11-26-2020, 02:20 PM
(11-20-2020, 11:51 AM)battery charging ICxyzzy Wrote: Anyway, a new PCB rev that will draw more than 3A from the DC barrel connector isn't really viable, since it wouldn't be possible to connect any of the existing power adapters without overloading them. It's not possible to just just "draw less" from the 3A adapter. The charger will try to draw more and the adapter will be unable to keep at 5V and drop voltage, or totally lose regulation, or trip a thermal fuse, or (I see the pine supplied adapter is not UL-listed!) catch fire.
I think what could be done is the program the FUSB302 to allow 5V, 9V, or 12V from the type-c connector with USB-PD. The battery charger can handle an input up to 17V. The input side current wouldn't need to be any higher. If I understand the charge circuit right, VCC_SYSIN will be regulated to the battery charging voltage, i.e. about 2V-4.4V, by the switching regulator in the BQ24171. So nothing past the input side of the BQ24171 will see a higher voltage if VCC_5VIN is raised up to 12V. That means none of the other regulators or the PMIC need to worry about >5V input. Only the charge LED will see it. Probably fine, it should be possible to chose a current limit resistor so that 5V is visible and 12V doesn't burn it out. And the circuits, which I don't totally follow, to prevent shorting between VCC_DCIN and VBUS_TYPEC would need to be able to deal with it.
You're right, it would be pretty much impossible to reliably determine the type ("standard" or "high current") of the charger connected to the barrel connector. We'd need a separate signal/wire for the type identification, which is simply not an option.
Altering the built-in Type-C PD controller is a really great idea! I'll have a detailed look into it and report back here. There might be some other minor issues related to the increased voltage received from a USB PD charger; for example, it might be required to also modify the circuitry that adjusts the current configuration resistors for the battery charging IC when a PD charger is connected vs. when using the barrel connector.
