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INA3221 - I2C Comms Issue

Raphael Mosig
Prodigy 140 points
Other Parts Discussed in Thread: INA3221

Hi,

I am using three INA3221 devices to measure currents and bus voltages. The schematic is shown here:

So, the the schematic is nothing special, all of them are connected to a single I2C master (a microcontroller). The addressing is done as shown below, IC8 has the address 0x41, IC9 has the address 0x40 and IC10 has the address 0x43 (according to the datasheet).


Now the problem. When I try to read register 0x01 from every device (with the identical function, apart from the device address), just IC9 sends useful information. After some investigation with the scope I can say, that something on the I2C lines is wrong, but I don't know what could cause such behavior.

Here are the measurements done with the scope on SCL and SDA when I try to read from register 0x01.

As you can see, just IC9 sends correctly, IC8 shows some weird I2C level errors and IC10 doesn't ACK to the address at all.

What could be the reason for the shown errors?
 Might it be possible, that an address conflict causes the weird levels measured in the IC8 graph?

Thanks in advance!

Best regards,

Raphael Mosig

  • 0
    TI__Expert 4595 points

    Hi Raphael,

    Let me look into this and get back to you.

     

     

  • 0
    TI__Mastermind 26485 points

    Hi Raphael,

    I have a few questions.

    1. Are the grounds of the I2C master (a microcontroller) the same ground as the "Secondary Ground".
    2. Are all INA3221 Grounds(GND pin3) connected to this same "Secondary Ground"
    3. At what speed are you communicating to the devices?
    4. Is there many devices connected to the I2C bus?

    Thanks,

    Javier

  • 0 in reply to Javier Contreras4
    Prodigy 140 points
    Hi Javier,
    thanks for your questions...they helped me a lot to find the issue.
    When I checked the second point, I found out, that there was a problem caused by my schematic and layout tool. In the schematic all the grounds (secondary ground) are connected properly (its not shown in my screenshot here)...at least it seemed so. But they were not connected to pin 3 of IC8 and IC10 although it looked like that. In the layout it was obvious that the pin 3 of two of the INA3221 are not connected to ground.

    After connecting pin 3 of the not working INA3221, everything is working as expected.

    Thanks for the help and the idea to find the reason of the problem.

    Best regards,
    Raphael
  • 0 in reply to Raphael Mosig
    TI__Mastermind 26485 points

    Raphael,

    Glad I was able to help you find the issue.  Please let us know if you need further assistance.

    Best regards,

    Javier