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SN74AVCH4T245: Strong characteristics comparison for noise of LSF0204RUTR and SN74AVCH4T245PWR

Anthony Yoo68
Expert 1320 points
Part Number: SN74AVCH4T245

Hello


My customers are using LSF0204RUTR in their circuits, and the UART communication error is intermittent due to power source noise or GND instability.


My customer would like to review SN74AVCH4T245PWR as an alternative, and is the SN74AVCH4T245PWR more favorable for these power-noise or GND instability?


Or if the characteristics of both products are not different for this noise, could you give me a tip that can be supplemented with the application circuit configuration?

Thank you

Best regards

From Yoo

  • 0
    TI__Guru* 96591 points
    Hi Anthony,
    Can you provide scope shots of the Vcc, GND, and I/O pins showing this issue?
  • 0 in reply to Emrys Maier
    Expert 1320 points

    Hello

    Thank you for your reply~

    I can ask for scope shots on the customer side, but I do not have it at the moment. 

    Is there a difference in specification between the two products, which one is better for noise?

    Thank you

    Best Regards

  • 0 in reply to Anthony Yoo68
    TI__Guru* 96591 points
    These two devices operate in a fundamentally different manner. Without seeing how the noise is affecting the signal, I don't think I can say one way or the other.
  • 0 in reply to Emrys Maier
    Expert 1320 points

    Hi, Emrys

    Below are photos of Noise provided by customers. After checking the waveform below,

    Can you advise me which of the above two products is more suitable?

    Or can you advise me about the circuit configuration that can reduce the noise?

    Thank you

    Best Regards

    From Anthony

  • 0 in reply to Anthony Yoo68
    TI__Guru* 96591 points
    Hi Anthony,
    What you're seeing on the UART_RX line is not noise -- this is bus contention. Something else is connected to that line that is pulling the line down. I can tell this because the other lines do not have the same effect, but they are connected the same. Also, the "noise" appears to be a very specific signal and is over 1V in value... that's far from typical cross-talk. You can also see that the line is held high at one point, which is not possible with capacitive cross-coupling noise.

    You can estimate the strength of the driver by observing the result of the voltage divider produced.

    The pull-up shown doesn't have a value associated with it, so I can't do the calculation for you, but if you do know the resistor value, you can easily determine the driver strength by using this equation:

    Vout = VDD_MCU_3V3 * R2/(R1+R2)

    Vout = the voltage measured at the output, it looks like about 2.5V from the scope shots provided.
    R1 = pull-up value
    R2 = solve for this value to get the drive strength of the offending device.