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bq34z100-G1: SRN and SRP pins

hwswdesign
Intellectual 310 points
Part Number: BQ34Z100-G1
Other Parts Discussed in Thread: BQSTUDIO

Question #1 - The bq34z100-G1 simplified implementation shown in Figure 14 of the datasheet is the case where the bq34z100-G1 is part of a pack.

In my system, I already have a pack, which contains the cells and all the protection circuitry, so I only see pos and neg terminals

I think in my system I should connect the SRP/SRN pins as shown in the attached file "FuelGaugeConnection-201708161342.pdf". I connected SRN to ground, because the current flow would not be correct if SRP is connected to ground. Figure 14 of the datasheet shows SRP connected to ground, which would not work in my system.

Any problem with connecting SRN to ground?

FuelGaugeConnection-201708161342.pdf

Question #2 - In reality, I connected SRN/SRP opposite what I showed above. I believe the part won't be damaged, but it will see charging as discharging, and visa-versa. Is there any way to "fix" this is software? Like maybe programming things with a reversed sign?

Question #3 - In these forums I saw a question about updating firmware in the bq34z100-G1. I did not see anything about this in the datasheet. Is this something I should design for, and if so, how do I do that?

.

  • 0
    TI__Guru* 76230 points
    1. and 2. Connecting SRN to ground inevitably means your current polarity will be swapped. Charge will be negative, discharge will be positive. Even though you have protective circuitry for your pack, i do not see how that differs from the circuitry of in the data sheet. You should connect SRP to ground,
    3. You can update the firmware with either an srec or flashstream file. pls see link below and review the EVM user guide of the device.

    www.ti.com/.../slua790.pdf


    thanks
    Onyx
  • 0 in reply to Onyx Ahiakwo
    Intellectual 310 points

    The three questions are separate. I'll try and clarify.

    Question #1 - I've attached a new file, "FuelGaugeConnection-201708161805.pdf", which shows that the way I want to connect things does not change the polarity.

    FuelGaugeConnection-201708161805.pdf

    Question #2 - I messed up and made with board with the opposite connection of what I showed in Question #1. So I still have the question, is it possible to reverse the polarity in software by configuring the chip differently?

    Question #3 - I can't find any reference to firmware updates for this device. I see that with the EVM one can program flash memory, which I would call configuration or parameter data, not firmware.

  • 0 in reply to hwswdesign
    Expert 2475 points
    You can connect the circuit as shown in your document. There is a GNDSEL bit in the Pack Configuration register to select the side of the sense resistor for the gauge ground connection. Your load, or charger, will be connected from "SYSTEM POWER" to ground. Also, note that the ground connection for the BAT voltage sense is on the load side of the sense resistor, so this may introduce some error in the voltage measurement due to the voltage drop across the sense resistor. It should be insignificant. Also note that this a simplified schematic and there are some capacitors missing. e.g. on REGIN and REG25.
  • 0 in reply to TEC
    Expert 2475 points
    I neglected questions 2 and 3. SRP must always be connected to BAT- or it will cause gauging issues. You can update the firmware on the device by programming a new srec file using the Programming screen, but there have not been any firmware updates to the bq34z100-G1. You can also use this screen if you have created a golden srec and want to program it to a new device.
  • 0 in reply to TEC
    Intellectual 310 points

    Thank you.

    My customer is using a battery pack that goes from 20V-29.2V. Are you saying that the sense voltage (+/- 120mV worst case) will be the error, at 20V there will be a voltage error of ~0.6% (0.12 out of 20)?

    Is this is best TI device for my application (20V-29.2V, 30 amps max, 5 amps average)?

    Regarding programming: So if I get the EV2300 EVM and connect it to my board's SCL/SDA pins, and then I can use your "bq34z100-G1 Battery Management Studio software"? That sounds great!!!

  • 0 in reply to hwswdesign
    Expert 2475 points
    Yes, the error will be present, but insignificant. The bq34z100-G1 should be a good fit for your application. You can use bqStudio to program the device over the I2C interface.