple of FETs for the VDD1 linear regulator suggested by TI in the datasheet and E2E forums, BUK9213-30A and FDD8778, both of which are now obsolete. I'm looking for a replacement in the same D-PAK TO-252 package so that I don't need to spin the PCB. The tps65381 datasheet provides some guidance in section 4.5:
POS PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
AN Vgs(th) Gate threshold voltage, external FET ID = 1 mA 0.3 3 V
AN Ciss Gate capacitance, external FET VGS = 0 V 3 200 pF
AN Qgate Gate Charge, external FET VGS = 0 V to 10 V 70 nC
AN gfs Forward transconductance, external FET ID = 50 mA 0.4 S
There seems to be an abundance of FETs with gate characteristics that meet these criteria but I'm struggling a bit with the transconductance. For this application the FET will be operating continuously in the linear region dropping the 6V intermediate rail to the 1.2V required by the MCU core and in my application drawing around 200 mA. I get the impression that the datasheets for most MOSFETs are targeted to the SMPS market and focus on pulsed operation and RDS(on) which I don't think applies to this application. The datasheets that do mention transconductance provide specs while operating at double digit amps ranges, much more than the 50 mA condition speced for the TPS65381. Can you recommend a suitable replacement for the obsolete parts that have been used in this application previously?
