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PCA9555: Polarity Inversion questions

xingchang pang
Prodigy 20 points
Part Number: PCA9555

We found that the I/O ports active HIGH  in default when PCA9555RGER is powered on at room temperature,

However，It will active LOW  when it is powered on at high temperature +60-85 degrees for a period of time. What is the reason ，Why the Polarity is Inversion at different temperature ?

During the test, the MCU did not send any configuration command to PCA555 through I2C. I removed the I2C line and only validate the default status for PCA555 .

  • 0
    TI__Mastermind 49110 points

    Hi Xingchang,

    Do you have scopeshots of the Vcc ramp rate at room temperature and the high temperature?

    The PCA devices can see issues with powering up in non-default state if ramp rate is too slow or if you power up from mid rail instead of GND.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi Bobby

    Thanks for your kindly reply!

    As you said，the waveform of Vcc at high temperature is different with room temperature . So， the anomaly has been exposed， Please find the scope shots below and help to comment how to solve these issues .

    Picture 1 : It Shows the scope shot at room temperature，yellow line is indicated VCC and green line is for I/O port.

     

    Picture2: Shows it at high temperature，obviously， vcc is abnormally.

    Xingchang

    Best regards!

  • 0 in reply to xingchang pang
    TI__Mastermind 49110 points

    Hey Xingchang,

    Is your picture 1 the same as picture 2? It looks like the same image since the green waveform goes low after power up in picture 1.

    Is it possible for you to switch to the TCA version of this device? 

    The rising edge rate looks like its slow and messing with the PoR circuit for the device. TCA version is more lenient with the ramp rate than PCA. 

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 20 points

    Hi Bobby

    Yes ，both are the same，is the upload error.

    Actually ，I am planing to use PCA as the alternative for TCA, Could you please advise other alternative .

    xingchang

    BR

  • 0 in reply to xingchang pang
    TI__Mastermind 49110 points

    Hi Xingchang,

    Do you need to be pin to pin with TCA9555RGE? 

    Do you need 16 bits? 

    (This may be tricky since it looks like all the TCA RGE packages are out of stock....)

    -Bobby