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TCA9555: Output signal flip in the interference test

Lacey Lin
Intellectual 2900 points
Part Number: TCA9555
Other Parts Discussed in Thread: PCA9555

Hi Team,

My customer are doing the interference test for the TCA9555. The procedure is as below:

1. power on the part and transmit the data between the MCU and TCA9555.

2. Use the 50MHz, sinusoidal wave to interfere the communication, and the link between the MCU and TCA9555 will be broken. the MUC can not identify the part.

And then, the output of the TCA9555 will be flip randomly. such as for logic 1 to logic 0.

So can you help to reply the question:

1. Does the behaver make sense?

2. How can our part to keep the same logic when the link is broken?

Lacey

Thanks a lot!

  • 0
    TI__Guru 73331 points
    Hey Lacey,

    During this test is the device powering down and then back up? It is possible for the device to start up improperly where the registers are not initialized properly and can affect the output of the device.

    How large is the sine wave of the 50MHz signal? is it from 0 to Vcc or something like 100mVs?

    After the test is done, is it possible to send 9 clock pulses and a stop condition and then trying to re-initiate communication?

    --------------------------------------------------
    1. Does the behaver make sense?
    -This behavior is not normal. But this type of testing is not something our device normally sees.

    2. How can our part to keep the same logic when the link is broken?
    Sending 9~18 pulses on the SCL line may help re-establish the link again, from there you would have to reconfigure the registers to the desired output.

    -Bobby
  • 0 in reply to BOBBY
    TI__Intellectual 2900 points
    Hi Bobby,
    The test is done when the part is powered on and are commenting with the MCU.
    Because the PCA9555 are used in the Base station, so they need to do the test.
    They said the sine wave is 5V.

    So the customer wants to if there is some function in our part that can latch the output status while the link is broken by the interference.

    Lacey
    Thanks a lot!
  • 0 in reply to Lacey Lin
    TI__Guru 73331 points
    Hey Lacey,

    Our device does not have that kind of function. It was meant to keep it's outputs during normal operation however it seems like the testing the customer is doing is causing the device to glitch.

    The 5V sine wave is likely confusing the state machine and getting it stuck. I'm wondering if the high frequency is coupling through parasitics into our internal registers.

    -Bobby
  • 0 in reply to BOBBY
    TI__Guru 73331 points
    Lacey,

    Do you have scopeshots of the SCL and SDA lines during communication when you turn on the 50MHZ sine wave?

    -Bobby