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Tlc2272 opel loop gain frequency dependece

Mircea Pop
Prodigy 30 points

Other Parts Discussed in Thread: TLC2272

Dear all,

I'trying to model the frequency behavior of TLC2272 as a first order LPF. Would it be all right to consider the cut-of frequency 10KHz  and Aol=35e3?

  • 0
    TI__Guru 64625 points

    Hi Mircea,

    I think you'll find the answers to many of your questions in the TI Precision Labs Videos on bandwidth, slew-rate, and stability.  The bandwidth videos provide an in-depth explanation on op amp open-loop gain (Aol) including how to calculate the dominant pole from the DC Aol value and the UGBW.

    For the TLC2272 the DC Aol is between 35V/mV (90.88dB) and 50V/mV (93.98dB).  The GBWP is 2.25MHz for the 50V/mV DC Aol so the dominant pole can be calculated as shown below:

    Dominant Pole = UGBW / Aol = 2.25MHz / 50000 = 45Hz.

    Aol.TSC

  • 0 in reply to Collin Wells
    Prodigy 30 points

    I' ve got it; quite straightforward.

    Therefore, for +5V supply, I get fc=62,3Hz. 

    Bu Tina Ti return the atached result hopefully it' visible). Could you please explain the discrepancy?

    Thank you

  • 0 in reply to Mircea Pop
    TI__Guru 64625 points
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  • 0 in reply to Collin Wells
    Prodigy 30 points

    So, the Tina result for an open loop configuration:

    Therefore, most probably, the Tina design or model is not applicable for this purpose; but I'd be interested to find out the answer. Thank you!

  • 0 in reply to Mircea Pop
    TI__Guru 64625 points

    Hello,

    This is not a valid circuit to test the open-loop gain of an op amp.  Without feedback the output will saturate into one rail or the other which will collapse the open-loop gain.  Please go through the TI Precision Labs videos on op amp bandwidth and stability to understand more about op amp open-loop gain and how to simulate it.