• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 527 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ76952: I2C failure while probing

Shyama Agrawal
Intellectual 860 points
Part Number: BQ76952

Hello,

We are facing problem with I2C when number of cells is reduce on the board. The pullup resistor is 2k. I2C is working fine with both 16s, 11s cell configuration. In 16s, we could also probe the signal. In 11s, when we probe the signal (SDA) the I2C is failing, if we probe (SCL), there is no issue. There is only 1 master (controller), 1 slave (BQ76952) both on the same PCB.

Please suggest what might be happening.

Edit: There is another offboard slave. The communication is through normal independent wires to the offboard slave. The communication doesn't fail while probing when 2 slaves and master are connected. It fails while probing when the offboard slave is deliberately disconnected.

PS: Please suggest a suitable wiring structure for an offboard slave

  • 0
    TI__Mastermind 42060 points

    Hello Shyama,

    Does the communication fail when disconnecting the offboard slave without the probes? Does this happen in both the 16s and 11s cell configurations? The probes/cell configuration should be causing any issues with the I2C signal.

    Depending on how long the communication wires are, you may need an I2C Buffer or circuit filtering. Have you tried sending 9 clock signals through the I2C after disconnecting the offboard slave? It could be possible that disconnecting it caused a glitch in the BQ76952 to see a false clock edge. Sending the 9 clocks would free-up the I2C bus.

    Could you also post a diagram of the components of your board to off-board set-up?

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Intellectual 860 points

    Hello Luis,

    Thank you for your message. We have reduced the I2C bus speed to 200kHz and now it is working fine. We are using a shielded 4 core 20cm cable (Not a twisted pair cable) to connect to the off-board slave. Do you recommend using the same or shifting to a ribbon cable? We are worried about external EMI since the application is automotive. 

    PS: Shield of the cable is connected to ground on the off-board slave side.

  • +1 in reply to Shyama Agrawal
    TI__Mastermind 42060 points

    Hello Shyama,

    Definitely keep the shielded cable. I am glad it is now working fine, I2C is usually used for on-board or short distance communication, so for longer distances a shielded cable, buffer, or other circuitry might be need it so that the signal does not hang. Lowering the I2C bus speed is also an option I've seen, so I am glad this was enough to get things working.

    In case it stops working again, try sending 9 clock signals to the IC, this should free up the I2C bus line.

    Best Regards,

    Luis Hernandez Salomon