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BQ34Z100-G1: Reverse Connection of Sense Resistor to SRP and SRN

Kurt Aronow
Prodigy 60 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQ34Z100,

Tool/software:

Hello,

I'm doing a new design in which the BQ34Z100-G1 battery fuel gauge is on a circuit board with a battery charging circuit, not in a battery pack.  If I just ground the minus side of the battery, there's nowhere to attach the current-sense resistor for the BQ34Z100.  Since the SRN input shouldn't go below ground, I want to tie the battery minus to the current sense resistor and the other side of the current sense resistor to circuit ground (also the ground of the battery charging circuit).  This means that I need to tie the SRN input to ground and the SRP input to the current sense resistor which is opposite from what is shown in the application circuit in the data sheet.  Will this cause a problem with the BQ34Z100-G1 operation, or will this allow the fuel gauge to work as expected?

Thanks!

Kurt

  • 0
    TI__Mastermind 26395 points

    Hello Kurt,

    The easiest way to think about the current sense resistor and how it should be tied into the schematics is that it would go sereies with the Pack(-) >> Sense Resistor >> Battery(-). In this case Ground would simply be the battery(-) but the role of the sense resistor is to carry the load on the low side of the battery.

    Thank you,
    Alan 

  • 0
    TI__Mastermind 26395 points

    Hello Kurt,

    The easiest way to think about the current sense resistor and how it should be tied into the schematics is that it would go sereies with the Pack(-) >> Sense Resistor >> Battery(-). In this case Ground would simply be the battery(-) but the role of the sense resistor is to carry the load on the low side of the battery.

    Thank you,
    Alan 

  • 0 in reply to Alan Frias
    Prodigy 60 points

    Hello Alan,

    Thanks for the reply.  I understand what the drawing from the datasheet is telling me, i.e., pack- to sense resistor to battery.  However, in my case, the battery is already in a pack.  So, I want to connect Battery minus => sense resistor => ground.  In order to make this work I will connect the SRP pin of the fuel gauge to the top of the sense resistor and the SRN pin to ground (other side of the sense resistor).  Do you see a problem with this?

  • 0 in reply to Kurt Aronow
    TI__Mastermind 26395 points

    Hello Kurt, 

    You are correct you would connect BATT(-) >> Sense resistor >> Load (-), the only thing to keep in my is that you want your SRP and SRN connection to be the closet possible to the sense resistor as well as minimize the voltage drop through keeping the traces short or adding more pour to the trace.

    Thank you,
    Alan