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Original question:

BQ78350-R1A: bqStudio No Acknowledge From Device

BQ78350-R1A: No acknowledge from eval board to EV2400

Greg Decker
Prodigy 225 points
Part Number: BQ78350-R1A
Other Parts Discussed in Thread: BQ78350-R1, EV2400, BQSTUDIO, , BQ78350, BQ76930

I have a BQ78350-R1 evaluation board that I have configured for 7 series cells. I had 7 cells running a discharge log over night. When I got in, the cells had discharged to below 1V and the BQ software had locked. I forced it to quit and removed the dead cells, replacing them with a fresh pack of cells, but now the BQ software will not acknowledge that there is a powered board connected. The board boots as expected (the discharge FET turns on when TC1 is pulled low by pressing the boot button, and i'm getting 2.5V at Vreg out.( The charge FET won't turn on, however-- not sure if that's relevant)

I've also tried using a power supply instead of cells. Same result: No acknowledge from the device.

I've tried the EV2400 and eval board  on a different computer, same result.

I've tried resetting the EV2400, same result.

I don't think the eval board is bad-- the voltages that should be present appear to be present. Is there a way to check to see if the EV2400 is dead? Am I missing something with the eval board?

  • 0
    Prodigy 225 points

    As an update, I have checked the following nodes:

    Input voltage on J1, J2 is 26.7V but I see the same behavior up to 29.4V.

    1) SCL, SDA pull ups on J14 are 2.5V and jumper in in place.

    2) Regout on J14 is 2.5V and jumper is in place

    3) CAP1 is 3.289V, CAP2 is 18.67V, CAP3 is 0V

    4) DSG measures 12.37V

    5) CHG measures 0V

    6) PRECHG is 2.044V

    7) GGpower is 2.5V

    8) VC5X is 15.49V. VC10X is 27.01V

    9) TS1 is 0V unless I press the boot button, when it is 2.93V until I release it. TS2 is 15.4V, TS3 is 0V

    10) REGSRC is 13.17V

    11) SAFE and ALERT are both 0V

    I get an indicator in the upper left part of the BQStudio window indicating that I have an EV2400, revision 0.18, so the EV2400 appears to be functioning.

  • 0
    Prodigy 225 points

    Additional information on the eval board: Pin 2 on J16 measures 1Mohm to ground, but pin 3 measures 22ohms to ground (no ev2400 connected)

    I think my SMBD pin might be damaged on the eval board.

  • 0 in reply to Greg Decker
    TI__Guru* 81034 points

    Hi Greg,

    Thanks for sharing the additional data. The indicator in the upper left part of BQStudio showing the EV2400 rev 0.18 is a good sign the EV2400 is functioning. If the BQ78350-R1A is not being highlighted on the Dashboard, it means the EV2400 is not communicating with the BQ78350 for some reason. It looks like your measurements on the nodes you listed look good. If there is damage on the SMBD pin of the BQ78350, that may explain why this communication is broken. Do you have another device you could replace it with on the board?

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 225 points

    EDIT:

    I removed D54 but the low resistance path to ground remained. I believe the issue is the BQ78350, pin 11.

    I'm looking into ordering a new BQ78350-R1 and a replacement eval board.

  • 0 in reply to Matt Sunna
    Prodigy 225 points

    Do you have any insight into why the SMB data line on the BQ78350-R1 may have failed? I know the cells overdischarged while I had the BQstudio software trying to log, but it seems to me the fuel gauge should be able to handle something like that.

  • 0 in reply to Greg Decker
    TI__Guru* 81034 points

    Hi Greg,

    I agree that the over-discharge should not have caused the SMBD pin to fail. It seems there must be something else at play. The device would likely have gone into a voltage-based Shutdown (the BQ76930 will turn off the REGOUT supply to the BQ78350), so the BQ78350 would be powered off. I think the EV2400 has an internal 3.3V pull-up rail for the SMBus lines. The EVM jumpers you mentioned are in place which connect the SMBus pullups on the EVM to REGOUT. Maybe if BQStudio is exercising the SMBus lines while the power to the BQ78350 is off, it could cause an issue.

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 225 points

    Absolute Max for IO pins (according to the datasheet) is VCC+0.3. If VCC dropped below 0.3V, that could potentially blow the line.

    VCC shouldn't have dropped that low. It was a 7S pack, and the average cell voltage was 0.5V. It also doesn't explain why SMBD failed but not SMBC.

  • 0 in reply to Greg Decker
    TI__Guru* 81034 points

    VCC would drop to 0V if the REGOUT turns off. By default, the device will go into Voltage-based Shutdown if any of the cell voltages falls below 1750 mV.

  • 0 in reply to Matt Sunna
    Prodigy 225 points

    How do I keep the SMB pins from becoming damaged in the event of a voltage-based shutdown?

  • +1 in reply to Greg Decker
    TI__Guru* 81034 points

    Hi Greg,

    In the application the SMBus pullup resistors will normally be connected to REGOUT. This will go to 0V when the part goes into Shutdown.

    You could maybe remove the pull-up resistors on the EV2400 and use the EVM pull-ups to REGOUT instead. This should prevent unwanted voltages on the SBM pins.

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 225 points

    Such a simple solution! I regret not thinking of it.