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BQ76952: Cell sensing series resistance getting open (burn)

Kushal Pal Singh
Prodigy 30 points
Part Number: BQ76952
Other Parts Discussed in Thread: STRIKE

Tool/software:

Hi team,

 I am using BQ76952 in 16S configuration, some time I am observing cell sensing series resistance getting open.

I have used 100 ohm 0603 package 100mW resistance.

I am using BMS with LFP battery, so during cell balancing at maximum voltage (3.65V) power dissipation across 100 ohm resistance will be around 34mw.

Please find the below snip of cell sensing circuit.

  • 0
    TI__Mastermind 42060 points

    Hello Kushal,

    When do you see these resistance being blown? Is it during balancing? Or does it happen during any other case?

    I would not imagine that balancing would cause problems, the wattage due to balancing would be closer to ~26-mW, which should be well below its max wattage rating. 

    My assumption is that some other transient/current would cause the damage. Like an ESD strike.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Prodigy 30 points

    Hello Luis, 

    Thank you for reply. I am observing failure just after inserting cell sensing connector into the PCB.

    Apart from ESD do you see any other cause of failure?
    What you will suggest to add on cell sensing lines to protect from ESD?

  • 0 in reply to Kushal Pal Singh
    TI__Mastermind 42060 points

    Hello Kushal,

    Do you have any load attached to the top-of-stack of the battery stack? If there is a load attached, it could be possible for some current to flow momentarily, depending on how the cells are attached, through the internal body-diode of the cell balancing FETs. 

    To protect against ESD/Hot-plug transients, you may add some capacitance before the sense input resistances, these could go to Vss for best effect. I've also seen the addition of Zeners across the VCx pins to keep transients low.

    Best Regards,

    Luis Hernandez Salomon