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BQ40Z80: BQ40Z80 reverse pack voltage leads to damage to MOSFET

Part Number: BQ40Z80

Hi team,

My customer encountered a issue when they add reverse pack voltage on BQ40Z80. They find the MOSFET will be burnt.

However they have added the reverse-protection circuit. And they used 60V VDS Mos. 

It is a 6S6P project which used Li-ion cells. The charger voltage is 25.2V. So even if the pack voltage add to battery voltage it won't over 60V.

The attachment is their schematic for MOSFETs. Do you have any suggestions for this issue?

BR,

Steven

  • Hello Cherry,

    Are the tests being done with the batteries inserted so the gauge is powered? Are the FETs damaged by the current through the body diode or other cause?

    I'm not sure how much this is related to the gauge compared to the BMS as a whole, they may have some incorrect biasing on the reverse polarity protection that's causing undesired current to flow and damage the FETs.

    Sincerely,

    Wyatt Keller

  • Hi Wyatt,

    Yes, the gauge is powered. Because the voltage is not enough to damage the MOSFET so I think it is caused by the current through the body diode.

    What's the meaning of some incorrect biasing on the reverse polarity protection? If it is caused by current why they didn't observe the damage when apply forward direction voltage?

    BR,

    Steven

  • Hello Steven,

    I'm not familiar with the parts used on their reverse polarity protection, I was pointing out that it may not be the gauge but the external circuitry that is damaging the FETs. It looks like when the batteries are reverse connected the circuitry sets VGS to 0V essentially. Are both the CHG and DSG FETs damaged?

    Sincerely,

    Wyatt Keller