Electronic system using a power regulator with reduced inrush current

1 . An electronic system, comprising:

a power regulator; and

an output capacitance device, coupled between the power regulator and a load;

wherein:

the output capacitance device comprises a first capacitor and a second capacitor;

when the power regulator is in a first power mode, the first capacitor and the second capacitor are both coupled to the power regulator;

when the power regulator is in a second power mode, which uses less power than the first power mode, the first capacitor is coupled to the power regulator, and the second capacitor is disconnected from the power regulator and is protected from being discharged by the power regulator; and

the power regulator comprises:

a first power MOS transistor, having a source terminal coupled to a power voltage, and a drain terminal coupled to the first capacitor through a first output terminal of the power regulator;

a second power MOS transistor, having a source terminal coupled to the power voltage, a gate terminal coupled to a gate terminal of the first power MOS transistor, and a drain terminal coupled to the second capacitor through a second output terminal of the power regulator;

wherein the second power MOS transistor is turned off while the power regulator operates in the second power mode.

2 . The electronic system as claimed in claim 1 , wherein:

the first power mode is a power-on mode; and

the second power mode is a power-off mode.

3 . The electronic system as claimed in claim 1 , wherein:

the first power mode is a normal-power mode of a dynamic voltage scaling function; and

the second power mode is a low-power mode of the dynamic voltage scaling function.

4 . The electronic system as claimed in claim 1 , further comprising:

a charge supplier, coupled to the second capacitor while the power regulator operates in the second power mode, to compensate for leakage from the second capacitor.

5 . The electronic system as claimed in claim 4 , further comprising:

a battery, providing power to the charge supplier to compensate for leakage of the second capacitor.

6 . The electronic system as claimed in claim 1 , wherein:

while the power regulator operates in the first power mode, the first capacitor and the second capacitor are both further coupled to the load; and

while the power regulator operates in the second power mode, the first capacitor is still coupled to the load, but the second capacitor is disconnected from the load.

7 . The electronic system as claimed in claim 1 , wherein:

while the power regulator operates in the first power mode, the first capacitor and the second capacitor are both further coupled to the load; and

while the power regulator operates in the second power mode, the first capacitor and the second capacitor are both kept coupled to the load.

8 . The electronic system as claimed in claim 1 , wherein the power regulator further comprises:

a first switch, coupled between the gate terminal of the first power MOS transistor and the gate terminal of the second power MOS transistor, wherein the first switch is closed while the power regulator operates in the first power mode, and is open while the power regulator operates in the second power mode; and

a second switch, which is closed while the power regulator operates in the second power mode to couple the gate terminal of the second power MOS transistor to the power voltage.

9 . The electronic system as claimed in claim 1 , wherein:

the load has a first power terminal coupled to the first output terminal of the power regulator, and a second power terminal coupled to the second output terminal of the power regulator.

10 . The electronic system as claimed in claim 9 , wherein the load further comprises:

circuitry, receiving power from the first power terminal and the second power terminal; and

a third switch, coupled between the second power terminal and the circuitry,

wherein:

while the power regulator operates in the first power mode, the third switch is closed; and

while the power regulator operates in the second power mode, the third switch is open.

11 . The electronic system as claimed in claim 1 , wherein the power regulator further comprises:

a charge supplier, powered by the power voltage,

wherein while the power regulator operates in the second power mode, the charge supplier is coupled to the second capacitor through the second output terminal of the power regulator to compensate for leakage from the second capacitor.

12 . The electronic system as claimed in claim 11 , further comprising:

a battery, providing the power voltage.

13 . The electronic system as claimed in claim 11 , wherein the charge supplier comprises:

a current source, driven by the power voltage to compensate for leakage from the second capacitor.

14 . The electronic system as claimed in claim 13 , wherein the charge supplier further comprises:

a fourth switch, turned on while the power regulator operates in the second power mode, to couple the current source to the second capacitor through the second output terminal of the power regulator; and

a comparator, generating a control signal to control the current source;

wherein the comparator has a first input terminal coupled to the second output terminal of the power regulator through the fourth switch, and a second input terminal biased at a reference voltage.

15 . The electronic system as claimed in claim 1 , wherein:

during a voltage-falling phase for switching from the first power mode to the second power mode, the second capacitor is changed to be disconnected from the power regulator.

16 . The electronic system as claimed in claim 15 , wherein:

during a voltage-rising phase for switching from the second power mode to the first power mode, the second capacitor is changed to be coupled to the power regulator.