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bq78350 communication error

Girish Gangadharaiah21
Prodigy 10 points
Other Parts Discussed in Thread: EV2400, BQ78350
We are experiencing SMBus Communication problems while connecting our BMS board to the Battery Management Studio GUI. When I try to use the scan tool in the GUI , the connection is not consistent and throws up these errors :

  • No acknowledge from device.
  • Timeout or unexpected response communicating with device.
  • Timeout or device is busy.
  • Packet checksum mismatch.

The register values are getting updated but, there is a loss in communication in between while using the scan tool. This doesn't happen while reading single registers using Advanced Comm SMB.

Can anyone help us finding why is this happening

  • 0
    Intellectual 295 points
    This sounds like the data transmitted over the SMBus is getting corrupted due to signal integrity problems.
    Here are some things to check:

    Are you using the EVM?
    If so, check that all the correct jumpers are installed on the board. Follow the instructions for the Gauge quick start.

    If it's not the EVM, are you controlling the BMS with an external microcontroller or IC?
    If that's the case, are you trying to listen to the line while a microcontroller or IC is also present on the bus? Two devices on the bus might cause problems if proper termination is not included. Try disconnecting the SMBus from the microcontroller or IC and check if the BQ studio is getting all messages.

    (EVM only): What about the AFE communication? Does it work properly if you follow the AFE Quick start guide? If not, you might have an interface board problem, supply problems, ground problems.

    Which interface board are you using, EV2300, EV2400?
    Check whether the proper jumpers are installed on the pull-ups SCL, SDA, REGOUT, ALERT. (Check the instuctions to make sure which ones).

    Check the signal on the using an oscilloscope to see whether there is a lot of noise on the clock or data line. (you can compare with the EVM)
    With short transmissions, you will not see any problems, however, with longer messages, problems might occur.

    I hope this helps you guide your troubleshooting.
  • 0 in reply to Michal Solecki
    TI__Guru 54715 points

    Excellent suggestions.  

    The I2C may seem unrelated to SMBus, but communication to the AFE is a high priority for the bq78350 and will take priority over the SMBus activity.  As noted above, be sure there is good connection, pull ups present and no bus collisions.  The I2C lines should show a burst of activity each 250ms with quiet time between.  If traffic is continuous something is wrong.

    Of course check the SMB cable for lose or broken wires or contamination.