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BQ76952EVM: Question about floating of SRP inside the PCB.

Eric Zhang
Prodigy 80 points
Part Number: BQ76952EVM
Other Parts Discussed in Thread: BQ76952, BQ76972

Tool/software:

To whom it may concern,

I am developing the BMS system with BQ76972 (or BQ76952). In the evaluation board, the current will flow through the PCB thorough the BAT- trace. Since the BAT- trace is tied to VSS through NT1 net tie, which makes both the Cell 1N (the bottom wire of battery pack) and the left of current shunt resistor R30 (the SRP input) connected to VSS. 

In my application, the battery negative wire (high current pass) is not through our board, which means the current shunt R30 is external to our PCB. In this case, I don't want to connect both Cell 1N and the input of SRP to the VSS on our PCB to form another path of current through our PCB (I would like to have all the current through the external BAT- cable). In this case, could I just connect Cell 1N to the VSS on the PCB, and leave SRP input to be floating on the PCB? If for some applications, we don't use BQ76972 to measure the current where the BAT- cable doesn't exist, will the floating of SRP input damage the BQ?

Thanks.

Regards,

  • 0
    TI__Genius 17755 points

    Hello Eric,

    It is recommended that if the SRP is not being used, the pin should be connected to pin 17 (VSS). More information about unused pins can be found in Table 16-3. Terminating Unused Pins in the BQ76952 Datasheet.

    If the SRP pin is not biased to VSS then there will be inaccuracies when measuring current across the sense resistor and also the voltage on the SRP could float up or down.

    For your specific application, if you’re not measuring the current, a zero-ohm resistor could be used instead to short the SRP to VSS, and you could leave it unpopulated if you want to have current measurements.

    Best Regards,
    Alexis