Partial-power-down mode is a system function or capability if wanted to power off some part to conserve power. Because the system coordinates and controls the power-down or power-up sequence, typically the partial-power-down mode is required only to make sure that no circuit (either those that are powered on or those that are powered off) is damaged during the partial-power-off mode. This can be made sure if the circuits to be powered off have input and or output circuits that maintain a high-impedance state while Vcc = 0V.