17mm & 20/26/27mm single-sided DD/FET driver release: A17DD-SO8 / A20DD-SO8 / etc

[wight]

@wight

[snip] All that said, anyone wants to play around with testing different FETs, here are 3 which all appear to have some superior characteristics:

• PSMN0R9-30YLD - rufusbduck pointed this one out, it has very similar characteristics to PSMN3R0-30YLD but is better. Slightly lower Rds(on) and slightly lower Vgs. Also significantly higher “total power dissipation”. We expect the lower Vgs to ensure that the FET remains more “fully open” on single cell setups.
• SiR800DP - comfychair pointed this one out to me in reference to this driver by PM weeks ago. I forgot about it until I went looking for FETs which I thought might work properly with the QX7136-based A17LDQX driver and it turned up again in that context. Much lower Rds(on) than our selections so far and even lower Vgs than RBD’s selection. Again, the low Vgs should help keep the FET fully turned on.
• SiS414DN - Another one which turned up during my search for good FETs for the QX7136. Low maximum current handling, 20A “package limited”. I’m not really sure exactly what a package limit involves, since we know that PowerPAK® SO-8 can handle at least 50A (the SiR800DP is spec’ed for that) and the graph in the datasheet goes way beyond 20A. Even lower Rds(on) than SiR800DP, but only slightly. Similar Vgs characteristics to SiR800DP. Lower Qg than SiR800DP, but I doubt that that will help us any. Costs less than the other two FETs in this list.

@wight

[snip]

@Rufusbduck

Typically we look at Rds on as tied to gate voltage but after slogging through some of these data sheets I see that it also varies with drain current and temp just not as dramatically. Which makes sense since resistance in most things goes up with temp. To test more would you start with the third possibility in the hope of seeing gains at lower cost in spite of the current limit or with CC’s suggestion to find the possible upper limit?

[snip] I wouldn’t have listed all 3 if I didn’t think that they were all just as worthwhile to test. That said, the maximum gain anyone can expect to see for an XP-G2 is probably around 0.1A, maybe 0.15A - and it doesn’t matter what FET package we are talking about, we’re that close to true DD here. The higher the current, the higher the gains, but there’s still very little to be had!

So errr, don’t order SiS414DN to use on this driver. I must have missed the fact that it’s actually PowerPAK 1212-8, a much smaller package than LFPAK56. That’s why the “package limited” values seemed so low!

Now I’m stuck w/ two of them (which I ordered for testing with the QX7136 over here)… maybe that’s an excuse to make a smaller driver of some type?