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OPA4H014-SEP: datasheet figure 6-15, open-loop gain vs temperature

Maurits Rijnders
Prodigy 10 points
Part Number: OPA4H014-SEP
Other Parts Discussed in Thread: OPA4140, , OPA4H199-SEP

Tool/software:

The graph of this opamp has unusual units for the y-scale:

I would assume these values are relative to typical OL gain,

but units in [dB] is what I would expect in this case, not [mV/V], which seems extremely small for open-loop gain.

[V/mV] would make more sense maybe?

Comparing this to the non-space variant of this opamp, the OPA4140

This seems an identical graph, except the units are even stranger: [uV/V] !

The list of specifications of the OPA4H014-SEP suggest a range of 108 - 125 dB [200.000 - 1000.000 V/V] for OL gain,

so I would expect to see something similar in the graph above.

An example would be this graph from the OPA4H199-SEP,

Which makes a lot more sense.

Please let me know if I'm interpreting something wrong here.

Best regards, Maurits

  • +1
    TI__Guru* 77501 points

    Hi Maurits,

    Maurits Rijnders said:
    but units in [dB] is what I would expect in this case, not [mV/V], which seems extremely small for open-loop gain.

    Yes, this is Aol vs. temperature plot, where the mV/V can be converted in dB loses or gain vs. temperature. The Aol plot seems to use at approx. ~0 mV/V as the mV/V loss reference at -55C. 

    For instance, with 10kΩ load, assume the Aol is the reference with approx. 0mV/V. At 25C, loss is -0.2mV/V or loss is 20*log(0.2mV) = -14dB. 

    If I subtract Aol = 1260dB (typical at 25C), the Aol is approx. 112dB. The part guarantees the minimum Aol will not be less than 108dB at 125C under the specified load and temperature condition, which is 125C. 

    Maurits Rijnders said:
    Please let me know if I'm interpreting something wrong here.

    You are not wrong here. Yes, it adds confusion somewhat. These datasheet is put together from different engineers or even different teams, and not all these engineers have the same intuitive senses when someone plotted this. It is also possible the plot was left over from the initial datasheet phase in the non-EP product, and remained as is when the -EP datasheet was put together and published in recent years. 

    I agree with you that this plot should have presented it in a clearer perspective and there is no need to make the Aol parameters as confused as it was presented. 

    If you have additional questions, please let me know. 

    Best, 

    Raymond

  • 0 in reply to Raymond Zhang1
    Prodigy 10 points

    Hi Raymond,

    I'm still a bit confused, if 126 dB is the typical value @ 25C why would you still need to subtract 14 dB?

    Further, if I use your method: when there is a -0.4 mV/V loss and I use the function 20*log(0.4), the result is -8 dB which is less than 20*log(0.2) which results in -14 dB. At a higher temperature I would expect a bigger loss.

    ~ Maurits

  • 0 in reply to Maurits Rijnders
    TI__Guru* 77501 points

    Hi Maurits, 

    I meant to say that at -55C, the Aol should be 126dB + 14dB, which is approx. 140dB, if I use 25C data as typical Aol reference for 10kΩ load. 

    At 125C, the Aol is 126dB - 8dB is approx. 118dB as typical, and the datasheet guaranteed that the worst case in Aol will not be less than 108dB for 10kΩ load. 

    Please let me know if you have other questions. 

    Best,

    Raymond