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PCA9306 problem

Nicola 76855
Prodigy 50 points
Other Parts Discussed in Thread: PCA9306

 

 

Hi all,

I am working on the PCA9306, I2C bus voltage shifter and I am facing with a strange behavior. 

The master on the I2C bus works at 3.3V and the slave works at 5V. 

In the picture attached you can find part of the electrical scheme. Y2 connector is provide the connection with the master board where the 4K7 pull-up resistors are placed.

When I power-up my system the voltage on VREF1 rises to 4.2V.

I tried to remove the PC9306 in order to check that 3.3V LDO is working well, and that is true.

I tried to connect only the VREF2, EN, SDA2, SDL2 and GND and then check the voltage on VREF1: the value found is 4.2V.

I tried to change the value of the pull-up on EN pin (connected to VREF2) and I notice no changes.

I think my case is similar to this one: http://e2e.ti.com/support/interface/etc_interface/f/390/t/33915.aspx

 

Could you please give me and advice in order to solve my problem?

 

Could be a power-up sequence? (Before VREF2 and then VREF1)  

 


Thank you very much in advance.

 

  • 0
    TI__Intellectual 1930 points

    Nicola,

       Your circuit seems correct, and it shouldn't be seeing the problem you describe. have you seen thi sproblem with a single PCA9306 have you seen this problem with all multiple PCA9306 devices?

    REgards,

    Akhil.

  • 0 in reply to Akhil Nair
    Prodigy 50 points

    Akhil,

     

    thank you for your reply. I found the same behavior trying two different devices placed on two pcbs.

     

    This morning I will try some test and I will let you know the results.

     

    Did someone found same problems using this kind of device?

     

    Thank you and regards,

     

    Nicola

  • 0 in reply to Nicola 76855
    Prodigy 50 points

    Akhil, 

     

     after a couple of test the result is the following: in order to have a good bus communication the pull-up resistor (on both side, 3V3 and 5V) are 5K6 resistors. The pull up on VREF2 (connected together with EN) is 1Mohm.

    What do you think about?

     

    Thank you very much and regards.

     

    Nicola

  • 0 in reply to Nicola 76855
    TI__Intellectual 1930 points

    Nicola,

    Glad you were able to get your problem resolved... unfortunately I wasn't of much help. We will repeat the test in the lab to see if we can reproduce the problem you were seeing and understand the root cause. You whouldn't have been seeing the problem.

    Regards

    Akhil.