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TLC2272M: Worst Case voltage offset for a voltage follower that uses a TLC2272M op-amp

Nigel Fernandes
Prodigy 20 points
Part Number: TLC2272M
Other Parts Discussed in Thread: TLC2272, TLC2272A, TLC2272AM

I am conducting a error analysis on a circuit containing the TLC2272M as a voltage follower in the configuration.I read the datasheet provided at the link http://www.ti.com/lit/ds/symlink/tlc2272m.pdf , and was wondering, on page 8 which input offset voltage must I use; the one for TLC2272 or TLC2272A.

 

My second question is regarding Figure 6 on Page 14, which is tilted Input Offset Voltage versus Common mode voltage. I wanted to confirm that the Input Offset Voltage does change with the polarity of an input signal to a voltage follower. Also I assume this not a graph highlighting the worst case offset voltage, it would be of great help if you could estimate what the graph would look like in a worst case scenario.

 

Also would increasing the dual rail supply above+/-5V to +/-6.9V, effect the shape of the graph, i.e. would the linear region of the graph extend towards +/-6.9V.

 

When reading the TI ebook “The signal: A compendium of blog posts on op amp design topics”, I came across a sentence that I would to understand more about; on Page 5 it refers to that rail to rail op-amps as follows “It can also cause distortion in alternating current (AC) applications. But again, distortion will only occur if the common-mode input voltage crosses the transition between stages.”. Could you explain if applicable how this related to the Input Offset Voltage versus Common mode voltage graph for the TLC2272M

 

Looking forward to hearing with you.

 

Regards,

 

Nigel Savio Fernandes

  • 0
    TI__Expert 6275 points

    1) M is the operating temperature range.  For TLC2272M use TLC2272 specs on page 8.  If you wee using a TLC2272AM then you would use TLC2272A specs on page 8.  

    2) Correct input offset voltage can change polarity based on input common mode voltage.  Curve is typical.  It could tilt positive or negative.  You need to use CMRRR number. Read through attached blog which details the real Vos to consider:

    Will the Real Vos Please Stand Up - FINAL_TG.pdf

    3) Increasing the dual supply rail to +/-6.9V linear region will extend similar relative to data sheet max specs per item 2).

    4) If you run TLC2272M from +/-5V input common mode range is -5V to +3.5V.  If you use it as a follower and put in voltages on the input above +3.5V you will have a huge jump in offset and the front end of the op amp will no longer operate linearly.  Sentence above is more discussing rail-to-rail input single supply op amps.

    See this video for more details about input crossover region:

  • 0 in reply to Tim Green1
    Prodigy 20 points

    Hi,

    Thanks for your quick response, it has solved most of my questions. However, it has a raised a few more:

    1. What would be the effect of the distortion explained in the answer 4, to TLC2272M being used in a inverting or non-inverting configuration. Would it not be effected, because the common mode voltage of the two configurations is close to 0V. Also in general, would the offset curve demonstrated in the offset voltage versus common mode voltage be applicable to the two above mentioned configurations.

    2. Also the video was quite informative, to my understanging a trimmed version of rail to rail op-amps would reduce the gradient of the linear region in the offset curve. Hence, I was wondering if TI offered a Trimmed version of the TLC2272M.

    Regards,

    Nigel

  • 0 in reply to Nigel Fernandes
    TI__Expert 6275 points
    1) Inverting gain CM will be zero so you will not violate the input CM voltage region. Non-Inverting region you must stay within the CM voltage range specified.
    2) It is not just a trimmed version but a different input architecture. We have no "M" grade parts tat are rail to rail in on +/-5V supllies.
  • 0 in reply to Tim Green1
    TI__Genius 11135 points
    Nigel

    We haven't heard back from you so we assume this resolved your issue. If not, post a reply below, or create a new thread if this one has timed-out.

    Thanks
    Dennis