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BQ34Z100-R2: Battery Protection and Fuel Gauge Review Request (BQ34z100-R2 with BQ7790522PWR)

Al M
Prodigy 70 points
Part Number: BQ34Z100-R2
Other Parts Discussed in Thread: BQ34Z100, EV2400, BQ41Z90, PMP23329

Tool/software:

Hi all,

We would like to protect a 9S LiPo battery pack and add a fuel gauge feature.

For protection, we are using the BQ7790522PWR with MOSFETs, everything is rated for 50A max. We’ve added a fuel gauge stage using the BQ34Z100-R2 to monitor the remaining capacity of the pack.

Could you please review the schematic and let us know if you notice any potential issues?
Our main concerns are:

  • Can we use the same shunt resistor for both ICs?

  • We plan to use the EV2400 to program the BQ34Z100, and then communicate over I2C with our C2000 microcontroller. Since the BQ7790522 cuts power on the low side, this means the microcontroller won’t share a ground with the BQ34Z100 during cutoff. We’ve added an I2C isolator — could you confirm whether we can power the isolator from REGIN, or should we generate a separate 5V_ISO rail?

  • If you are aware of a single IC that combines both protection and fuel gauge functionality for 9S LiPo packs, we’d love to hear about it.

  • If the circuit remains connected while the battery is in storage, could it cause unwanted current draw and slowly drain the pack? Should we add a switch or another method to fully disconnect it?

Thank you,
BatteryProtector_FuelGauge.pdf

  • 0
    TI__Mastermind 31740 points

    Hello AI,

    We have assigned this trend and will be reviewing your question.

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    TI__Mastermind 31740 points

    Hello AI,

    Al M said:
    Can we use the same shunt resistor for both ICs?

    -We recommend using separate shunt resistor for the two ICs.

    Al M said:
    We plan to use the EV2400 to program the BQ34Z100, and then communicate over I2C with our C2000 microcontroller. Since the BQ7790522 cuts power on the low side, this means the microcontroller won’t share a ground with the BQ34Z100 during cutoff. We’ve added an I2C isolator — could you confirm whether we can power the isolator from REGIN, or should we generate a separate 5V_ISO rail?

    -The battery gauge ground shouldn't be getting cutoff due to the fets being turned off and on. The battery gauge should always be connected to the cell's pwr and gnd of the cell.

    Al M said:
    If you are aware of a single IC that combines both protection and fuel gauge functionality for 9S LiPo packs, we’d love to hear about it.

    Currently the best option would be the bq34z100 however there is a new battery gauge pre-RTM named BQ41z90 that has the ability to control the fets and to do 9s.

    BQ41z90:
    https://www.ti.com/product/BQ41Z90

    Al M said:
    If the circuit remains connected while the battery is in storage, could it cause unwanted current draw and slowly drain the pack? Should we add a switch or another method to fully disconnect it?

    -There is a current drain on the battery gauge end however we don't typically recommend to add a switch 

    Thank you,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 70 points

    Thank you Alan  for your support,
    You are right, the battery gauge ground won't be getting cutoff due to the fets being turned off and on but the I2C communication will, because the microcontroller because it is after the fets. Do you think we need the 5V isolated or we can use the REGIN to power the isolator?

    The BQ41z90 does seem perfect. Do you know when it will be available, or if samples for prototyping are already accessible?

    Best,

  • 0 in reply to Al M
    TI__Mastermind 31740 points

    Hello AI, 

    Al M said:
    You are right, the battery gauge ground won't be getting cutoff due to the fets being turned off and on but the I2C communication will, because the microcontroller because it is after the fets. Do you think we need the 5V isolated or we can use the REGIN to power the isolator?

    I would look into this reference design that uses the BQ34z100 and BQ7721600PW.

    PMP23329:
    https://www.ti.com/tool/PMP23329

    Al M said:

    The BQ41z90 does seem perfect. Do you know when it will be available, or if samples for prototyping are already accessible?

    -There has not been an official date for the IC release and I would reach out to your local TI sale rep but EVM's are available for purchase 

    EVM:
    https://www.ti.com/product/BQ41Z90

    Thank you,
    Alan