Exactly. We would need very precise measurements and tightly controlled test conditions if we were actually out to prove that one is better than the other. But to prove that the info from the datasheet applies in the way we thought it would? No problem, you and Tom E have already done that, in spades!
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.