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BQ79656-Q1: BQ79656-Q1 GND design

akihiro_kakishima
Prodigy 10 points
Part Number: BQ79656-Q1
Other Parts Discussed in Thread: BQ76952

Hello Sir:

We are considering BQ79656-Q1 in our  BMS.

I' d like to confirm about GND position for IC.

According to Datasheet Fig.10-1.(P187), GND position is under side of Rsense.

But if  it put this side, Vsense affects all sensing parameters.

GND position for IC is suitable for upside of Rsense ?

Best regards.

 

  • 0
    TI__Expert 3760 points

    Hi,

    The SRP/SRN pins are intended to be used for current sensing for the system. That is why the GND position is depicted like that. If SRP was connected to GND there would be no measured current. The cell voltages are all measured as differentials, so the small voltage difference across the SRP/SRN pins won't make significant difference on those measurements. The Rsense will dissipate some power but shouldn't affect the sensing. 

    Best,

    Nancy

  • 0 in reply to Nancy Hidalgo
    Prodigy 10 points

    Hi Nancy

    Thank you for your reply.

     

    I understood your point.

    But BQ79656 datasheet shows system GND.

    So, I thougt it need to separate GND design.

    like this,

    SRP side is for IC GND. SRN side is for system GND(Cell Pack -).

    For example, reffering to BQ76952 datasheet, it suggests that diagram.

    Best regards.

    akihiro

  • 0
    TI__Expert 3760 points

    Hi,

    I see. In the diagram this device is the lowest device in the daisy chain and connected to a current sense resistor. The SRN is usually grounded to the PCB ground of the BQ79656 board which in turn is usually connected to PACK- (because it’s the lowest device in the stack).

    Best,

    Nancy Hidalgo