| 摘要 |
PURPOSE: A power supply for a CPU is provided to prevent an efficiency of a CPU from being deteriorated although the CPU is operated at a low activity state. CONSTITUTION: A CPU power state information signal being output from a south-bridge controller(116) is inverted through an inverter(INV1) and inputted to an enable terminal(EN) of a DC/DC converter(151). If a signal being output from the inverter(INV1) is a high-level(that is, the information signal is low-level), the DC/DC converter(151) converts a voltage(for example, 3.3V) being supplied from a main power supply(160) into a normal voltage(for example, 1.15-1.05V) and outputs the voltage. If a signal being output from the inverter(INV1) is a low-level(that is, the information signal is high-level), the DC/DC converter(151) does not perform a DC/DC converting operation. An LDO(Low Dropout) circuit(152) includes an input terminal(IN) which receives a voltage(VLDO) being output from the main power supply(160), a shut down input terminal(/SHDN) which receives the information signal being output from the south-bridge controller(116), and an output terminal.
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