Hey #electronics lazyweb #AskFedi, does anyone know what the WCH CH224 family does if you configure the sink to request 20V but the source can’t do that? Specifically I’d like to know how it responds to both a “dumb” 5V source, and a PD source that only goes up to 12V.
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@jpm I dunno what that chip does, but what's supposed to happen by spec is if there's no PD agreement, there's NO supply to Vbus. Not even +5V.
If the legacy mode resistors are present on the sink, then there's +5V on Vbus, but no PD negotiation.
There isn't any standard way to get higher than +5V (nominal) on Vbus without PD negotiation, though some vendor-proprietary crap (pre-PD) might do it.
@brouhaha and yeah that’s what I’m wondering about - does this chip only negotiate the set voltage, or does it negotiate up to that set voltage?
@jpm
If you use the resistor on CF1, just the fixed voltage. If you use logic levels on CF[1:3], or I2C, you can change it dynamically, but at any given time it only negotiates for what those config pins tell it.
There's no way to tell it, "negotiate the highest voltage you can."
You could program e.g. a CH32X035 to do what you want, but I don't know how much you'd have to hack, starting from an SDK example
@jpm it defaults to 5V output, but the “PG” LED doesn’t go off IIRC.
@jpm hold on I have a PD trigger USB analyser and a CH224 here, lemme do some science
@jpm ok so the CH224 overrides any PD triggers along the chain to get what it wants. If I chuck dumb 5V in, it will put 5V out but the PG LED pin will go silent. Unfortunately I don’t have a charger on me right now that does protocols other than the full 65W suite (ie 9/12*/15/20) so I can’t tell you much more than that for now.
@ThermiteBeGiants yep I figured dumb* 5V would end up with 5V because there’s always voltage on VBUS
(Ping @Unixbigot I suspect you’ve (ab)used CH224’s extensively)
@jpm hmmmn, i think I have some but i dont think i’ve used them yet. Lemme check.
@jpm Well, I didn't expect that.
5v only PD supply -> 5v
Non PD supply -> 5v
20v capable PD supply -> 20v
19v supply -> 19v
18v supply -> 18v
17v supply -> 17v
16v supply or lower -> crash loop
I tried another of my switchable PD decoy modules, and that one limits its max output to the highest of 5,9,12,15,20 that is higher than the PD supply
