Pogo pins power clarification - reading schematics

[scholbert]

Some investigation with a multimeter:

With a powered down PinePhone, I get 0 V from PIN5 and 4.0 V (battery voltage, unloaded) from PIN1.

Power up the PinePhone with no charger in the USB C port. I get 0 V from PIN5 and 3.9 V (battery voltage, loaded, modem is off) from PIN1.

PinePhone still powered on, now I plug in a USB C charger. I get 5.0 V from PIN5 and 4.8 V from PIN1.

As I understand it, 4.8 V is the voltage of my external AC to DC power brick in the wall under whatever load. I don't _think_ that's the voltage at which the battery gets charged. I think the max allowed for charging a Li battery is around 4.2 or 4.3 V, and anyways, since this battery is almost full, it's probably in the constant-voltage phase of charging. Maybe I'll hook up to a variable power supply to investigate more.

What I'm hearing is that if you're powering an expansion board from the PinePhone's pogo pins, you can pick between a 5 V source or the battery voltage. But what I'm measuring is that if you pick PIN5, you get 0 V or 5 V depending on whether or not USB-5V is enabled. If you pick PIN1, you get either the battery voltage or the USB C connector's voltage, depending on whether or not an external power source is plugged in.

USB-5V and DCIN should be used to power your extension board... so, yes they should be seen as outputs.

Without a charger connected to USB Type-C DCIN is normally not present

I noticed something else. Without the charger plugged in to the USB Type-C port. So if you use PIN1/DCIN as an output from the PinePhone. Power is going from the battery into the PMIC, and then out of the PMIC's ACIN and VBUS pins? The AXP803 data sheet says ACIN and VBUS are type "PI" (I think Power Input). Is that drawing power "backwards" through the PMIC?

So to not confuse people with long post and "Quotes" i decided to split up the relevant parts... as you already did

To make it short...
I'm in doubt that the schematic gives us the correct information... and the comments i gave in my last post were based on these.
I made some measurements myself... though i try prevent a complete disassembly right now.

Checked the following connections:
USB Type-C cable connection (DCIN) to Pogo-Pins 5/1 (wiki names VBUS/VBAT) -> no direct connection -> conclusion: the schematic is wrong at this point no DCIN at Pogo Pin1 (T902)

Battery Connector VBAT (J600, Pin4) to Pogo-Pins 5/1 (wiki names VBUS/VBAT) -> no direct connection -> conclusion: no direct connection to the battery at VBAT Pogo Pin1 (T902)

To finalize here:
Pogo Pin1 (wiki name VBAT) reflects the Battery Voltage (on my device: Battery Voltage - 0.1V, as i did a direct measurement on the battery and then at the pin it to compare). I realize a short ramp up to 4.8V but then drops back to 3.9V.
It is not clear to which exact net this pin is connected. It's definetely not DCIN... nor is it VBAT (to be clear here: net names taken from the schematic).

Pogo Pin5 (wiki name VBUS) reflects the Power Supply Voltage. If it's plugged, i measure 5V, if not connected -> 0V.
Not sure about the schematic net entry about USB-5V here... i'm in doubt again that this is correct.

Imagine a scenario: Powering a lone mainboard. There would be no USB-C smallboard attached via the 40-pin connector. Would it now be safe to connect a 5 V source to pogo PIN1?

Another scenario: this "wireless coil design used in the back case" from the december blog update. The may blog update even says "Wireless charging coming to the PinePhone via add-on / using pogo pins". My guess was the wireless charger provides 5 V to PIN1/DCIN.

Yes i understand your aim...
Powering a standalone board:
As long as we don't know the exact electric path of Pogo Pin1, i would say some caution should be taken here.
We need to measure some of the nodes on the mainboard in relation to Pin1 to make things clear (reverse engineering is required).

If i should power the single board, i would design a 4.0V Power supply and attach it to the battery pins!

Wireless Charger backcase:
O.K. agreed... they wrote it on their blog... they showed us an evaluation board of a Qi-Charger... i never seen a real implementation working.
Only written words so far, so maybe in the end they found out that the Pogo Pins could not be used for that.

If they connect the "real" Qi-Charger to Pin5 (wiki name VBUS), then this would be the pin to power the boards... obviously
Again, we need to measure some of the nodes in relation to Pin5 to get things clear (reverse engineering again).

As you see i won't give a final advice here... as your mainboard may get damaged, if you try without knowing.
Right now i won't diassemble my Pinephone again, to help you with measurements... i'm sorry!

Hope this helps though!
Best regards,
scholbert