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TLE2061/TLE2062 Open-loop Output Impedance mismatch between TINA model and Datasheet

Shihab
Expert 1205 points
Other Parts Discussed in Thread: TLE2061, TLE2062

Hi,

As per datasheet the open-loop output impedance of TLE2061 and TLE2062 are 280 ohm and 560ohm respectively. But in TINA simulation I am getting open-loop output impedance as 140ohm. Can you please clarify why there is a conflict between datasheet as simulation?. I attach the simulation file (TLE2061_Zo.TSC)  for your reference.TLE2061_Zo.TSC

  • 0
    TI__Guru* 93105 points

    Hi Shihab,

    The TLE2061 and TLE2062 simulation models are 1990 Boyle models and accurate open-loop output impedance Zo wasn't a consideration, or a capability, of the model. Therefore, the Zo you obtained from the above TINA simulation are most likely incorrect. The other problem is the TLE2061/TLE2062 datasheet lists Zo in the Electrical Characteristics table as 280 Ohms for the TLE2061 and 560 Ohms for the TLE2062 (Io = 0 A); however, they use the same push-pull, emitter follower output stage design and should have nearly identical Zo.

    Push-pull emitter follower output stages usually exhibit a resistive Zo at very low frequencies and over much of their usable bandwidth. They tend to turn upward at some high frequency exhibiting a resistive plus inductive characteristic. When we take the TLE2061 closed-loop (Zcl) output impedance frequency graph, Fig. 22, in the datasheet, the linear slopes confirm a resisitve characteristic for the open-loop Zo over most the frequency range. An estimate of the Zo based on the linear region gives a value of about 350 Ohms. Note that Fig. 23 for the TLE2062/64 looks like its vertical scale is too low by a factor of 10x so it appears to be incorrectly labeled. 

    We are going to obtain some TLE2061 and TLE2062 devices and take them to the lab and measure their open-loop Zo. That will take about a week. I'll report back here with the results.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Guru* 93105 points

    Hi Shihab,

    Please see the TLE2061 open-loop Zo graph we received from measurement. With a back-drive current of Iq/2 (145uA) the Zo flattens off to roughly 175Ω which is less than the datasheet value of 340Ω from the figure, 280Ω from the spec table. The TLE2062 uses the same output stage so the Zo should be the same.

    As one of my colleagues who was involved in the Zo measurement pointed out you should be able to add a 35 ohm resistor in series with the TLE2061 simulation model output pin and have a reasonably good approximation of the real product's Zo. Add the resistor right after the output pin and inside the feedback loop.

    Regards, Thomas

    PA - Linear Applications Engineering