Pogo pins power clarification - reading schematics
02-28-2021, 06:02 PM
Correcting myself about D600...
Not a zener diode, it's a "Schottky Rectifier" or "Schottky Diode". (The symbols are similar)
https://en.wikipedia.org/wiki/Schottky_diode
Also see the datasheet for the SS24. (I found one on Digikey or something)
See attached screenshot from the SS24's datasheet. The drop will vary with current, and by extrapolating beyond the limits of this graph, at less than 100 mA, the voltage drop is less than 0.25 V; decreasing more as current decreases. I don't know how this interacts with the LP6226; maybe as a whole, the SS24 and LP6226 make up a "perfect" regulator or "super" diode.
Another screenshot attached, showing that "reverse" current won't exceed 10 mA until we exceed 120 V. (which I would call the "breakdown" voltage for a zener diode)
The datasheet says "These rectifier are suited for free wheeling, secondary rectification, and reverse polarity protection applications."
That being true, _maybe_ you could supply power at pogo pin #5 as an input to the Pinephone, _if_ the LP6226 is disabled. I still don't think it should be done.
Unlike for DCIN, there is no "detection" logic that would allow us to determine whether or not an external power source is connected to pogo pin #5. There would have to be cooperation with software to ensure that PD8-VCC5V_EN is "off", and I'm not sure how we would do that, other than by manually controlling it. Or by permanently hogging it to "off", making us unable to act as a USB host while on battery power (no voltage boost to 5 V).
(02-28-2021, 03:37 PM)bokomaru Wrote: (1) If you supply power at pogo pin #5, current could travel backwards across the zener diode D600, connecting a power input the the PS output of the AXP803. This depends on the actual voltage provided at pogo in #5, and on the zener breakdown voltage of D600.
Not a zener diode, it's a "Schottky Rectifier" or "Schottky Diode". (The symbols are similar)
https://en.wikipedia.org/wiki/Schottky_diode
Also see the datasheet for the SS24. (I found one on Digikey or something)
(02-28-2021, 03:37 PM)bokomaru Wrote: What should the voltage drop be across D600? We haven't looked it up.
See attached screenshot from the SS24's datasheet. The drop will vary with current, and by extrapolating beyond the limits of this graph, at less than 100 mA, the voltage drop is less than 0.25 V; decreasing more as current decreases. I don't know how this interacts with the LP6226; maybe as a whole, the SS24 and LP6226 make up a "perfect" regulator or "super" diode.
(02-28-2021, 03:37 PM)bokomaru Wrote: Unless you can show that, for example, 5.3 V at USB-5V would not flow backwards across zener diode D600 to PS, a power source should not be connected as an input to the Pinephone at pogo pin #5.
Another screenshot attached, showing that "reverse" current won't exceed 10 mA until we exceed 120 V. (which I would call the "breakdown" voltage for a zener diode)
The datasheet says "These rectifier are suited for free wheeling, secondary rectification, and reverse polarity protection applications."
That being true, _maybe_ you could supply power at pogo pin #5 as an input to the Pinephone, _if_ the LP6226 is disabled. I still don't think it should be done.
Unlike for DCIN, there is no "detection" logic that would allow us to determine whether or not an external power source is connected to pogo pin #5. There would have to be cooperation with software to ensure that PD8-VCC5V_EN is "off", and I'm not sure how we would do that, other than by manually controlling it. Or by permanently hogging it to "off", making us unable to act as a USB host while on battery power (no voltage boost to 5 V).
