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PCA9535 POR I2C Latching issue

Will Jarrett
Expert 3395 points
Other Parts Discussed in Thread: PCA9535, TCA9535

I have a customer who is experiencing some issues with the PCA9535 latching the I2C_Data bit low during a power droop of the VCC. In the application, the Vcc decays very slowly and takes about 2 seconds to decay from 3.3V to 200mv. It appears that if Vcc is re-applied before it decays below the 200mv POR threshold, that the IC can come back up in a latched state. The Data will remain latched until Vcc is removed.

Is this expected? Are there any work-arounds other than removing Vcc completely then re-applying power?

  • 0
    TI__Genius 9085 points

    Hi Jarrett,

    The PCA9535 is known to have some POR issues which were cleared up in the TCA9535. I would encourage the customer to switch to this part, which is identical in functionality and pin out.

    Please let me know if the change does not clear up the problems you are seeing. 

  • 0 in reply to Hattie
    TI__Expert 3395 points

    Hi Hattie,

    Would a discharge resistor resolve the problem?  Can you give any specifics about the POR issues on the PCA9535 and how to resolve them?

    Thanks!

    -Jarrett

  • 0 in reply to Will Jarrett
    TI__Genius 9085 points

    Jarrett,

    For the PCA9535, the discharge resistor should solve your problem if the TOFF(time below 200mV) is > 100ms and the TRISE < 10ms.

    The TCA9535 can support any TOFF and TRISE time.

    Although the voltage does not drop below the 200mV, I suspect the more robust design of the TCA part would not exhibit the same latching behavior, and I will take some time today to try and confirm that. For now, your discharge resistor is probably the best solution.

    Regards,

    Hattie