BQ76952: Charge MOSFET failing when charging cutoff by BMS

Shyama Agrawal

Part Number: BQ76952

Hello,

Our BMS uses BQ76952, the discharge MOSFET's behavior is good when discharge FET is turned OFF during short circuit event. Now, we are facing issue with charge MOSFET turn OFF when COV is triggered (Interrupting a current of 25A), the charge MOSFET keeps on failing (Discharge MOSFET doesn't fail).

Please let me know what can be the cause, the charger we are using is a simple CC-CV charger which might produce some overvoltage when the BMS suddenly cuts off the charging current. I can send you the schematic on personal message if needed.

over 3 years ago

0 Matt Sunna over 3 years ago

TI__Guru* 81034 points

Hi Shyama,

When you say the CHG FET fails, do you mean it is destroyed? Or do you mean it does not switch as expected? Is your FET rated for the current and voltage of your system?

I will send you an E2E connection request so you can share your schematic if needed.

Best regards,

Matt

0 Shyama Agrawal over 3 years ago in reply to Matt Sunna

Intellectual 860 points

Hi Matt,

The MOSFET is destroyed. The MOSFETs are rated at 100V, 100A (3 parallel both for charge and discharge). Battery Voltage is limited at 68V.

0 Matt Sunna over 3 years ago in reply to Shyama Agrawal

TI__Guru* 81034 points

Thanks for sharing the schematic image - I got your private message. I will look over it and reply in the private message.

0 Jessica Riley2 over 3 years ago

Prodigy 220 points

Were you able to figure out the route cause of this issue?

0 Matt Sunna over 3 years ago in reply to Jessica Riley2

TI__Guru* 81034 points

Hi Jessica,

There were some issues in the schematic that were identified (incorrectly sized gate resistors on the FETs, capacitors on the FET gates). I believe Shyama was going to make these changes to verify the problem was resolved. This document offers good circuit examples for driving multiple FETs: https://www.ti.com/lit/pdf/sluaa09

Best regards,

Matt

0 Jessica Riley2 over 3 years ago in reply to Matt Sunna

Prodigy 220 points

Thanks for the response Matt

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BQ76952: Charge MOSFET failing when charging cutoff by BMS