Pogo pins power clarification - reading schematics
03-14-2021, 11:30 AM
(This post was last modified: 03-14-2021, 11:32 AM by bokomaru.
Edit Reason: minor grammar
)
Thanks, everyone! Looks like the wiki gave this topic a little more visibility.
Lots of info in the last week, and I won't try to keep up with everything all at once.
@GregH, I'm glad you have a solution via the convergence dock! I don't have an opinion yet about renaming the pogo pins, but it's worth discussing. And by the way, thank you for rolling up your sleeves and physically trying some test cases and sharing with us.
@dsimic, it sounds like you and I are mostly in alignment now, e.g., about USB-5V not being an input. Definitely a long post, so maybe I will follow up later on some points there.
@scholbert, your picture does say more than 1000 words, confirmed :-) Building on @smaeul's comments, we could add in the ANX7688 to this picture too.
@smaeul, thanks for confirming/describing in your own words DCIN and USB-5V, and for adding new info and answers to this discussion to fill in some of the gaps. Earlier, I did just barely touch on the ANX7688's relevance here, but I didn't understand it this well.
I'll only attack one topic today in this post, and I think @smaeul just beat me to it :-P
I think I can show that the "other" voltage on USB-5V is neither due to a capacitor nor reverse current through U1302. (It really is battery voltage coming from PS across D600)
Phone powered on, no external power attached. Measure USB-5V to be ~ 3.9 V. Connect a 1 k ohm resistor (brown black red) between USB-5V and GND, to draw a few mA of current. Measure voltage at DCIN to be 0 V. Measure voltage at USB-5V to be ~ 3.7 V.
It's not "residual capacitance", because I'm drawing current, and the voltage is constant w/o decaying, even over minutes of time while drawing a few mA of current.
It's not "reverse current" through U1302, because the "reverse source" side of U1302 would be its VOUT, which is the Pinephone's DCIN, which I measured to be 0 V.
So I think that when the LP6226 is disabled, current really does just flow from PS through D600 to USB-5V. Even if that wasn't totally "intended", I don't see why it would be an issue for a pogo expansion board to draw current from USB-5V even while the LP6226 is disabled, since PS is still the source in either case.
Lots of info in the last week, and I won't try to keep up with everything all at once.
@GregH, I'm glad you have a solution via the convergence dock! I don't have an opinion yet about renaming the pogo pins, but it's worth discussing. And by the way, thank you for rolling up your sleeves and physically trying some test cases and sharing with us.
@dsimic, it sounds like you and I are mostly in alignment now, e.g., about USB-5V not being an input. Definitely a long post, so maybe I will follow up later on some points there.
@scholbert, your picture does say more than 1000 words, confirmed :-) Building on @smaeul's comments, we could add in the ANX7688 to this picture too.
@smaeul, thanks for confirming/describing in your own words DCIN and USB-5V, and for adding new info and answers to this discussion to fill in some of the gaps. Earlier, I did just barely touch on the ANX7688's relevance here, but I didn't understand it this well.
I'll only attack one topic today in this post, and I think @smaeul just beat me to it :-P
(03-14-2021, 07:42 AM)megous Wrote: - USB-5V seems like it should always be 5V if PS-5V is enabled and if it has some other voltage when PS-5V is disabled, it's only because there's some remaining charge on the capacitors, or some current going in the reverse direction via U1302 via internal N-MOSFET body diode (see https://megous.com/dl/tmp/06d11858b841c503.png - there's a parasitic diode between S-D in that direction) You're not supposed to rely on USB-5V in this case, when PS-5V is off (another diode on the PS-5V output prevents backfeeding of power through PS-5V)
I think I can show that the "other" voltage on USB-5V is neither due to a capacitor nor reverse current through U1302. (It really is battery voltage coming from PS across D600)
Phone powered on, no external power attached. Measure USB-5V to be ~ 3.9 V. Connect a 1 k ohm resistor (brown black red) between USB-5V and GND, to draw a few mA of current. Measure voltage at DCIN to be 0 V. Measure voltage at USB-5V to be ~ 3.7 V.
It's not "residual capacitance", because I'm drawing current, and the voltage is constant w/o decaying, even over minutes of time while drawing a few mA of current.
It's not "reverse current" through U1302, because the "reverse source" side of U1302 would be its VOUT, which is the Pinephone's DCIN, which I measured to be 0 V.
So I think that when the LP6226 is disabled, current really does just flow from PS through D600 to USB-5V. Even if that wasn't totally "intended", I don't see why it would be an issue for a pogo expansion board to draw current from USB-5V even while the LP6226 is disabled, since PS is still the source in either case.
