Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice User Guide Convergence and "time step too small errors" October 2019 845 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. GMIN stepping attempts to find a solution by starting the repeating cycle with a large value of GMIN, initially 1.0e10 times the nominal value. If a solution is found at this setting it then reduces GMIN by a factor of 10, and tries again. This continues until either GMIN is back to the nominal value, or until PSpice fails to converge at one of the GMIN values on the way. In the latter case, GMIN is restored to the nominal value and the power supplies are stepped. ■ Power supply stepping As previously discussed, PSpice uses a proprietary algorithm which finds a continuous path from zero power supplies levels to 100%. It starts at almost zero (.001%) power supplies levels and works its way back up to the 100% levels. The minimum step size is 1e-6 (.0001%). The first repeating series of the first step starts at zero for all voltages. So modeling expressions, especially those having denominators that include voltages should be checked carefully. ■ Set PREORDER in Simulation Profiles options This is important while editing schematic for marginally convergent circuits. Setting PREORDER reduces dependency on the netlisting order thereby ensuring that the non convergence error does not occur because of the change in the netlisting order. DC Sweep Convergence The DC sweep uses a hybrid approach. It uses the bias point algorithm (varying the power supplies) to get started. For subsequent steps it uses the previous solution as the initial approximation. The sweep step is not variable, however. If a solution cannot be found at a step then the bias point algorithm is used for that step. The whole process relies heavily on continuity. It also requires that the circuit be linear when the supplies are turned off. Circuit topology and connectivity This is same as in DC analysis. See Checking circuit topology and connectivity on page 841.