Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice User Guide Convergence and "time step too small errors" October 2019 847 Product Version 17.4-2019 © 1999-2019 All Rights Reserved. Transient Convergence The transient analysis starts using a known solution - the bias point. It then uses the most recent solution as the first guess for each new time point. If necessary, the time step is cut back to keep the new time point close enough that the first guess allows the Newton-Raphson repeating series to converge. The time step is also adjusted to keep the integration of charges and fluxes accurate enough. In theory the same considerations which were noted for the bias point calculation apply to the transient analysis. However, in practice they show up during the bias point calculation first and, hence, are corrected before a transient analysis is run. The transient analysis can fail to complete if the time step gets too small. This can have two different effects: 1. The Newton-Raphson iterations would not converge even for the smallest time step size, or 2. Something in the circuit is moving faster than can be accommodated by the minimum step size. The message PSpice puts into the output file specifies which condition occurred. Circuit topology and connectivity ■ Avoid using digital components, unless really necessary. Initialize the nodes with valid digital value to ensure no ambiguous state. These can cause time-step issues (time-step may unnecessary go too small) and hence transient convergence issue. ■ Use RC snubbers around diodes. ■ Add Capacitance for all semiconductor junctions (if no specific value is known: CJO=3pF for diodes, CJC & CJE=5pF for BJTs, CGS and CGD=5pF for JFETs and GaAsFETs, CGDO & CGSO=5pF for MOSFETs if no specific value is known). ■ Add realistic circuit and element parasitics.