BQ2970: Zero volt charging of battery with built-in protection circuit

Jason Rennie

Part Number: BQ2970
Other Parts Discussed in Thread: BQ24074,

I am sorry to ask so many questions, but I would like to double check something regarding the zero volt charging of the BQ29700.

My battery protection circuit looks like this

The rest of the power section looks like this

My battery manufacturer has UN38.3 and UL certified batteries, but only with the built in protection circuits. These batteries are delivered in a "shipping mode" that clamps the voltage to around 0.5v until a charger is connected.

Lookign at the datasheet for the BQ29700 it appears the zero voltage charging is actually disabled below 0.75v. Which I think might be a problem.

If I connect USB power to charge the battery through the BQ27074 and BQ29700, with the battery in its shipping mode, will the BQ24074 + BQ29700 be able to bring it out of shipping mode?

Thanks again for your help

-Jason

over 1 year ago

+1 Andria McIntyre over 1 year ago

TI__Expert 8526 points

Hi Jason,

Unfortunately, the BQ2970 will not allow the battery to charge if the battery voltage is < 0.75V. This will place the device in the inhibit region, which prevents 0V charging. If the BQ2970 senses a battery voltage below 0.75V, then the COUT pin will be pulled LOW, and the CHG FET will not be able to turn ON.

Best,

Andria

0 Jason Rennie over 1 year ago in reply to Andria McIntyre

Prodigy 90 points

Ok. That's very disappointing but thank you!

Are there any TI alternatives I could consider?

+1 Andria McIntyre over 1 year ago in reply to Jason Rennie

TI__Expert 8526 points

Hi Jason,

Unfortunately, we do not have a protector or monitor that can do charging on a cell starting with such a low voltage. I can assign this thread to the gauges team, though. They may be able to help if you are interested.

Best,

Andria

0 Jason Rennie over 1 year ago in reply to Andria McIntyre

Prodigy 90 points

That's ok. Perhaps there is another way to do this.

Thanks for your help, you have saved me 6 weeks and ~$500 in prototype costs!

Kind regards,

-Jason

Power management

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BQ2970: Zero volt charging of battery with built-in protection circuit