Pogo pins power clarification - reading schematics
01-09-2021, 02:25 PM
Well, I took it apart.
After this, my plan is to reassemble the phone and try applying power to pogo pins to confirm. If somebody wants me to test something while I have the mainboard in pieces, speak up now :-)
There are 3 test points at J1300. A pair of them are the USB DP and DM pins. Convert the PinePhone's USB C connector to a USB A port. The USB A's middle two pins, the data lines, have connectivity with these two test points.
The remaining test point T3 at J1300 is DCIN. It doesn't have connectivity with the USB C port because of U102. This test point has connectivity with the bottom-left pogo pin.
Now, ya have to unplug all the connectors and take the mainboard out of the phone case. And you have to remove the big metal shield covering everything up on the back.
You need the "PinePhone mainboard bottom placement v1.1" drawing to identify two capacitors C646 and C645. Once you realize how large they are, and where they are in relation to the eMMC chip, they are easy to identify.
Capacitors C646 and C645 are connected between USB-5V and ground. And it's true, one side of each capacitor has connectivity with ground. The other side has connectivity with the bottom-middle pogo pin.
Unsurprisingly, ground has connectivity with the bottom-right pogo pin.
For extra credit, I checked the top row of pogo pins against the adjacent resistors. R907 has connectivity with the top-left pogo pin. R905 has connectivity with the top-middle pogo pin. R906 has connectivity with the top-right pogo pin.
In fact, none of the test points are labeled on the "PinePhone mainboard top placement v1.1" drawing. And there isn't even a drawing for v1.2. Would be nice to have these things.
Wrong!
I made a bad assumption that the columns would line up. So I had PIN1 and PIN5 mixed up.
If you think about it, that makes sense given the several voltage measurements I made earlier. The bottom-left pin was always 0.2 V below my power supply, no matter what. That's because this pin connects right up to the power supply. The 0.2 V discrepancy is going to be due to resistance, or a voltage drop across U102, or even differences between the meter on my variable supply vs my multimeter.
I'm also renaming from SCL to SCK to match the name in the schematics.
The confirmed pinout is this:
Why are the pins numbered in this order? (PIN6, PIN2, PIN4, PIN1, PIN5, PIN3) Good question. Probably, the logical names for schematics were picked before the physical layout was done. So they got rearranged into the order that made physical sense.
Confirmed. You could even argue the wiki is _inaccurate_, depending on how you look at it or how picky you want to be.
Wiki:
The names "SDA" and "SCL" would be enough to connect up an I2C device. You could guess that the PinePhone is the I2C master and your device is the slave. Whatever.
The names "VBUS" and "VBAT" are far from enough to understand what these pins are for. Ok, VBUS is probably 5 V for USB. But is it an input or an output? Ok, VBAT must go to the positive battery terminal. But oops, nope, it doesn't! So what voltage should you expect to see there?
Wiki:
This description is ambiguous. Which USB? Does 5 V at up to 500 mA come from inside the phone, or are you supposed to supply that to this pin from outside?
This pin is called DCIN in the schematics!
I now have evidence that it would be safe to provide power _to_ this pin as an _input_ to the PinePhone, under one condition: You don't provide power to the USB C connector simultaneously.
It seems like it would also be OK to use power _from_ this pin as an _output_ from the PinePhone, if one of two conditions are true. 1) A 5 V power supply is connected to DCIN at the USB C connector, which means you're pulling power directly from your external USB supply, or 2) the PinePhone is driving DCIN from USB-5V via U1302, which means you're ultimately pulling power from the battery, possibly boosted up to 5 V. I don't know how much current you could draw safely.
Wiki:
This pin does _not_ connect directly to the battery. It's actually called USB-5V in the schematics!
This pin is at battery voltage _sometimes_, depending on what power sources are connected, and the operation of the PMIC and external regulators. Sometimes, this pin is at 5 V.
It seems like it would be OK to use power _from_ this pin as an _output_ from the PinePhone. I don't know how much current you could draw safely.
Wiki:
Ok, but which pin is the power input to charge the battery, and which is the power source?
My findings are that you could use _either_ of PIN1 (bottom-left) or PIN5 (bottom-middle) as a power output from the PinePhone, and you could use _only_ PIN1 (bottom-left) as a power input to the PinePhone. But only if certain conditions are met, which I already listed. And how much current you could draw or provide is unclear.
ACIN and VBUS are tied together.
There is only one, connected DCIN net.
Not true, not a problem. I reached this conclusion when it seemed that battery voltage was appearing on PIN1/DCIN.
Now we know that battery voltage appears on PIN5/USB-5V, _not_ PIN1/DCIN.
The power from the battery ends up at PS, which goes through L606, through D600, to PIN5/USB-5V. That's fine.
After this, my plan is to reassemble the phone and try applying power to pogo pins to confirm. If somebody wants me to test something while I have the mainboard in pieces, speak up now :-)
There are 3 test points at J1300. A pair of them are the USB DP and DM pins. Convert the PinePhone's USB C connector to a USB A port. The USB A's middle two pins, the data lines, have connectivity with these two test points.
The remaining test point T3 at J1300 is DCIN. It doesn't have connectivity with the USB C port because of U102. This test point has connectivity with the bottom-left pogo pin.
Now, ya have to unplug all the connectors and take the mainboard out of the phone case. And you have to remove the big metal shield covering everything up on the back.
You need the "PinePhone mainboard bottom placement v1.1" drawing to identify two capacitors C646 and C645. Once you realize how large they are, and where they are in relation to the eMMC chip, they are easy to identify.
Capacitors C646 and C645 are connected between USB-5V and ground. And it's true, one side of each capacitor has connectivity with ground. The other side has connectivity with the bottom-middle pogo pin.
Unsurprisingly, ground has connectivity with the bottom-right pogo pin.
For extra credit, I checked the top row of pogo pins against the adjacent resistors. R907 has connectivity with the top-left pogo pin. R905 has connectivity with the top-middle pogo pin. R906 has connectivity with the top-right pogo pin.
(01-03-2021, 10:22 PM)bokomaru Wrote: I don't see the pogo pins labeled on the physical mainboard.
In fact, none of the test points are labeled on the "PinePhone mainboard top placement v1.1" drawing. And there isn't even a drawing for v1.2. Would be nice to have these things.
(01-03-2021, 10:22 PM)bokomaru Wrote: If I put together the component placement drawing (or the pinout on the wiki) with the schematics, I suppose the pinout goes like this.
Code:PIN6 PIN2 PIN4
PIN5 PIN1 PIN3
or
Code:INT SDA SCL
USB-5V DCIN GND
Wrong!
I made a bad assumption that the columns would line up. So I had PIN1 and PIN5 mixed up.
If you think about it, that makes sense given the several voltage measurements I made earlier. The bottom-left pin was always 0.2 V below my power supply, no matter what. That's because this pin connects right up to the power supply. The 0.2 V discrepancy is going to be due to resistance, or a voltage drop across U102, or even differences between the meter on my variable supply vs my multimeter.
I'm also renaming from SCL to SCK to match the name in the schematics.
The confirmed pinout is this:
Code:
PIN6 PIN2 PIN4
PIN1 PIN5 PIN3Code:
INT SDA SCK
DCIN USB-5V GNDWhy are the pins numbered in this order? (PIN6, PIN2, PIN4, PIN1, PIN5, PIN3) Good question. Probably, the logical names for schematics were picked before the physical layout was done. So they got rearranged into the order that made physical sense.
(01-03-2021, 10:22 PM)bokomaru Wrote: The wiki seems unclear to me
Confirmed. You could even argue the wiki is _inaccurate_, depending on how you look at it or how picky you want to be.
Wiki:
Code:
INT SDA SCL
VBUS VBAT GNDThe names "SDA" and "SCL" would be enough to connect up an I2C device. You could guess that the PinePhone is the I2C master and your device is the slave. Whatever.
The names "VBUS" and "VBAT" are far from enough to understand what these pins are for. Ok, VBUS is probably 5 V for USB. But is it an input or an output? Ok, VBAT must go to the positive battery terminal. But oops, nope, it doesn't! So what voltage should you expect to see there?
Wiki:
Quote:The VBUS pin is powered by USB and is 5V at up to 500mA.
This description is ambiguous. Which USB? Does 5 V at up to 500 mA come from inside the phone, or are you supposed to supply that to this pin from outside?
This pin is called DCIN in the schematics!
I now have evidence that it would be safe to provide power _to_ this pin as an _input_ to the PinePhone, under one condition: You don't provide power to the USB C connector simultaneously.
It seems like it would also be OK to use power _from_ this pin as an _output_ from the PinePhone, if one of two conditions are true. 1) A 5 V power supply is connected to DCIN at the USB C connector, which means you're pulling power directly from your external USB supply, or 2) the PinePhone is driving DCIN from USB-5V via U1302, which means you're ultimately pulling power from the battery, possibly boosted up to 5 V. I don't know how much current you could draw safely.
Wiki:
Quote:The second power pin is VBAT, which connects to the battery voltage.
This pin does _not_ connect directly to the battery. It's actually called USB-5V in the schematics!
This pin is at battery voltage _sometimes_, depending on what power sources are connected, and the operation of the PMIC and external regulators. Sometimes, this pin is at 5 V.
It seems like it would be OK to use power _from_ this pin as an _output_ from the PinePhone. I don't know how much current you could draw safely.
Wiki:
Quote:The pogo pins provide access to an interrupt line, power input to charge the battery, power source and an I2C interface.
Ok, but which pin is the power input to charge the battery, and which is the power source?
My findings are that you could use _either_ of PIN1 (bottom-left) or PIN5 (bottom-middle) as a power output from the PinePhone, and you could use _only_ PIN1 (bottom-left) as a power input to the PinePhone. But only if certain conditions are met, which I already listed. And how much current you could draw or provide is unclear.
(01-08-2021, 08:38 PM)bokomaru Wrote: I found that ACIN and VBUS are allowed to be two distinct power sources, _or_ they are allowed to be connected together as one single power source.
ACIN and VBUS are tied together.
(01-08-2021, 08:38 PM)bokomaru Wrote: Now I'm not sure if they're really supposed to be one net, or actually two isolated nets.
There is only one, connected DCIN net.
(01-08-2021, 08:38 PM)bokomaru Wrote: 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?
Not true, not a problem. I reached this conclusion when it seemed that battery voltage was appearing on PIN1/DCIN.
Now we know that battery voltage appears on PIN5/USB-5V, _not_ PIN1/DCIN.
The power from the battery ends up at PS, which goes through L606, through D600, to PIN5/USB-5V. That's fine.
