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BQ29209: BQ29209 Faul Condition. 23.8mA current flowing through VC1 Pin2.

Part Number: BQ29209
Other Parts Discussed in Thread: STRIKE


Our quality assurance team found that there were battery pack with discharged batteries after some time and I was investigating the issue. During investigation I found that on U3 VC1 pin there were 23.8 mA discharge BT3 which is Independed to the battery voltage as I emulated battery cells with precise power supply. As I understand this pin is used for voltage sensing and is High Impedance Input with current around few uA.

The Circuit:

The sequence of soldering batteries as far as I know was BT1 -> BT2 -> BT3 - BT4.

I would be grateful if you could give some thoughts what could be the root cause of such an issue, so we could implement design changes or preventive actions.

  • Hello Mantvydas,

    This is a very strange set-up. Each IC is monitoring two batteries? It seems the bottom IC is not correctly set-up. This part is meant to protect/balance two cells, VC1 of U8 is at ground.

    You confirmed the current is flowing through VC1, not VC1_CB right?

    If the IC is replaced, is there still a high current draw? If so, the device may have gotten damaged.

    It is hard to know how the IC may have gotten damaged, in what conditions did it get damaged, how many units have been found with this? 

    Best Regards,

    Luis Hernandez Salomon

  • U8 is balancing BT1 and BT4 from another battery pack 

    Yes, the current was though VC1, I measured it through R14 resistor. 

    When I replaced IC the issue disappeared so the IC probably was damaged. At the moment we have 2 units  like this.

    It is interesting how this damage could occur, is it only overvoltage condition?

    Maybe you have so research on how different pins got damaged on overvoltage condition and what was their behaviour?

  • Hello Mantvydas,

    It is hard to tell how it became damaged, it could be due to voltage transients, it could have been during cell attachment, or maybe due to an ESD strike.

    If you find the damage is consistent to this IC and same VC1 pin, then you could potentially add a Zener/Schottky pair to attempt to protect this pin from damages.

    Best Regards,

    Luis Hernandez Salomon