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BQ34Z100-R2: About the EVM schematic

Mauricio Correa
Prodigy 70 points
Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: BQ34Z100EVM

Tool/software:

In the EVM schematic you can see that GND and AGND are placed on BAT-. But I think it would be better to put it on PACK-, so that the "GND" would be at the same point as the charger and the reader circuit (processor). What do you think?
Can Texas supply the Sch/Pcb in CAD format?
Thanks in advance for your answer.
Mauricio.

                       

  • 0
    TI__Genius 17345 points

    Hi,

    The GND and AGND need to be on the BAT- pin, I recommend following the EVM GND scheme.

    The Layout Guidelines section in the DS has more information on layout recommendations.

    BQ34Z100-R2 Wide Range Fuel Gauge with Impedance TrackTm Technology datasheet (ti.com)

    Unfortunately, I cannot share the CAD/Gerber files for the EVM.  The EVM users guide has images of the internal layers of the EVM.

    bq34z100EVM Wide Range Impedance Track Enabled Battery Fuel Gauge (Rev. B) (ti.com)

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 70 points

    Thanks Evan;
    But in this case, the current consumed by the circuit (e.g. from the EVM) does not go through the shunt (R30). Is this correct? Isn't that a problem?
    I look forward to your answer.
    Sincerely, Maurício

  • 0 in reply to Mauricio Correa
    TI__Genius 17345 points

    Hi Mauricio,

    The R30 sense resistor measures the charge and discharge current from the battery. This is not a problem, it is intended to function this way, the gauge measures the voltage drop across the SRN/SRP pins.

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 70 points

    Hi Evan. Thanks for your reply.
    Sorry for my insistence, but according to the block drawing above in the original question, the orange square on the right, "SystemMonitoring", refers to the BQ34Z100EVM circuit, where the power supply for the EVM circuit is only connected from BAT+ to BAT-; therefore, this consumption does not go through R30 and is not accounted for by the BQ34Z100-R2. The GND of the rest of the circuit, including the charger circuit plus the processor circuit, is on PACK-, so the charge and discharge current flows through R30, and the BQ34Z100-R2 does the accounting.
    If you think that this consumption, that of the BQ34Z100EVM circuit, is not significant, we can proceed as indicated in your last reply.
    Thank you for your patience, I look forward to your reply.
    Sincerely, Maurício

  • 0 in reply to Mauricio Correa
    TI__Genius 17345 points

    Hi Mauricio,

    Can you share a full schematic of your BMS for verification.

    If you would prefer to send it privately, this can be arranged.

    Regards,

    Evan

  • 0 in reply to Diego
    Prodigy 70 points

    Hi Evan, Thanks.
    We are still developing a complete schematic of the battery control circuit. Hence the doubts. Our doubt is about the BQ34ZEVM circuit.
    We have the BMS block diagram shown below. For the monitoring part, we'll use the schematic of the BQ34Z100EVM circuit, just the part inside the blue line in the EVM schematic. The BQ34Z100EVM circuit says to connect the "GND" of the EVM circuit to BAT-, as shown by the red line in the block diagram (in the block diagram inside the system monitoring square). We wonder if it wouldn't be better to connect it to PACK-, as shown by the yellow line, so that the current from the EVM circuit would also go through R30, and that current would also be accounted for by bq34z100-R2. Or is the current so small that we can ignore it?
    I'm hoping it's possible to analyze this using the block diagram alone.
    Thanks in advance for your answer.

    BMS-Block Diagram.pdf

  • +1 in reply to Mauricio Correa
    TI__Genius 17345 points

    Hi,

    Thanks for the additional description, I understand the confusion now.

    So, we do not want the current from the EVM circuit to flow through the R30 sense resistor. The R30 sense resistor is used to measure the current leaving and entering the battery only. Adding the EVM circuit current will throw off the gauge current readings and overall, SOC/SOH calculations. I recommend following the scheme in the EVM with GND/AGND on BAT-.

    Regards,

    Diego

  • 0 in reply to Diego
    Prodigy 70 points

    Thanks for your reply, Diego;
    Then we'll do it this way.
    Sincerely, Mauricio.