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BQ78350-R1: Approaches to using custom balancing algorithm when using the BQ78350-R1? Can I individually control the AFE balance FETs directly via the BQ78350-R1?

Senthil Seveelavanan18
Prodigy 160 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQ76930, BQ34Z100-G1, BQ34110, BQ76940, TIDA-010030

1. Can I individually control the AFE balance FETs directly via the BQ78350-R1?

2. If not, is the next best option to use a MCU share the I2C bus with the BQ78350-R1, and implement my own custom balancing algorithm?

3. What other approaches are there for using a custom balancing algorithm when using the BQ78350-R1?

I want to balance whilst idle in addition to when charging

Many thanks

  • 0
    TI__Guru 54715 points
    Hi Senthil,
    1. The bq78350-R1 does not support direct control of the AFE balance FETs.
    2. The bq78350-R1 does not expect to share the bus with another host. It does not negotiate for the bus and collisions may occur. If there are errors in communication the bq78350 will go into a recovery mode and spend most time trying to communicate with the AFE since that is vital to its operation. Also the bq78350-R1 will periodically check register values and correct any it finds that differ from its settings.
    3. The bq78350-R1 does not have a balance during rest option or provide for custom balancing algorithms. The test commands are not available when sealed and don't have the desired function. Manufacturing access command 0x59 AFE Config is a read only command, 0x1B Cell Balance Toggle does not allow bit control.
  • 0 in reply to WM5295
    Prodigy 160 points

    thanks very clear but... yikes!

    any approach you can recommend for me to be able to achieve my goals, without ditching the BQ78350-R1?

    any thoughts on this idea:

    manually use a MUX to hand over control to a MCU after X_seconds of a known 'rest session'.  Where X_seconds is enough time for the battery to settle and the BQ78350-R1 enough time to do its thing??

  • 0 in reply to Senthil Seveelavanan18
    TI__Guru 54715 points
    Hi Senthil,
    The bus is left idle when the bq78350 is not talking, so a mux is not necessary to allow bus operation. If the bq78350 is switched from the bq769x0 it will still be upset and go into recovery mode when it can't find the monitor device. Current consumption will increase, gauging information may be lost (although you are considering rest), and it could generate a permanent fail.
    When the bq78350-R1 is in sleep mode the transactions slow to the times set in the sleep configuration. This leaves more time between bq78350-R1 transactions to talk to the AFE. It won't change the gauge behavior if it can't find the AFE or finds registers changed. I still would not recommend it. Your time is likely better spent designing the function you want in your MCU than working around a fixed behavior with uncertain results.
  • 0 in reply to WM5295
    Prodigy 160 points

    ok thank you for this clear info.

    Are there any other TI gauging ICs suitable for 10 series cells (BQ76930)?

    My motivation for the BQ78350 is to have accurate state of charge estimation without having to implement complicated algorithms myself. I'm happy to manage the AFE myself

    edit: I have created a new question on the forum..

  • 0 in reply to Senthil Seveelavanan18
    TI__Guru 54715 points
    Hi Senthil,
    The TIDA-010030 shows a BQ76940 for monitoring and controlling balance of the cells under control of a MCU while fuel gauging is provided by a BQ34z100-G1. For 10 cells a BQ76930 could be used. As an alternative for the gauge the BQ34110 has CEDV gauging similar to BQ78350-R1. I did not think of this earlier. This approach provides the state of charge from the gauge while allowing flexibility of/for your balance algorithm. It does require you to implement temperature protections in the MCU as wall as setup & recovery from faults in the BQ76930 and implementation of any customized or flexible protections.
  • 0 in reply to WM5295
    Prodigy 160 points

    Great news,

    So in summary, the BQ769x0 (BQ76930 in my case) will work with the following TI gauges. Which unlike the BQ78350, aren't 'controllers', so require/enable custom management including custom balancing. Perfect.

    • BQ34z100-G1
      • impedance track algorithm
      • there is a reference design TIDA-010030
    • BQ34110
      • CEDV algorithm
      • no reference design?

  • 0 in reply to Senthil Seveelavanan18
    TI__Guru 54715 points
    Hi Senthil,
    Yes.