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BQ76940: ABLE TO BOOT THE DEVICE; ABLE TO SET OV_TRIP AND UV_TRIP VALUES; ABLE TO SET PROTECT2 CONTROL REG WITH 0X02; BUT NOT ABLE TO OBSERVE 12V @ DISCHARGE PIN

mohd imran khan
Intellectual 510 points
Part Number: BQ76940

Hi WM,

I am using BQ76940 with PIC 32MX575f512l for BMS.

I am able to boot the AFE and able to receive CAP3, CAP2 and CAP1 volt>3v.

I tried readying the STAT register and able to receive 0x04 as value.

Next step i Cleared STAT register by writing 0x04 to it and when i read STAT register was 0x00.

Now I loaded Protect2 register with 0x02 to make Discharge pin high.

Protect 2 register value was 0x02 but voltage at discharge pin was 0.

Can you suggest any corrective action for this!

Thanks

Imran

  • 0
    TI__Guru 54715 points
    Hi Imran,
    Status 0x04 is OV. You can clear OV , but if the condition is still present it will re-assert after the OV delay time. OV does not prevent DSG from being high though.
    UV would prevent DSG from going or staying high, but that would be status 0x08.
    You mention setting Protect 2 register to make Discharge high, but you need to set the DSG bit in SYS_CTRL2, address 0x05: bit 1, value 0x02.
    It may take some time to work through the conditions. Clear the faults in the status register, if they come back find and fix the cause of the faults. When the faults stay away after clear, write the SYS_CTRL2 bits 1 and 0 to turn on DSG and CHG as desired.
  • 0 in reply to WM5295
    Intellectual 510 points

    hi WM,

    My IC CAP1-vss got shorted due to high voltage appearing across REGSCR.

    I replaced the IC with good IC.

    After Replacing IC, i gave 3volts to TS1 to boot the IC.

    I am able to get CAP1-Vss, CAP2-VC5x, CAP3-VC10x voltages as 3.2v, 3.1v and 3.2v.

    But i am not able to get REGOUT volt. i am getting 230 mV across REGOUT pin.

    Can you suggest any input to rectify this error.

    Thanks

    imran

  • 0 in reply to mohd imran khan
    Intellectual 510 points
    hi WM,

    i checked across output capacitor there is no short at the output.

    across alert pin i am getting 200 mV .

    i checked there is no short across alert pin too.
  • 0 in reply to mohd imran khan
    Intellectual 510 points
    Hi WM,

    My source follower circuit is damaged.
    Mosfet in source follower got shorted.
    I removed the faulty mosfet and Directly gave 18.8v to REGSCR from cell 5th cell.
    When i give boot signal to TS1 pin, I am able to get CAP1,CAP2,CAP3 voltages to be 3.2v.
    But i am not able to get REGOUT and AFE is not Communicating.
    I am expecting there is some issue with REGSCR circuit.

    Can you suggest any input on this.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    There is no mode where CAP1 is on but REGOUT is off. Suggestions would be:
    Check that REGOUT is not shorted. You have done this.
    Check that REGOUT is not overloaded. Did you measure the current required and is it in range of the output?
    Check that REGSRC is present and in the right range.
    Check that pins are soldered to the board (REGSRC, REGOUT, VSS). VSS is likely connected or CAP1 would be bad. Be sure voltage is on both the pin and the board net.
    If the connections are correct, the new part may have been damaged by the bad source follower, depending on the voltage.
  • 0 in reply to WM5295
    Intellectual 510 points
    Hi WM,
    Thanks for your reply.
    There is no load connected to REGOUT pin.
    REGSRC is present and it is in the range of 11.3 to 13 v.
    When boot signal is not given regsrc volt is 13v and when boot is given its voltage is 11.3v.
    I resoldered the pins to confirm the connectivity i checked with multimeter for continuity and it is there.
    Still regout pin to vss is 300mV.
    Not able to figure out what is wrong with the IC.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points

    Hi Imran,
    It sounds like you have checked all connections. If there is no short the part must have been damaged somehow in handling, installation, or test.  You might check with a colleague to see if they can identify something different.

  • 0 in reply to WM5295
    Intellectual 510 points
    Hi WM,
    I replaced the IC with new IC and it started working and when boot signal is given to TS1 REGOUT, cap1, cap2 and cap3 voltages are coming and they are matching the spec values.
    But i am able to see some strange behavior of cap3, cap2 voltages.
    When i make connection as per table 8.3 even before giving boot signals i am able to observe CAP3-VC10x =3.2v,
    CAP2-VC5x = 3.2v and CAP1-vss = 0v, REGOUT = 0v.
    Once after giving Boot signal i am able to observe CAP1-vss = 3.2v, REGOUT _Vss =2.6v.
    And other cap voltages are same.
    As per datasheet when i give boot signal then only all cap voltages should appear along with regout. but here without giving boot i am able to observe cap3, cap2 voltages. what can be the reason for this?

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    If you get a transient on TS2 or TS3 during connection that group and the above group (if present) may power up. Be sure to have the thermistors or substitute resistors attached during board test.
  • 0 in reply to WM5295
    Intellectual 510 points
    Hi WM,
    I have substituted 10k resistors instead of thermistors.
    I am not sure of transients. i need to confirm this.
    But operation of AFE will not get effected due this right?
    I will confirm this too with microcontroller and i2c.

    Thanks
    Imran
  • 0 in reply to mohd imran khan
    Intellectual 510 points
    Hi WM,
    I am able to receive all the voltages from AFE.
    Thanks
    Imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    If the upper group wakes up first from some transient on its TS2 or TS3 line the part will likely show an XREADY fault when the part is booted. The MCU can clear that fault and proceed. Clearing faults should be part of normal operation.
  • 0 in reply to WM5295
    Intellectual 510 points
    hi WM,
    part is working fine.
    Thanks
    imran
  • 0 in reply to mohd imran khan
    TI__Guru 54715 points
    Hi Imran,
    It should work.