HATs and other add-ons • Re: Power Hat+ spec questions

Is there a way to make a power hat that uses GPIOs and signals that it is not compatible with a Standard hat?

Yes, the answer is right there in the spec:

Standard
Any HAT+ that uses the typical HAT+ pins also used by legacy HATs, including HAT+s that also provide power.

If you have a HAT that uses GPIOs and provides power, then it is a Standard HAT. The spec says that you can only connect one HAT from each class together at the same time, so by virtue of being a Standard HAT itself, it is thus incompatible with other Standard HATs.

However, it does raise a question about whether one can still use the accoutrements of the Power class with a Standard HAT - that is, when identifying as a Power HAT, that will tell the Pi that it provides power, and when the EEPROM specifies a DT overlay, how much current it can provide. I think it may be possible to use with a Standard HAT the DT overlay as suggested in section 4.2 of the spec, with the exception that the Mode 0/1 overrides won't work.

If a power hat uses GPIOs it would not be Hat+ spec compliant but could still work?

Indeed, such a Power HAT would not be HAT+ compliant. But as above, a Standard one would.

For power mode1 does anyone have an updated ideal diode schematic/parts list that would support 5Amps? The mosfet (DMG2305UX) used in the sample from the original hat spec https://github.com/raspberrypi/hats/blo ... ircuit.png supports 4.2A.

There are plenty of P-channel MOSFETs out there that support higher current. Just make sure it has adequately-low RDS(on) at VGS of around -4V, and also a VGS(th) that actually turns it on fully at that voltage. I would recommend using something larger than a SOT-23 if you expect to support continuous loads of 5A - something like a SO-8.

Here's a MOSFET I've used in similar application: AO4409. At 5A it only dissipates 0.3W and will only get to a temperature of around 48C (at 25C ambient). There are also several '4409' clones available from other manufacturers (but note, not Vishay Si4409 - that is something with very different specs and not suitable).

Statistics: Posted by HwAoRrDk — Tue Dec 10, 2024 2:12 pm

---