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INA238: may receive NACK sometimes

ZYT
Prodigy 90 points
Part Number: INA238


We use cypress mcu to read voltage and current from INA238 in our project, it works well most of the time, but mcu will receive NACK signal when read continually.

Below is the normal and failed scope. What may the problem is? Thanks.

normal scope:

NACK scope:

  • 0
    TI__Mastermind 27860 points

    Hello,

    Thank you for using the TI forum. It is possible that you have a timing issue. Could you send another scope shot of the failed communication that includes the start of the I2C communication, including the device addressing?

    For reference, I've pasted the the I2C timing requirements below. Also, per the datasheet, "When connecting the SDA pin to either A0 or A1 to set the device address, additional hold time of 100 ns is needed on the MSB of the I2C address to insure correct device addressing."

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Prodigy 90 points

    Hello Mitch, thanks for your reply.

    Below is the integral scope. It looks there is a continuous low level when read register, and restart with that.

    Will that make error?

  • 0 in reply to ZYT
    TI__Mastermind 27860 points

    Hello,

    Having the continuous low clock will not cause a problem. From this scope shot, it looks like the communication completed successfully though. I recommend zooming it to look at the specific timing on both halves of the communication to make sure that they align with the datasheet. Also, look at voltage thresholds as well. If you are still having issues, try slowing down your communication and see if the problem goes away. (This can help rule out some timing issues).

    Regards,

    Mitch