11-20-2020, 11:51 AM
Other stuff would need to change to get >3A from the battery charger. The output inductor, L1, is 3.3 µH while for 4A the typical value would be 2.2 µH. Also likely changes to the input and output caps. The MOSFET, U40, would need to be able to handle the current too.
There's also the thermal limits of the charger controller, the MOSFET, other current switching FETs, etc. Just because the absolute limit in the datasheet is high enough doesn't mean the PCB layout is adequate to keep the thermal resistance low enough to reach that limit.
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.
There's also the thermal limits of the charger controller, the MOSFET, other current switching FETs, etc. Just because the absolute limit in the datasheet is high enough doesn't mean the PCB layout is adequate to keep the thermal resistance low enough to reach that limit.
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.
