wvmarle:
I'm using the PMV16XN MOSFETs with 3.3V signals.
Vgs(th) = 0.65V, Rds(on) at Vgs = 2.5V and 6 A = 18 mOhm. USD 0.48 a piece on Mouser.
The FDD8447 is much more expensive at $0.85 (but can do 21A instead of a mere 8.6A for the PMV16XN, and it's big brother FDD8447L_F085 even 54A).
I only read this quickly and thought you said $1.85 for FDD8447, but what you actually said was 85c and compared that to 48c with the conclusion the FDD8447 is "much more expensive". Really? Seriously? This is likely a one off project and you would quibble about an extra 37c for a single part, for the only part in a solution?
I think perhaps a little perspective is required here. It is 37c! And who cares that it can carry half a country in current if it does the job and only costs 37c more than another part which is a nightmare to solder in.
MOSFETs are rarely used anywhere near their current rating. The RdsON factor is typically a far more significant parameter than any other in switching applications. That I mentioned the FDD8447 at all is something I am now regretting as everybody seems to have latched onto it whereas I only intended it as a reference to calculate switching times etc. Just for ball park numbers, not as an example of the perfect mosfet for the job, just one that is capable of doing the job (when I thought it was a 5V drive). Still, at 3V3 it aint no slouch and should cover the requirements comfortably. Not my ideal choice though; there are a few things I like not so much with this fet and this circuit.