Tie inputs and output of OTA together and apply voltage to this node?

[treez]

An "Operational Transconductance amplifier" (OTA) outputs a current proportional to the voltage difference between its inputs.

Therefore, if i apply the same voltage to both inputs...then the output current is zero.....therefore, the output impedance must be at maximum, and therefore, i can simply apply the same voltage thats at the inputs to the output aswell?....and not cause any damage to the OTA?

 

[BradtheRad]

The op amp turns on either the upper or lower transistor, to the extent which maintains 0V (for your scenario). It has internal circuitry which tries to do so regardless of load.

And the load is connected to unknown voltage and unknown resistance. This means output impedance is not necessarily predictable. Supposedly the internal circuitry adapts to any condition, to create an output voltage which drives the inputs so they're equal voltage to each other.

Perhaps with no load the output impedance is maximum. However that's like saying the output goes to high impedance, and I'm not sure if an op amp really creates 0V by shutting off its output stage. And I'm not sure how we would measure what it's doing, since whatever we attach makes it alter what it does.

 

[treez]

Thanks, as you know, "Voltage mode" opamps with negative feedback, almost always drive their outputs to an extent which results in their inputs becoming at the same voltage....this is not so for OTA's.
this is the root of it, and the root of the difficulty in "inflicting" a certain voltage to the output of an OTA.

You would think with an OTA, you could just put say a 1V difference between its inputs....and then, say if the transconductance was "1mA per Volt", then you could put a 1k resistor on the output of the OTA, and the output of the OTA would then stand at 1V...but this is not the case......the OTA is a complicated animal.

 

[treez]

The OTA inside the LT8312 IC has a maximum possible output current of 63uA......How could we have possibly calculated this from the LT8312 datasheet?

LT8312 datasheet

https://www.analog.com/media/en/technical-documentation/data-sheets/8312fa.pdf