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SN74LV175A: Maximum Load capacitance

Part Number: SN74LV175A

Hi;

What is SN74LV175APW outputs' maximum load capacitance?

Regards;

Karo Aivazian

  • Hello Karo,
    We recommend keeping load capacitance at or below 70pF, however there is no hard limit.

    Can you tell me more about the application? What is your primary concern with the output load increase?
  • Hello Emrys, Thank you for the response and sorry for the late reply.
    Outputs of the SN74LV175A are connected to up to 16 MMIC RF switches control lines and usually we put a small by pass capacitors next to RF switches control pins. Control lines speed is very low. I 'm planning to go with 15pF x16, which means overall we'll have ~240pF capacitance on the output of the SN74LV175A.
    You mentioned that they are no hard limits, can I assume 240pF is not gong to cause any issues?

    Best Regards;
    Karo
  • Hi Karo,
    It's really going to depend on the tolerance of the inputs to the MMIC switches for slow inputs. CMOS inputs typically require ~10ns per volt edge rates, and at 240pF you're probably outside that range.

    A quick way to estimate is through the RC at the output: C = 240pF, R ~= 58 ohms. I'd expect the 10-90% rise time to be ~4*RC = 55.7 ns. Assuming a 5V operating voltage, that's kind of borderline, but probably won't cause any issues. If it were my system, I'd add some buffers and split the signal up to give ~70pF per buffer.
  • Hi Emrys, thank you again, I appreciate all your help. I'll go with your suggested solution.

    Best Regards;
    Karo.