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SN74ACT244: Device Output R

Yuki Ito
Prodigy 55 points
Part Number: SN74ACT244
Other Parts Discussed in Thread: UCC27517

Tool/software:

I am trying to connect several output pins of SN74ACT244 to obtain a drive capacity of more than 100mA. I will be driving a 50Ω termination. I am thinking of attaching a 50Ω resistor to the output of the device, but would it be better to assume that the resistance of the SN74ACT244 output pin + resistance = 50ohms? What will be the resistance of the output terminal per pin of the SN74ACT244? Also, when connecting and driving all the output pins, how much drive should I take into consideration for the input side pins?

  • 0
    Guru 316440 points

    The typical output resistance of one pin is about 10 Ω.

    AC inputs have a worst-case leakage current of 1 µA.

    What is the voltage required at the receiver? With 50 Ω terminations at both the source and the receiver, you get a voltage divider that requires you to double the source voltage.

  • 0 in reply to Clemens Ladisch
    Prodigy 55 points

    Thank you for your answer.
    I need 5Vpp when terminated at 50Ω. In this case it's 2.5Vpp.
    Do you know of any good drivers?
    The frequency is 1Hz as it is 1PPS used in Time generator.
    However, I would like the slew rate to be as fast as possible.
    Thank you in advance.

  • 0 in reply to Yuki Ito
    Guru 316440 points

    To get 5 V at the receiver, you need a 10 V driver. You could use a gate driver like the UCC27517.

    In general, 50 Ω lines are used in a lab where you have function generators that can drive them. In practice, clock signals are typically transmitted with LVDS.