On 03/06/2024 23:00, Jonathan Cameron wrote: > On Mon, 3 Jun 2024 12:46:10 +0300 > "Ceclan, Dumitru" <mitrutzceclan@xxxxxxxxx> wrote: > >> On 01/06/2024 21:35, Jonathan Cameron wrote: >>> On Fri, 31 May 2024 22:42:27 +0300 >>> Dumitru Ceclan via B4 Relay <devnull+dumitru.ceclan.analog.com@xxxxxxxxxx> wrote: >>> >>>> From: Dumitru Ceclan <dumitru.ceclan@xxxxxxxxxx> ... >>>> + Supported only by AD7172-2, AD7172-4, AD7175-2, AD7175-8, AD7177-2: >>>> + 19: ((AVDD1 − AVSS)/5)+ >>>> + 20: ((AVDD1 − AVSS)/5)− >>> >>> That's what it says on the datasheet (so fine to copy that here) but I'm curious, what does >>> that mean in practice? How can we have negative and postive signals of the difference >>> between two power supply voltages where I'm fairly sure AVDD1 always greater than AVSS. >>> >> >> I have not tested that as I do not have a model that supports this wired up. >> If I had to guess they are the same signal but one should be connected to the >> positive input, one to the negative input...but I could be wrong. > > If they are, then as far as I we are concerned is this one channel with two > representations depending on whether it is 1st or 2nd in the list? > Can we use one number and hide that detail in the driver? > > Seems odd though if that is the case. > > I guess if we find out later this is the case we can tighten the binding to > enforce the right one instead of squashing them to one value, but that > is a bit ugly. Any chance of digging out the info? If not we can go ahead > but ideally answering things like this make a our life easier in the long run. > > Jonathan > "(Avdd1/Avss)/5+ as positive input and (Avdd/Avss)/5- as negative this is used for monitoring power supplies, the inputs must be selected in pair" Perhaps it's an internal voltage divider...? I dunno So it seems like this cannot be used as a common mode voltage input. I'll restrict the driver to only allow these inputs paired together and rename the define for these selections.
