If your drives move the correct distance, then you have the counts
per unit configured correctly for your Encoder and G320 setup.
If the fault only occurs sometimes, you may have a tuning problem.
Try running with lower velocity. If this cures the problem, it is likely
a tuning problem.
The charge pump is required if you are using the PMDX-126 to
interface with the Err/RST terminal of the G320 drivers. If you are
manually resetting the drives and have not connection from the
Err/RST terminal to the PMDX-126, then a charge pump is not
required.