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Tool/software: TINA-TI or Spice Models
I am investigating supply decoupling of signal related currents in op-amp circuits driving a low impedance load. I have noticed that the AC transfer characteristic gives implausible results for some op-amps, and these implausible results disagree with the oscilloscope view of the power supply current waveforms. For example, comparing TLV2461 and LMV321 in the same circuit driving series 50R + 220U to 0V, the supply current waveforms at 10kHz are identical but the AC transfer characteristic says the signal current in the power supply is -40dB (i.e. 10mA) for TLV2461 versus -34dB (i.e. 20mA) for LMV321. The peak current measured on the 'scope is 20mA in both cases. This is shown in the screenshot below.
I have obtained more bizarre results with other TI op-amps, some of which give completely implausible current waveforms on the 'scope, e.g AC signals of nano amps magnitude, or sinusoidal current waveforms that are different in each power supply feed (thereby violating Kirchoff). It seems the op-amp models or TINA-TI (or both) do not always simulate power supply currents correctly. Any solutions?
Hi Herman,
Thanks for your reply. So I think you are saying it is an issue with some of the op-amp models, rather than TINA-TI software? Does that mean I am out of luck with respect to any sort of solution to this issue? It is not just op-amp models from TI that have this issue. If I use a personal favourite from LT (over a decade old), that also gets the supply currents completely wrong in TINA-TI. Is it too much to hope that TI will update its older models to better represent the performance of current product offerings?