Issue link: https://resources.pcb.cadence.com/i/1180526
PSpice A/D User Guide Convergence and "time step too small errors" October 2019 855 Product Version 17.4-2019 © 2022 All Rights Reserved. Source limits: Another consideration is that the controlled sources must turn off when the supplies are almost 0 (.001%). There is special code in PSpice A/D which "squelches" the controlled sources in a continuous way near 0 supplies. However, care should still be taken using expressions that have denominators. Take, for example, a constant power load: GLOAD 3, 5 VALUE = {2Watts/V(3,5)} The first repeating series starts with V(3,5) = 0 and the current through GLOAD would be infinite (actually, the code in PSpice A/D which does the division clips the result to a finite value). The "squelching" code is required to be a smooth and well-behaved function. Note: The "squelching" code cannot be "strong" enough to suppress dividing by 0. The result is that GLOAD does not turn off near 0 power supplies. A better way is described in the application note Modeling Constant Power Loads. The "squelching" code is sufficient for turning off all expressions except those having denominators. In general, though, it is good practice to constrain expressions having the LIMIT function to keep results within physically realistic bounds. Example: A first approximation to an OPAMP that has an open loop gain of 100,000 is: VOPAMP 3, 5 VALUE = {V(in+,in-)*1e5} This has the undesirable property that there is no limit on the output. A better expression is: VOPAMP 3, 5 VALUE = + {LIMIT(V(in+,in-)*1e5,15v,-15v} where the output is limited to +/- 15 volts. ■ Unguarded p-n junctions A second consideration is to avoid "unguarded" p-n junctions (no series resistance). ■ No leakage resistance A third consideration is to avoid situations, which could have an ideal current source pushing current into a reverse-biased p-n junction without a shunt resistance. p-n junctions in PSpice A/D