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INA238-Q1: INA238 no acknowledge (ACK)

mali
Prodigy 20 points
Part Number: INA238-Q1
Other Parts Discussed in Thread: INA238, ISO1540, TCA9517-Q1

Tool/software:

Hi,

In addition to 4 temperature sensor devices communicating over the I2C bus, the PCB also includes an INA238 device.

During I2C communication with the INA238, no acknowledge (ACK) signal is received (the device does not pull the data line low). In contrast, the other temperature sensors on the same I2C bus respond correctly with acknowledge signals, and temperature data can be successfully read from them.

The communication frequency is FSCL ~ 100 kHz, and there is no address conflict among the devices. The circuit schematic is also attached.

Initially, the pull-up resistors on the I2C lines were 1.5kΩ, and the issue was already present. Later, the resistor values were changed to 4.7kΩ, but despite this modification, the INA238 still does not provide an ACK.

The root cause of the issue has not yet been identified.

  • +1
    TI__Mastermind 26345 points

    Hello Mali,

    Th reason the INA238 is not responding is because the output logic low level for the ISO1540 side 1 is too high for the INA238 (which requires a low level of 0.4 volts or below). The output logic low of ISO1540 side 2 has an output low maximum of 0.4V, so if you switch the INA238 to side 2, then you should be within the logic limits. Since those limits are right on the edge, I would also recommend adding 33pF capacitors to GND on the SDA and SCL lines in between the ISO and the INA. 

    If for some reason you cannot swap the ISO sides, then you could add a level shifter, such as the TCA9517-Q1, in between the ISO and the INA (connecting the INA to side A of the level shifter)

    Regards,

    Mitch

  • 0 in reply to Mitch M
    Prodigy 20 points

    Hello Mitch,

    It turned out just as I thought. Before making any cuts or using jumper wires on the PCB, I wanted to consult with you to be sure. I am glad our ideas are aligned. Thanks a lot for your support. For now, I will close the issue without taking up more of your time. If I encounter any problems after testing, I will inform you again.

    Best regars,