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BQ4050: LED Display, Auto Start of FETs, SMB Bus connection

Fabian Luttenberger
Prodigy 235 points
Part Number: BQ4050
Other Parts Discussed in Thread: BQ25703A, , EV2400, BQSTUDIO, BQ294502, BQ28Z610

I have a custom board with BQ4050 and BQ25703a and an EV2400 for development purpose. So far everything works as expected but I do have some minor issues/questions:

  1. I have the /DISP pin shortened to GND. Is it still possible to drive the LEDs to indicate SOC?
  2. I plan for a battery that is NR, and the NR bit is set. However, for development purposes I can disconnect the battery over a connector to power the system off. Whenever I connect the battery to the system, the FETs won't turn on, I have to frist put in the power adapter and then the FETs turn on. Is there a way to turn on FETs automatically when BQ4050 detects a battery? Note: PRES is permanently connected to GND.
  3. I can read the BQ4050 registers with ESP32. However, after a couple of minutes I cannot read certain values (e.g. cell voltages) anymore, althought some value are still readable (e.g. SOC). Any ideas on this issue?

  • 0
    TI__Guru 52115 points

    See my answers below.

    I have the /DISP pin shortened to GND. Is it still possible to drive the LEDs to indicate SOC?
    [Andy]No. As you see in the TRM, the bq4050 device has an LED display that shows various status information when a high-to-low transition of the DISP pin is detected.

    I plan for a battery that is NR, and the NR bit is set. However, for development purposes I can disconnect the battery over a connector to power the system off. Whenever I connect the battery to the system, the FETs won't turn on, I have to frist put in the power adapter and then the FETs turn on. Is there a way to turn on FETs automatically when BQ4050 detects a battery? Note: PRES is permanently connected to GND.
    [Andy] No. The gauge assumes it works in the NON-REMOVABLE mode since the NR bit has been set.

    I can read the BQ4050 registers with ESP32. However, after a couple of minutes I cannot read certain values (e.g. cell voltages) anymore, althought some value are still readable (e.g. SOC). Any ideas on this issue?
    [Andy]Try bqStudio and see if you can see the same problem.

  • 0 in reply to Andy Liu (BMS)
    Prodigy 235 points

    Thank you.

    I would have another 2 question:

    1. When is a secondary cell voltage monitor (e.g. bq294502) necessary in addition to bq4050 and bq25703a? Is there any further reading available on this topic? 
    2. It seems like bq28z610 would be a suitable replacement for my application, as it has a lower external component count and I only have a 2s config. Would this be an appropriate replacement? Are there any drawbacks (e.g. more effort to calibrate or set up)?

  • 0 in reply to Fabian Luttenberger
    TI__Guru 52115 points

    See my comments below.

    1)  See this thread https://e2e.ti.com/support/power-management/f/196/t/616636.

    2)  BQ4050 a CEDV based gauge while BQ28z610 is an Impedance Track gauge.  Normally,  bq28z610 is able to provide more accurate SoC prediction.  In addition, bq28z610 needs a correct chemistry id to work properly and also a learning cycle needs to be done.  

    Andy