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BQ40z60 - OCD1 and OCD2 recovery

FB
Intellectual 350 points
Other Parts Discussed in Thread: BQ40Z60

Hi,

after a Over-current during Discharge (OCD) event the Safety Status low bit (OCD1 and/or OCD2) and XDSG is set.

Discharge is disabled - thats working fine.

The OCD recovery threshold is set to 200mA and 5s. The problem is to enable discharge after OCD event occurred. I have to send a reset command to reset OCD status. How can I set the BQ40z60 to automatic enable discharge after OCD event?

Best regards,

Fabian

  • 0
    TI__Guru 73830 points

    The CHG FET should not have turned off due to an OCD fault. The OCD Recovery threshold is a 200mA charge current. Does the DSG FET turn back on after you apply a charge current for at least 5s?

  • 0 in reply to ThomasCosby
    Intellectual 350 points
    the recovery threshold seems to be the problem. When I apply a charge current (after a OCD event), the charge LED blinks and the chip draws 70mA current.
    The OCD event is not reset. By reducing the threshold to 50mA (<70mA) OCD is reset. After 5s the chip draws 800mA wich is the correct charging current.

    As a fix I could reduce the threshold, but what could cause the problem with the low charge current? The charge current is set to 800mA.
  • 0 in reply to FB
    TI__Guru 73830 points
    Lowering the threshold should not cause a problem the charger or gauge. It is just the threshold where the gauge declares that charging has commenced and it switches over to charge mode.
  • 0 in reply to ThomasCosby
    Intellectual 350 points
    Some packs are working fine. I fixed the one mentioned above by setting the threshold to 50mA. Two other packs only draw 3mA when connecting a supply after ocd event. Also the LED is not blinking. When I set the threshold to 2mA (5s) it starts charging and blinking.

    I dont think that there is a hardware issue. Do you have any idea what could cause the problem?
  • 0 in reply to FB
    TI__Guru 73830 points

    Could the cell voltages be low enough for the charger to be on pre-charge mode? Are you using the TI EVM or your own design? If you can export an srec file, then I can try reproducing the problem to help work it. I will need to know the cell voltage conditions and how the SCD was induced.

  • 0 in reply to ThomasCosby
    Intellectual 350 points

    sorry for the delay, but I finally exported the attached srec file. The problem seems to occur in every state of charge. The charging current is set correct and not on pre-charge.  I am using a custom design but it is close to the EVM. OCD is triggered by applying a load > 2,8A.

    I hope you got all information to reproduce the problem. Any hint would be nice.

    BQ40z60_OCD_Problem.zip

  • 0 in reply to FB
    TI__Guru 73830 points

    Try setting the Minimum Output Voltage to 4220 and the Voltage Resolution to 16. I found this work for your setup.

  • 0 in reply to ThomasCosby
    Intellectual 350 points

    unfortunately I am facing the same problem in my newest design.

    In the technical reference manual on page 58 I can find a description how to calculate the "minimum voltage output" and "voltage resolution"

    Which value should R1 and R2 have?

  • 0 in reply to FB
    TI__Guru 73830 points
    These are the resistor values that we use on the EVM.
    4-s Cells,R1 = 332k, R2 = 26.1k
    3-s Cells,R1 = 332k, R2 35.63k
    2-s Cells,R1 = 332k, R2 = 56.13k