Any help with BQ27425A laptop battery controller?

Thread Starter

Michele Shin Abruzzese

Joined Jul 11, 2017
Hi there!

I plugged my AC adapter into my laptop with a reverse polarity. Fortunately my laptop still works but it doesn't charge battery anymore and it doesn't work with AC adapter only. It draws very small current from it (around 1 or 2 milliamps) but enough for the system to recognize it connected and "charging" but a lot less than 2,47 A it requires to work.

I opened the laptop and with a tester I found out there's a mosfet (M3024M) right after the positive plug that drops the voltage from 19V to around 1V and I think it might be the problem. The mosfet is driven by the BQ27425A battery controller which for what I know regulates the switching between AC adapter and battery, checks its charge, protects the system from overvoltage/overcurrent and things like that.

Now the datasheet shows a schematic where in order to obtain a reverse polarity protection, a third mosfet is placed after the first two. I checked and my laptop has just 2 of them at the AC adapter input.

Does it mean that it doesn't have a protection against polarity inversion?
If it doesn't have a protection, where do you think is the damage?

The controller seems to work fine since it correctly shows the battery charge and detects the AC adapter connection. Is there a way to test it?

If someone has any kind of suggestion it'd be really appreciated!