The present invention relates to a semiconductor integrated circuit, in particular to a technology useful for setting the value of rush current flowing in the power switch circuit at the time of turning “on” the power supply with a high precision.
The leak current per transistor is increasing and the number of on-chip transistors is also increasing due to the transistor-size scaling of semiconductor integrated circuits such as CMOS digital LSI. This increases the standby power of the whole chip to a very serious level.
As described in the document: A. Fahim, “Low-leakage current, low-area voltage, regulator for system-on-chip processors”, ELECTRONICS LETTERS. 15th Sep. 2005, VOL. 41, NO. 19., generally a P-channel MOS transistor playing the role of a switch between the power supply and the microprocessor is used in order to reduce the standby consumption power. In the disabled state that shut off the microprocessor, the leak power serves as the cutoff current of the P-channel MOS transistors.
On the other hand, the method proposed in the Japanese Unexamined Patent Publication No. 2003-330555 describes the following technology. The stabilizing power circuit mounted on a semiconductor integrated circuit includes an output control MOS transistor for outputting an internal source voltage from an external source voltage inputted therein and an error amplifier for comparing the feedback voltage from the internal source voltage and the reference voltage and for controlling the gate of the output control MOS transistor. When the power supply is turned “on”, the stabilizing power circuit for normal operation does not enter into operation, but a start-up circuit including a diode-connected MOS transistor with drain gate short-circuited, a switch for operating this diode-connected MOS transistor and the output control MOS transistor as current mirrors and a time constant circuit enters into operation. After the power is turned “on”, the switch is on during a time constant period of time determined by the resistances and capacitors of the time constant circuit, and the drain gate short-circuited and diode-connected MOS transistor and the output control MOS transistor work as current mirrors. Therefore, during the time-constant period of time, the current of the output control MOS transistor is limited to the current value determined by the mirror ratio of the current mirror. This limitation of current limits excessive rush current at the time of turning “on” the power supply. After the time constant length of time has passed, the switch is turned “off”, and the output control MOS transistor is controlled by the output of the error amplifier, and the stabilizing power circuit starts operating normally.