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TTL to 50 Ohm Driver

Other Parts Discussed in Thread: SN74128, AM26C32

I am trying to get a basic circuit for driving a TTL signal to 50 Ohms.  The supply voltage will be 3V to whatever circuitry I use.  One idea was to use the SN74128 (Vcc too high) or the LVC1G126.  I will end up putting enough in parallel to satisfy the current requirement of approximately 50mA at 2.5V output level.  

What is a recommended part for this? I found 49 parts for logic gates that supported a Vcc down to 3V for TTL level logic in/out so was having a hard time narrowing it down.

Thanks,

Priyank

  • The biggest issue here is the amount of required current. If you are running a 5 V output into 50 ohms, you will have 100 mA of drive current required. The only way I know of to get values like this is the connect multiple buffers in parallel, and even then you have to be careful about exceeding a part's rated maximums. Can you be more specific in your system's requirements? A schematic is generally very helpful. Input/output voltages and currents and number of channels required are also a big help in part selection.
  • We will NOT be running a 5V output into 50 ohms. The main requirements:
    1. The input of this circuit is logic level from the output of the AM26C32 (looks like Voh 3.8V)
    2. The output of this circuit needs to stay below an absolute max voltage of 3.3V, which is why I originally stated 2.5V output (sorry was vague on what output).
    3. The output of this circuit needs to have matched to 50 ohms, so I need to source enough current for this to work. (50mA if the output voltage is 2.5V)

    I have 3 channels, but I can just create 3 identical circuits if necessary.

    Thanks,

    Priyank