I was working on some example sims in just a diff voltage amplifier and kind of needed how much Icm current is available - the TINA model seems to support 1mA demand before it falls apart. Surprised this spec is not there (or at least I cannot find it) Not sure I want to use the 1mA number as model only. Any better min number available for design purposes.
No answer yet, here is what I have for this sans data. Let me know if I need to change this,
This device might also be used to gain up a small differential signal on top of a larger CM source that varies with time. In this case, the maximum input Icm current for the CM voltage range must be lest than the maximum available internal Icm cancelling current. The specification does not appear in the data sheet but up to 1mA is supported in the simulation model. Backing that maximum off to a safe +/-800uA maximum, use that to design a gain of 10 stage with +/-2V input common mode range. That will then require a 2V/.8mA = 2.5kΩ input resistor with a 25kΩ feedback Rf. These higher R’s will require some compensation. Here, I have added a feedback Cf to give a 1MHz pole then added a differential input C that will shape the noise gain to 10V/V at higher frequency (ref. xx). The input Icm servo loop is cancelling the input 800uA of CM current to hold the input pins at 1V.
Figure xx. Differential gain of 10V/V with +/-2V CM reject.
Hey Alec, I am seeing a pretty large differential offset in this simulation, even reducing the Icm demand and resetting the input Vicm to 2.5V. Any idea what is going on here?
