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PCA9306 I2C Level Issue

Kinjan Patel
Prodigy 210 points
Other Parts Discussed in Thread: PCA9306

Hi

I am Using PCA9306 to translate I2C Bus voltage from 3.3V to +5.0V. But when i Power up my board the voltage on both side rises to almost 4V. As a part of debugging i removed this IC and found voltage recovered on both the sides.

Referring to http://e2e.ti.com/support/interface/etc_interface/f/390/t/116981.aspx, i tried replacing the pull up of enable as 1ME and replacing the Pull up of I2C Bus Vref2 section as 5.6K, but issue not solved.

Please let me know what could be the cause. Schematics is attached here.

6170.I2C Level Shifter-PCA9306.pdf

  • 0
    TI__Intellectual 1930 points

    Kinjan,

    accoriding to your diagram, Vref2 is directly connected to Vcc and there is a resistor between Vref2 and EN.

    If you look at the application diagram on the DS you will see that there should be a resistor in between Vcc and Vref2 and Vref2 should shorted to EN.

    I believe this change will fix your problem.

    Thanks,

    Akhil.

  • 0 in reply to Akhil Nair
    Prodigy 210 points

    Hi Akhil,

    Thank u very much for your reply.

    I have made the changes and my issue is resolved.

    But please explain me why is that voltage changed to 4V instead of 3.3V and 5V on either side only because Vref2 is not pulled with resistor.

    Can u explain the technical reason behind this.

    Kinjan

  • 0 in reply to Kinjan Patel
    TI__Intellectual 1930 points

    this is a detail of the design implementation.. in your old set up you were essentially the source and drain of a MOS with vgs>vt... resulting essentially in a short between vref1 and vref 2. by putting a resistor in series it is not a short anymore.