Disclosed is a voltage monitoring circuit for use in detecting if a voltage supplied to current-generating circuit is sufficient to allow the current-generating circuit to produce a desired current. In one embodiment the circuit is designed for use in an implantable device that is configured to deliver therapeutic pulses to a patient. The voltage monitoring circuit is configured to produce a signal if a supplied voltage is insufficient to allow a current-generating circuit to deliver a requested current to a set of electrodes. In one embodiment, the voltage monitoring circuit detects a change in a difference between the voltage at a node in the current-generating circuit and the supplied voltage.