Pogo pins power clarification - reading schematics

[megous]

I'll only attack one topic today in this post, and I think @smaeul just beat me to it :-P

- 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.

Right, I didn't notice the inductor.