BQ2057WTS battery reverse and short connection protection

[Prayer]

I designed a battery charger for 2 cell Li-po with BQ2057WTS as you can see "bq2057wts" picture attached. I have to short circuit protection and reverse connection protection for battery connection. I added a schottky diode as you can see "bq2057wts revised" picture attached but it didn't solve reverse connection. When I connected battery reverse, the IC burned.
I thinked to use P or N channel mosfet but I didn't realise that. Could you suggest a solution for this project ?

[HalfSpace]

Hi Prayer,

The attached circuit should work for short circuit and reverse protection of the chargers output connections. The only thing is R3’s value which protects U1 pin 2 (BAT) from reverse voltage. I cannot find the input current required for this pin under normal operation so there could be a voltage drop across R3 which may change the charging voltage. If the chargers output connections are shorted M2 will turn off followed by M1 disconnecting the output. The same with battery connected in reverse to the charger M2 will turn off followed by M1. The led D1 will light in ether condition. If D1 is not required a 10k resistor across the PMOS is required.

HalfSpace 

[Prayer]

Hi Halfspace

First of all thanks for your attention. I did a circuit like your suggest circuit. The difference is I controlled this circuit via microcontroller. I have to ask a question. I don't need D1 but I didn't understand where I have to put 10 k resistor. Is it PMOS's S and D pins like D1 and R4 ?

[HalfSpace]

Hi Prayer,

The 10k resistor replaces D1 and R4 (see circuit attached).

HalfSpace 

[Prayer]

Yes, I understand well but I want to know why it is there ?

[HalfSpace]

Hi Prayer,

The 10k resistor is to make sure the PMOS turns on when no battery is connected. Pin 2 (BAT) should follow the output of Q1 like on the original circuit.

HalfSpace 

[Prayer]

Hi HalfSpace

Thanks for your explanation and helps for this project.

[macboy]

Very simple reverse protection can be done with a fuse followed by the reverse-biased rectifier diode. If the battery is connected backwards, the diode basically shorts it out across the fuse, which blows. This is crude but effective. It is designed to save the charger, not the battery, and will stress the battery a little until the fuse opens.