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BQ20z95 short circuit problem

Jan Schreibeis
Prodigy 30 points

Hi,

we are using the BQ20z95 in a battery pack design. While performing short circuit tests we ran into following problem.

The problem is that after attaching the short circuit condition BQ20Z95 gets damaged and the dischargefet pin doesn't work anymore. Communication shows that both FET pins should be high, but the dischargefet pin remains at low state and doesn't come back. Shortcircuit currents are as high as 150A and we have a sense resistor of 5mOhm. Picture shows the circuit we built our design on.

In the datasheet we found that BQ20Z95 absolute maximum rating at Pin GSRP is -0.3V to Vreg25+0.3V. If we have 150A flowing through the 5mOhm sense resistor in discharge direction we have a voltage of -0.75V at GSRP. Could that be the reason for BQ20Z95 to get damaged? Is there a possible solution to this problem? Why is Pack- = GND in your example design? In other designs Batt- was GND.

Thanks in advance.

Jan