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Parisite capacitor input for TLC339 and TLC374

Yves Camille
Prodigy 40 points

Other Parts Discussed in Thread: TLC374, TLC339, TLV3401, TLV3701

Dear support,

I am looking for the value of the input parasitic capacitance for both the TLC339 and TLC374 - this is not shown in the documentation

Thank you - Yves Camille - Arrow Electronic

 

 

  • 0
    TI__Guru* 93105 points

    Hello Yves,

    The input capacitance of comparators such as the TLC339 and TLC374 is seldom specified, or even characterized. The capacitances associated with the CMOS input differential pair(s) and  ESD protection cell are small; usually on the order a few picofarads which can be difficult to reliably measure. Then, there are the issues of how this capacitance changes realtive to the input level and the input swing range, and where to specify it because everyone's operating conditions are different. Likely, the capacitance is in the neighborhood of 5pF, or less, as a rough estimate.

    Is the input capacitance a concern in the customer application? If so, tell us more about the application and we can better assess the concern.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Genius 5430 points

    Tom;

    Yes, it is important and the input capacitance should be in the data sheet as well as in the device macromodel.

  • 0 in reply to Neil Albaugh
    TI__Guru* 93105 points

    Hi Neil,

    Agreed - you and I have been involved with enough simulation model developments to know the importance of accurate models. Today, we strive to make our simulation models behave as correctly as possible. However, the TLC339 and TLC374 simulation models were developed over 20 years ago and the models are consistent with models of the time - they are simple models.

    If you open the Pspice listing the input devices use the Qin transistor model. Very few parameters are specified, and none are specified for any of the transistor capacitances; and I do not see any added capacitances as well. Thus, the junction capacitances default to zero - which in reality isn't the real case. "Real" CMOS device models based on characterization are about the only way to capture the input device's true electrical characteristics. But then again you know this!

    We are working with TI's eLab to build models for linear products that have never had one. You may have seen the TLV3401 and TLV3701 comparator simulation models were introduced last year. These are very popular comparators that never had simulation models. And presently, we are working on simulation models for 3 older, TI comparators and several somewhat older amplifier products. So, resources permitting, we may be able to do something about updating older, pre-existing simulation models too.

    Happy holidays and thank you for all your contribution to the E2E forums this past year!

    Thomas

    PA - Linear Applications Engineering