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BQ76952: Advice on Battery Monitoring IC for 4S LiFePO4 with Open-Wire Detection and Removable Cells

Max Keller
Prodigy 25 points
Part Number: BQ76952
Other Parts Discussed in Thread: OPA4197

Tool/software:

Hi,

I’m seeking advice on selecting the appropriate battery monitoring IC for a project involving a 4S LiFePO4 battery pack. My key requirements are:

  1. Accurate Cell Voltage Monitoring: I need to measure individual cell voltages in a series-connected pack.

  2. Open-Wire Detection: The system should reliably detect when a cell is physically disconnected (i.e., reading 0V or open-circuit conditions).

  3. Handling Removed Cells: The IC should continue monitoring the remaining cells accurately, even if one or more cells are removed from the stack.

  4. External MCU Integration: I’ll interface the monitoring system with an external microcontroller via I2C or SPI.

I initially considered using precision rail-to-rail op-amps (like the OPA4197) configured as differential amplifiers to measure cell voltages. However, handling floating inputs when cells are removed has proven to be a non-trivial design challenge. To simplify the design, I’m considering dedicated battery monitoring ICs for voltage readings and open-wire detection, with the BQ76952 as a potential candidate.

That said, I’m concerned about the BQ76952’s open-wire detection capabilities. From what I understand:

  • The IC doesn’t provide a dedicated register for tracking which cell is disconnected.
  • It supports detecting only one open-wire event at a time.
  • In the case of an open wire, the IC may trigger overvoltage protection for the cell above and undervoltage protection for the cell below. However, this indirect detection method may not satisfy my requirement to explicitly identify multiple disconnected cells while still monitoring the remaining ones accurately.

I'm unsure if I should continue with my op-amp setup or shift to a dedicated battery monitoring IC.

Would you recommend any specific TI products that can meet these requirements? Additionally, any insights on configuring the ICs to handle open-wire detection and removable cells would be greatly appreciated.

Thanks.

  • 0
    TI__Genius 17945 points

    Hello Max,

    Max Keller said:
    The IC doesn’t provide a dedicated register for tracking which cell is disconnected.

    Correct.

    Max Keller said:
    It supports detecting only one open-wire event at a time.

    Our part supports detecting more than one open-wire event at a time, however, it would be through the cell above triggering OV and the cell below triggering UV.

    Max Keller said:
    I'm unsure if I should continue with my op-amp setup or shift to a dedicated battery monitoring IC

    The BQ76952 seems to be a better fit for what you are looking for despite there not being a dedicated OW register. I am unable to say if the OPA4197 would be better suited to this as you mentioned the difficulty of the design challenge as well it is a different team’s part. If you want to inquire more about the OPA4197, I recommend opening a new forum post for the part inquiring for advice from their perspective.  

    Max Keller said:
    Would you recommend any specific TI products that can meet these requirements?

    Our monitors to my knowledge do not offer any specific register for tracking open wire and instead use the similar method as mentioned above. 

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 25 points

    Hi Alexis,

    Thanks for your reply. As long as we can determine which cells are disconnected, that is sufficient.

    So to confirm, does this mean that one adjacent cell is going to go towards under-voltage while the other adjacent cell is going toward over-voltage. So the voltage readings of the adjacent cells will be incorrect until the cell is re-connected?

    Thanks

  • 0 in reply to Max Keller
    TI__Genius 17945 points

    Hello Max,

    Max Keller said:
    So to confirm, does this mean that one adjacent cell is going to go towards under-voltage while the other adjacent cell is going toward over-voltage. So the voltage readings of the adjacent cells will be incorrect until the cell is re-connected?

    Correct. To be more specific, the adjacent top cell shows up as overvoltage, and the bottom adjacent cell shows up as undervoltage. 

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 25 points

    Thanks Alexis,

    This answers my question.

    It would be preferable to be able to measure the voltages of adjacent cells accurately even whilst a cell is disconnected. Do you by chance know of any product capable of this?

  • 0 in reply to Max Keller
    TI__Genius 17945 points

    Hello Max,

    I'm glad that answered your question.

    Max Keller said:
    It would be preferable to be able to measure the voltages of adjacent cells accurately even whilst a cell is disconnected. Do you by chance know of any product capable of this?

    Most, if not all, of our battery cell monitors work this way for open wire. You can try opening a new forum and asking the gauges team to see if they have something that would work more to what you desire.

    Best Regards,
    Alexis