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BQ78350: BQ78350 - Can't communicate through SMB

Part Number: BQ78350

Hello everyone,

I am using a BQ78350 with a BQ769300. When using the EVM I was able to communicate successfully with BQSTUDIO, however when I used my PCB, I wasn't able to communicate with the BQ78350. I tried with both EV2400 and EV2300, but both attempts were unsuccessfull. The SMB lines are connected to the BQ78350 only, although I have an internal MCU in the layout, I did not place it to test the BQ78350 communication line alone. I have the feeling that the system is actually working since I can see in the oscilloscope the pulses from the VEN pin. I measured the SMC signal and it looks like this:

Do you have an idea of what could be happening?

Thank you very much!

  • Hi Luis,
    If the MCU does not talk to the bq78350 I would suggest checking the addressing from the MCU to the bq78350.
    If the EV2300 or EV2400 won't talk to the bq78350 and the signaling looks ok, check the connections to be sure they go to the proper pins. Make sure the MCU is not interfering with the communication. Also look at the I2C lines to the bq769x0. The bq78350 relies on the bq769x0 for data for its operations, if it can't talk to the monitor device it will spend its timeline trying to talk to the monitor and may not respond to SMBus.
    Probe the I2C lines, if they have short bursts of traffic every 250 ms it may be communicating well. If the bus is continuously busy that is likely the problem, correct the I2C before attempting to resolve the SMBus.

  • Hi Luis,

    This looks strange. If the AFE is successfully communicating with the Gas Gauge you should check the ALERT to see if the device detected a fault and is protecting it self. The BQ could be on sleep state. Just make sure the host connection is successfully perceived.

      This might not be the issue but it is worth testing. Also to check correct operation you can enable the Display pin and read the voltages on the leds pins. 

  • In reply to WM5295:

    Thank you for the reply, I checked the communication lines between ICs and fixed the problem.

    Have a great day!

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