In a non-volatile memory system (20), when it is discovered that the voltage pump pulse provided by a charge pump (32) for programming the memory cells does not match a reference voltage, the programming time period of the voltage pump pulse is adjusted to a value that remains substantially unchanged until the end of the programming cycle. In this manner, the fluctuation in the effective programming time period of the programming pulses is prevented for the remainder of the programming cycle so that a broadening of the threshold voltage distribution will not occur or will be reduced. This feature allows a short programming time period to be designated for the programming pulses for enhanced performance, while allowing the flexibility of increased program time period when the charge pump is operating under conditions that causes it to be slow and/or weak.