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SN74AHCT14: damping resistor

Part Number: SN74AHCT14

Hi

Our customer are considering the damping resistor. If the Pin#4(output of channel 2) is connected to Pin#1(input of channel 1), should we add the dumping resistor between Pin#4 and Pin#1?

I think the pattern trace is very short and does not need. (signal freq:120kHz. the trace is connected as possible as short.)

Regards,

Koji Hamamoto

  • Hi Hamamoto-san,

    What you have described is the correct way to add a damping resistor.

    Typically, a damping resistor is added to reduce reflections due to impedance mismatches, but in the case you have described, the ringing is more likely caused by the light load and some parasitics.  The two cases are shown below:

    It seems unusual for there to be excessive ringing when connecting two channels of the same device in series. Can you tell me more about the application? 

  • Hi Emrys-san,

    Thank you for your prompt reply.

    I don't have more information about the customer application now. Only information what I have is ;
    Signal Freq : 120kHz
    Supply voltage : 5V
    Trace pattern width : 0.18mm
    Trace is as possible as short.

    The customer would like to reduce the components as possible if it is not necessary. Because the trace is very short when connecting two channel of the same device in series.

    Regards,
    Koji Hamamoto.
  • I doubt that they will need a damping resistor, especially with such a slow signal.