Increasing the maximum power draw
#11
(05-28-2021, 09:02 AM)megous Wrote: dsimic: I've bought and checked with a better 5A cable. Now the voltage at the Type-C connector is 4.9V at max load, so the max PBP can draw from DC/Type-C VBUS is 11.34W (that's what I measured).

So that's the same as your theoretical 11.4W limit. Smile

Thank you very much, megous, for the power draw measurement!

The good news is that the BQ24171 works as configured.  That bad news is that the total power draw "from the wall" is much lower than what can be provided by the official barrel port charger or a USB PD charger in its default configuration. Sad  They're both capable of providing 15 W.
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#12
Slightly OT, but is there also a way to limit the charging to preserve battery-life? Like keeping the battery at 50-70% charge only?
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#13
The good news is that it should be possible to tweak the desired maximum battery charge level by adjusting the BQ24171's target battery voltage, which is described on page 16 of the BQ24171 datasheet.  However, there are some bad news:
  • The target battery voltage is configured using a couple of resistors on the PCB, so those would need to be replaced.
  • Reducing the target battery voltage and leaving the maximum battery charging current unchanged would result in further reduction of the maximum power that can be taken from any of the two power inputs, and the battery would even more often be used as the power source for the laptop, even if it's connected to a charger.
  • The above-described issue could be mitigated by increasing the maximum battery charging current at the same time, but unfortunately there isn't a lot of room for that.  However, there might be a sweet spot.

By the way, after further analysis of the way BQ24171 is used in the PineBook Pro, I'm pretty sure that increasing the maximum battery charging current is the only doable way for increasing the maximum power draw from any of the two power inputs.  All components in the power path should be able to handle a 15% to 20% increase of the maximum battery charging current; combined with additional cooling applied to the BQ24171, this should be a win-win hardware modification.

Of course, I still need to re-evaluate the entire approach a few more times, so we definitely stay on the safe side with such a modification.
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