A memory controller includes an interface and a processor. The interface is configured to communicate with one or more memory devices that require an operation voltage. The memory devices are capable of obtaining the operation voltage either from a power supply external to the memory device or from respective charge pumps internal to the memory devices. The processor is configured to predict storage activity in the memory devices, and to cause the memory devices to select a source for the operation voltage between the power supply and the respective charge pumps in accordance with the predicted storage activity.