Pogo pins power clarification - reading schematics

[bokomaru]

Here comes lots more quotes and replies!

I made some measurements myself... though i try prevent a complete disassembly right now.

I'm trying to avoid disassembling too. No worries :-)

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)

Confirmed.

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?

I'm starting to think this is true. It explains why we see the battery voltage when the PMIC doesn't have an ACIN/VBUS input, and why I see a higher voltage at DCIN when ACIN/VBUS is present.

There's one thing it doesn't explain. See (3) below.

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)

Measurement confirmed, but I'm not convinced about the conclusion. I hope the schematics are accurate!

Going by schematics, it's true that the same DCIN net doesn't actually go _all_ the way to the USB C connector. On the USB-C small board, there's one component U102, which is an AW338XX "load switch", which is I guess supposed to break the connection if there's too much current or voltage. Maybe the AW338XX doesn't behave like a zero resistance wire for whatever signal our multimeters use for checking connectivity?

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.

Confirmed.

I broke out a female/host USB A connector to play the part of a "power brick". Just the VCC pin and GND. Hooked it up to a variable power supply.

Made at least 20 voltage measurements.

Let "Vs" be the "supply voltage" output setting on the variable power supply. Let Vb be the "battery voltage" that you'd measure directly across the +/- terminals on the removed battery. Now, for Vb ~= 4.08 V, and Vs = 4.70 V, 4.80 V, 4.90 V, 5.00 V, 5.10 V, 5.20 V, or 5.30 V:

Phone off:

Code:

PIN5 = Vs - 0.20 V
PIN1 = Vs - 0.35 V

Phone on:

Code:

PIN5 = Vs - 0.20 V
PIN1 = Vb

Example:

Code:

When Vs = 5.00 V,
PIN5 = 5.00 V - 0.20 V = 4.80 V

It's just a rough formula to describe that pattern I saw. Actual deviation from this was just a few hundredths of a volt though. All the time, the variable supply indicated it was hitting its target voltage (not sagging or something). The phone pulled around 450 mA off, or if the phone was on and doing something, closer to the 1 A limit that I configured.

Next, I tried with three different USB "brick" AC to DC supplies, including one that's a fancy wall outlet with a built-in USB port:

Code:

PIN5    PIN1

old ipod brick, labeled 500 mA
4.3 V   4.1 V     (phone on)
4.4 V   4.3 V     (phone off)

fancy wall outlet, unknown characteristics
4.8 V   4.7 V     (phone on)
4.9 V   4.7 V     (phone off)

newer generic brick labeled 1 A
5.0 V   4.8 V     (phone on)
5.1 V   4.9 V     (phone off)

And we still know that without a power supply, we have:

Code:

PIN5 = 0.0 V
PIN1 = Vb

Some things to notice:

1. If a "charging brick" is connected to the USB C port, the voltages at both PIN5 and PIN1 seem to be directly determined by the voltage of the USB C port supply.
   
2. If a "charging brick" is not connected to the USB C port, the voltage at PIN1 is the battery voltage.
   
3. If the phone is powered on, my "hacked together" variable supply (fake "brick") doesn't affect PIN1's voltage. PIN1 remains at the battery's voltage.
   

On (3): That's pretty strange, no? There must be something else I need to do to convince the phone that I'm a charger. But this also makes me see it your way, doubting if PIN1/DCIN is connected to the USB C port like the schematics say.

In any case, it's pretty clear to me that the wiki's statement "the second power pin is VBAT, which connects to the battery voltage" is inaccurate, or at best is an incomplete description of PIN1.

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

Unfortunately, an actual battery is actually necessary for the short bursts of high current draw from the modem, apparently on the order of Amps. So your solution to that problem would work to power part of the system, but not all. Properly powering an isolated mainboard requires a battery-like device, plus another power source for powering the phone + charging the battery. I don't see a way around it.

Only written words so far, so maybe in the end they found out that the Pogo Pins could not be used for that.

Maybe, but I hope not true! The blog says these have gone into production already. You'd think it works.

If they connect the "real" Qi-Charger to Pin5 (wiki name VBUS), then this would be the pin to power the boards... obviously

Ahaha, too bad that's the opposite conclusion of how I read the schematics. I feel like we still have no idea which pin would be the charging input or why.

We've definitely made some progress though :-)