Patent ID: 8456140

Claim:
A power control apparatus for controlling a supply voltage for an associated circuit, comprising: a power input for receiving an input voltage; a power output for supplying said supply voltage to said associated circuit; a switch device comprising a first terminal coupled to said power input, a second terminal coupled to said power output, and a control terminal for receiving a sleep select signal; a control device for selectively connecting said second terminal of said switch device to said control terminal of said switch device, wherein when said second terminal and said control terminal are not connected by said control device, said switch device is responsive to said sleep select signal to select whether or not to supply said input voltage to said power output; and when said second terminal and said control terminal are connected by said control device, a voltage difference is formed between said power input and said power output and said switch device supplies a retention voltage to said power output, said retention voltage being different to said input voltage; and a tristate buffer coupled to said control terminal of said switch device and configured to: isolate said control terminal of said switch device from said sleep select signal when said second terminal is connected to said control terminal by said control device; and allow said sleep select signal to be supplied to said control terminal of said switch device when said second terminal is not connected to said control terminal by said control device.