BQ40Z80: Increasing Shutdown Threshold with Series Zener

Antonio Fadhel

Part Number: BQ40Z80

Hi,

My customer is having an issue with residue output voltage not allowing their bq40z80 to go into shutdown when the cells go below their SUV threshold. Leakage current from their FET switch is keeping the output voltage at a level above the 2.2V min operating voltage for the device. The PACK input sees this voltage and prevents the device from going into shutdown mode.

Can they add a Zener diode in series with the PACK pin to increase the threshold from 2.2V to Zener Voltage (10V) + 2.2V?

Thanks,

Antonio

over 5 years ago

0 Kang Kang over 5 years ago

TI__Mastermind 24870 points

Hello Antonio,

Can you provide the part number of the FET and are they connecting it the same way we have on our EVM? Also the zener diode, can you provide a part number there as well?

0 Damian Lewis over 5 years ago

TI__Mastermind 34775 points

Antonio,

Do you have a schematic that you can share? It's not clear to me how when you FET is off leakage current from the FET prevents shutdown. It's most likely capacitance on the PACK+ or bq40z80 PACK pin is holding up the voltage and preventing shutdown. Adding a Zenner to PACK pin will help shift the wake up threshold, but may impact the FET safety turn off time.

A schematic would help us better understand the root cause and give the best recommendation.

0 Antonio Fadhel over 5 years ago in reply to Damian Lewis

TI__Genius 9410 points

Thanks, Damian. I will share more details offline.

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BQ40Z80: Increasing Shutdown Threshold with Series Zener