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MAX3222: output has a step

ACGUY
Guru 11170 points
Part Number: MAX3222

Hello E2E,

Our customer is evaluating MAX3222IPWR got after PCN for this device.
The device befor PCN has not a step on output waveform, the device after PCN has a step on output.

Does TI know about this event?
Does this event cause an electrical defect?

Best regards,
ACGUY

  • +1
    TI__Guru 57730 points

    Hi ACGUY,

    I have a guess as to what may cause a waveform like this... 1) The PFET driving HIGH is partially turned on while the NFET driving low is transitioning on resulting in some contention between the two for a small amount of time resulting in this step you're seeing. 2) There is some kind of pass FET architecture on the output (like a level shifter or MUX) resulting in the two sides of the level shifter/MUX waiting for the capacitive loading to equalize. I assume #2 isn't the case since it's rare for RS232 output signals to be MUX'd/shifted..... 

    I've assigned this thread to one of our RS232 experts to comment on but in the mean time, could you please provide answers to the following:

    A) Is this waveform you're seeing occurring in multiple devices (10 out of 10 or only 1 out of 10 for example?)

    B) Do you have a schematic we can review? 

    -Bobby

  • 0 in reply to BOBBY
    Guru 11170 points

    Hi Boby,

    Thank you for reply.
    A) 5 samples. Occurred in all. That step is extend by temperature.
    B) I pasted.

    Regards,
    ACGUY

  • 0 in reply to ACGUY
    TI__Mastermind 25705 points

    ACGUY,

    What's the load of TOUT? Other than the diodes, are there any other load? How long is the cable? 

    Regards, 

  • 0 in reply to Hao L
    Guru 11170 points

    Hi,

    This circuit has not load, it is open.

    Regards,

    ACGUY

  • +1 in reply to ACGUY
    TI__Mastermind 25705 points

    ACGUY,

    Thanks for your information. The reason of the step is like #1 point Bobby mentioned. Given the voltage level and slew rate are complied with the RS-232 standard, this behavior should not impact system performance and it raises no reliability concerns either. 

    Regards,