BQ40Z80: Zener not needed for Fast Cell Balancing design question?

Eohan George22

Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ76920,

I'm referencing external cell balancing mentioned here: https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/7S.pdf

Is there a reason the zeners are not needed for BQ40Z80 , but recommended for BQ76920 series ?
I haven't seen anything in the BQ40Z80 datasheet that provides extra protection for the chip.

over 6 years ago

0 Batt over 6 years ago

TI__Mastermind 42535 points

Hi Eohan,

The external balancing does not need Zeners, your current is limited in the bq40z80. The bq56920 is a very different chip with higher current thresholds, therefore the design considerations on that may be different.

0 Eohan George22 over 6 years ago in reply to Batt

Intellectual 620 points

Batt,

To my understanding, the BQ76920 chip required a zener to protect the gate of FETs for the balancing circuit from high voltages (see http://www.ti.com/lit/an/slua749a/slua749a.pdf page 7 or forum post https://e2e.ti.com/support/power-management/f/196/t/815677). This didn't sound like an issue particular to the BQ76920 chip.

Are you saying that the bq40z80 is somehow better at protecting the FETs ?

0 Batt over 6 years ago in reply to Eohan George22

TI__Mastermind 42535 points

Hi Eohan,

Fast cell balancing in the bq40zxx series gauges follows from http://www.ti.com/lit/an/slua420a/slua420a.pdf. However, looking at the post, it sounds like an added safety from the voltage standpoint that is application dependent.

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BQ40Z80: Zener not needed for Fast Cell Balancing design question?