Hi,
We are using BQ20Z655-R1 IC within our battery packs has 4 series cells, voltage ranges are beetween 10 and 16,8V. And the mosfets are FDS8813NZ N Channel Power Mosfet which suggested at IC's datasheet. The battery packs are discharged at Low Temperature (-22 °C) and High Tempereture (+55°C). At High temperature test, thats ok no problem. But at the low temperature tests, the mosfets failure and becomes short circuit.
I did some conversation with Fairchild and they say that mosfet should work at -22°C, you can check the VGS voltage at the low temperature.
Before discharging at low voltage again, i did some tests at room temperature 25°C. Let's says that overcurrent limit is 12A, time is 1second, i discharge the battery with 13A and mosfets turn off after 1 second in the voltage ranges 10 - 16,8V. But beetween 5 - 10V supply discharging with 13A, mosfets could not turn off and becomes short circuit and burns.
So the main reason of mosfets failure is low voltage. You know that when discharge the lithium ion battery at low temp, battery has low power and voltage.
What should i do, can i change the IC or mosfets?
Look forward to your quick replies,
Best Regards,
John.