The message:
Timestep too small
is not actually due to non-convergence. It means that, because of the nature of your circuit, to achieve the required accuracy, a time step smaller than the minimum permissible was needed. The default value for the minimum time step is 1e-18 or 1e-9*max-time-step whichever is the smaller. This error can be fixed by setting a lower value for the minimum time step and can be set in the user interface. See User's Manual/Analysis Modes/Transient Analysis/Setting up a Transient Analysis/Time Step.
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