BQ76940: 26 cell management with BQ76940

David Kim

Prodigy 50 points

Part Number: BQ76940
Other Parts Discussed in Thread: BQ76930

Dear,

I am novice about designing BMS with TI products. I found BQ76940 which supports 15 series cell.

Is it possible to design 26 series cell for E-Bike with two BQ76940 chips? and any reference documentation and circuit?

And I am not quite sure about the difference between high side and low side FET control with BMS chip.

which one is more popular and chiper?

Thanks in advance,

over 2 years ago

+1 Luis H. S. over 2 years ago

TI__Mastermind 33520 points

Hello David,

Welcome! Yes, this is possible.

We have a reference design for the BQ76930, TIDA-01093, which is from the same family as the BQ76940 (the BQ769x0 family).

You could stack two BQ76940 in the same way.

Regarding Low-Side vs. High-Side, this is a common question, these older e2e threads may be helpful: https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/784837/bq76920-low-side-switching-or-high-side-switching-which-one-should-prefer-and-why

I hope this helped!

Best Regards,

Luis Hernandez Salomon

0 David Kim over 2 years ago in reply to Luis H. S.

Prodigy 50 points

Thanks, Luis. This is very helpful for me.

0 David Kim over 2 years ago in reply to Luis H. S.

Prodigy 50 points

Thanks, Luis. I got the reference documentation for using BQ76940 as you mentioned. But I couldn't find the way to read the pack current though I2C from BQ76940. They just supported Coulomb Count with register. Do I need to find another method?

Thanks in advance.

0 Luis H. S. over 2 years ago in reply to David Kim

TI__Mastermind 33520 points

Hello David,

To read the pack current, you would have to get the 16-bit ADC reading of the coulomb counter and convert it to an analog voltage.

Then using Ohm's law, you can find the current by using the sense resistor value: current = V_ADC/R_SENSE.

See Section 10.3.1.1.3 16-Bit CC of the datasheet for more guidance.

Best Regards,

Luis Hernandez Salomon

Power management

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BQ76940: 26 cell management with BQ76940