LTspice Models of ADA4097..ADA4099: Wrong Shutdown behaviour

Question

Hello,

it seems that activating shutdown on these OpAmp models does not switch the outputs to tristate mode as described in the datasheet, but connects them to GND instead.

This can be demonstrated by driving the output with an external voltage source (via a resistor).

When shutdown is activated, the output is held at 0 V, even though no other pin of the opamp is connected to GND.

LTSpice test schematic attached.

ADA4099-1-Shutdown-Test.asc

tgreen_AZ · Accepted Answer

I have confirmed that the macromodel does not correctly reflect shutdown behavior. Depending upon how you are planning on using the device be aware that almost any op amp in shutdown mode will have a high output impedance at DC but it will become lower as frequency increases due to parasitic capacitance in a real device. Unfortunately, the ADA4097 and ADA4099 do not have a Disabled Output Impedance Curve vs Frequency so the model cannot be updated until that data is taken in the lab. This will be submitted into a backlog queue for model fixes. It could take several months for the fix to be implemented based on other models in the queue. To see the typical characteristics of a disabled output impedance over frequency consider looking at the ADA4523-1 datasheet, page 14, Figure 32: ZOUT vs. Frequency in Shutdown.)

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LTspice Models of ADA4097..ADA4099: Wrong Shutdown behaviour