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BQ76952: Manufacturing Process w/OTP

Don Schelle
Expert 4150 points
Part Number: BQ76952
Other Parts Discussed in Thread: EV2400, BQSTUDIO

What would normally be the manufacturing process (when OTP programming is included)?

Since the OTP memory includes calibration, I expect that you’d need to connect the BQ76952 to the cells first to load all the values to the registers. To write to OTP, you’d need to disconnect the cells and plug in an 10-12V supply. But when you disconnect the cells the BQ76952 loses power, so you lose your register values. Would you just need to export the export the config, and then just re-load it afterwards to do an OTP write? Is the 10-12V supply applied at the cell inputs or is there usually a BAT connector for this purpose? The process seems awkward and I feel like I’m missing something.

  • 0
    TI__Guru* 81034 points

    Hi Don,

    OTP programming would either need different production hardware, or a way to apply 10-12V to your board for the programming step before the cells are connected. We recommend programming OTP if there is a need for the REG1/REG2 regulators to be powered at startup or if you need to change the communication mode for the device. If the default settings are okay (there are different pre-configured part numbers for these parameters like BQ7695201, BQ7695202, etc), then you can just load your register settings from the microcontroller at startup. I think most users are doing this. You can see the example microcontroller code available in the BQ76952 product page to see how to do this.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 90 points

    Hi Matt,

    Don's question is related to an email discussion we had recently. I have a few additional questions.

    If 10–12V is applied to BAT for communicating with the BQ76952 over I2C and writing to OTP memory, do you still need to meet the requirement that VC0, VC1, VC2, VC15, and VC16 be connected to cells? Or would it be acceptable to simply have a test point (or connector) on BAT, VSS, SDA, and SCL and use these only? I’d much prefer to just leave the cell inputs floating (including VC16). I imagine that's OK since the BQ76952 has open-wire detection and I don't expect that the whole chip would stop working if the cell taps got disconnected. Note that I plan on having a separate connection for BATT+ and VC16. 

    Can you also confirm that the EV2400 provides the pull-ups for the I2C bus? I see that there are pullups on the EV2400 schematic, but there are transistors to turn them on/off. Although the user guide does say it’s pulled up. I was thinking of having the pull-ups to REG1; are there any problems with that?

    And is bqStudio able to work with and without CRC enabled?

    And a slightly unrelated question, how important is it that unused cells be shorted? What would be the harm in letting a cell input float? If you wanted to design a flexible BMS board and wanted to avoid assembly variants, could you just leave them floating at the connector and just have the configuration be different? Given that the BQ76952 has the internal balancing FETs, it seems like a missed opportunity to not just provide the ability to have those be always enabled when the cells are marked as unused.

    Thanks,

    Alex

  • 0 in reply to Alex LeBlanc
    TI__Guru* 81034 points

    Hi Alexandre,

    Yes, it is best not to be connected to cells while programming the OTP. I think you may also need to connect to VC16 along with BAT, VSS, SDA, SCL. 

    EV2400 has internal I2C pull-ups to 3.3V. In the application, pullups to REG1 are good as long as REG1 is enabled in OTP. 

    BQStudio will work with and without CRC enabled. If you change the Comm Mode, it is good to restart BQStudio so it can detect the new mode.

    I do not advise letting the inputs float. Unused cells should be shorted. The device reports the voltages difference measured between VCx pins, so leaving pins floating will not work. The internal balancing FETs do have a small resistance so this would not be a good method to short cell inputs. 

    Best regards,

    Matt