Diode D11 prevents fast charging with 30W chargers

MNT Pocket Reform
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I have an Apple 30W USB-PD charger, which supports only either 9V or 5V. At 9V, it gives about 8.8V “real”.
That turns out to be quite the problem for the charger IC in the pocket, in combination with the diode D11. While it’s a Schottky diode, at ~9V and 1A it has about 0.3V voltage drop.

The MP2762A charger IC switches between boost and buck charging “when the input voltage exceeds 8.5V”.

8.8V - 0.3V = 8.5V

And indeed I can see the charger trying to switch to buck charging (fast), but then the voltage drops below 8.5V, and it goes back to boost charging again (very slow). And then the cycle repeats.

For testing, I’ve bridged D11 with a clamp, and immediately the charger switches to buck charging and stays there.

The MP2762A datasheet shows a “typical application circuit” where the 10mOhm R1 (fronting IN) is immediately connected to the USB port. From the results above, it would seem like that is not just typical but actually necessary :frowning:

Ping @minute :slight_smile:

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Now documented here Charger Mod/Fix for Next Rev Hardware: Use OTG function of MP2650 (#3) · Issues · Reform / MNT Pocket Reform · GitLab

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I know this hasn’t been validated / tested thoroughly, but does this imply that it may be possible to charge from 30W chargers with a small hardware modification?

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Yes. There are however open questions regarding charging speed. But it does work!

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