BQ2970: When Battery voltage is < Underlockout voltage, BQ25101 doesn't charge it

Rémi Bouteiller

Part Number: BQ2970
Other Parts Discussed in Thread: BQ25101,

Hello,

I have a circuit composed of a BQ25101 Lipo Charger with I_OUT set to 10mA and a BQ29700 protection chip.
This circuit is made to have a very low power consumption and board size.

When Battery is above 2.8V, it's working well, charger could charge it at 10mA, board is working.

But when battery is below 2.8V, over-discharge protection comes in and even with charger connected, it doesn't work.
Voltage between BAT and GND is 1.3V
Current sunk from power supply is 2.7mA (the rest of the board is under 500uA)

I have no idea what the problem could be.
Please tell me if more information is needed.

Thanks for your help

8 months ago

0 Andria McIntyre 8 months ago

TI__Expert 8461 points

Hi Remi,

I can't see the component values for your schematic. Can you let me know the capacitances and resistances of each component?

Overall, the BQ2970 part of the schematic looks okay, but I agree that the behavior you are observing is odd. If the device is consuming copious amounts of current, the part may be damaged. Are other units exhibiting this behavior?

Additionally, you can create another post to check the charger connections with the chargers team.

Best,

Andria

0 Rémi Bouteiller 8 months ago

Prodigy 10 points

Hi Andria,
Thanks for your answer, I just find the problem thanks to this post : https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/622007/bq2970-can-t-charge-even-the-battery-voltage-is-2-83v

The charge current was set to 10mA on the BQ25101, when I change R_iset to 5.1kohms (charging current 26mA) everything work as expected.
But I still don't know why it's not working with 10mA

0 Andria McIntyre 8 months ago in reply to Rémi Bouteiller

TI__Expert 8461 points

Hi Remi,

I am glad to hear that increasing the charging current addressed your issues. The BQ2970 does not have any protections that will be triggered with low current, and the voltage differences you cited in your original post should be able to disable over-discharge protections.

This may be an internal design feature, but for now I recommend continuing to charge with a higher current.

Best,

Andria

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BQ2970: When Battery voltage is < Underlockout voltage, BQ25101 doesn't charge it