LTC2050 Demo Circuit

Question

I downloaded this demo circuit from https://www.analog.com/en/design-center/evaluation-hardware-and-software/lt-spice-demo-circuits.html 
 When I attempt to run the simulation it never converges. Any suggestions? Thanks. 
 The demo is tilted "LT6200 & LTC2050 Demo Circuit - Low Noise, Low Power Photodiode Transimpedance Amplifier with DC Precision"

helmuts · Accepted Answer

Hello, 
 I tested this schematic and indeed the simulation doesn't start due to a convergence problem. The reason may be that one of the opamp models have changed since the schematic had been created. 
 When LTspice starts a simulation, it firstly try to find the DC-operating point. The table below shows the order and the methods which are used. 
 From the help pages:

Method 
 Directive to disable

Direct Newton Iteration 
 .options NoOpIter

Adaptive Gmin Stepping 
 .options GminSteps=0

Adaptive Source Stepping 
 .options SrcSteps=0

Pseudo Transient 
 .options pTranTau=0

The circuit simulation with the circuit LTC2050_LT6200_DN308F2.asc fails with all four methods. 
 I often try then with the pseudo transient option "ptrantau". 
 .options ptrantau=100n 
 LTspice has now found the DC operating point after some time, because it tried the three other methods before. One can skip the thirst three methods to quickly get the simulation done. See the combined SPICE-directive below. 
 .options noopiter gminsteps=0 srcsteps=0 ptrantau=100n 
 Helmut 
 I have attached the circuit with the added SPICE-directive. 
 
 LTC2050_LT6200_DN308F2_ptrantau.zip)