PSPICE-FOR-TI: Convergence occurs when simulating dual power supplies with the INA821.

Hi Leo,

simulators are extremely sophisticated and use many hidden tricks to perform the simulation with highest precision and lowest run time. To achieve this they optimize the simulation parameters during the run. If your circuit is simple and contains only a few chips, this will work without any problems. But if you have two or more chips in your simulation which need very different simulation parameters the simualtion can either fail or need extremely long to end. This is common to all simulators I know and need not have to do with mistakes of the individual models of chips.

It's a standard mistake to put too many chips into the same simulation and expect a short run time. The remedy is very simple: Divide your project into small portions and simulate them individually. So, don't supply chips with LDOs or even "switchers" (very bad) being simulated at the same time. Also, simplify input and output signals so that you need not to feed the output signal of one OPAmp to the input of another OPAmp. Many real signals can be modelled by the simplified signal shapes the simulator already offers to you. In most cases there's no need to simulate every true and real signal appearing in the circuit.

Divide and conquer!

Kai 

There's another widespread misunderstanding: Due to imperfections of models, simulators and the simulation itself (not containing any relevant stray capacitances, etc.) a simulation is never telling the whole truth. It cannot be overemphasized that the results of a simulation must always be confirmed by true measurements on the real circuit. Be prepared to see many surprises when doing the measurements on the real circuit, almost always forcing you to modify your design.

A simulation is only a more or less helpful tool but it is not the holy grail.

Kai