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BQ76930: General questions on device features

Theo Franquet
Prodigy 80 points
Part Number: BQ76930
Other Parts Discussed in Thread: BQ78PL114, BQ76200, BQ78350

Hi, 

I am looking into hardware solution for BMS development, offering the following functionalities:

- Coulomb counting for accurate gas gauging

- External MOSFET balancing triggering (for passive balancing)

- Temperature/Votage/Current monitoring

- Safety features reagrding over/undervoltage

The bq769x0 datasheet checks all those boxes it seems, but is there any other hardware necessary to achieve all this (spec sheet mentions a companion: what does it consist of, and to what extent does it fulfill the above functionalities?). 

Initially interested in TI's bq78PL114, but it is now labelled as Not Recommended for New Designs (NRND), is the bq769x0 the closest available hardware available for my application?

Thanks

  • 0
    TI__Expert 4640 points

    Hi Theo,

    The bq769x0 is the device you are looking for. The companion part refers to the bq78350 which is a gauge. You can use the companion part to manage the part or you can use an MCU but you will need one or the other. Additional you could consider the bq76200 for high Aide protection if you want your system (not the BMS system) to talk to the BMS system.

    Thanks

    Miguel

  • 0 in reply to Miguel Angel Rios
    Prodigy 80 points

    Hi Miguel,

    Thanks for your reply, I was also wondering if the hardware we are talking about here can be used for very high current applications (50+ Amps). What is the max continuous current measurable? 

    If it is unable to withstand such currents, would you recommend to use the same bq769x0 chip alongside a separate high current sense amplifier, if so, which one?

    Thanks

  • 0 in reply to Theo Franquet
    TI__Expert 6085 points

    Theo,

    referring to the d/s of the bq769x0, OCD thresholds are 100mV (when bit < RSNS=1>) and 50mV ( when bit<RSNS=0);

    Likewise SCD thresholds are 200mV and 100mV.

    By sizing the Rsense value, the bq769x0 can cover various ranges.  in this example for OCD,

    with a 1mOhm sense resistor, you should be able get a trip @100mV for 100A.

    with .5 milliohm, the current can be 200A. 

  • 0 in reply to Vish Nadarajah
    Prodigy 80 points
    Thanks very much for your clear answer.

    In the case where using say a .5milliOhm sense resistor, what would be the accuracy of the current sensor, the datasheet mentions +/- 10% for OCD/SCD scale accuracy, does it correspond to a current sensing accuracy of +/- 10% of the stack current?
    The reason I am asking is that discharge currents can reach very high amplitudes while CCCV charging will involve currents in the range of 10^-2A.

    Thanks,
    Theo
  • 0 in reply to Theo Franquet
    TI__Expert 6085 points

    Its the worst case of the trip point threshold of the OCD, SCD threshold across entire band of the temp and voltage operation. its a 6 sigma derivation.

    Hence the selection of the Rsense accuracy is also important. 

    This device is used in application in the 200-400A range with ease.

    SCD Threshold  = 200mV

     the CC accuracy 1 LSB 200mV/ ( 2^15 ) = 8.4uV

    hence there are 24K counts (i.e 200mV/8.4uV ~ 24K.

    32K-24K = 8K counts will be unused.

    thanks

    vish