# Patent

## Title
Switching-capacitor regulator with charge injection mode for high loading current

## Abstract

A switching-capacitor regulator with a charge injection mode for a high loading current is used to generate an output voltage at an output node, where the switching-capacitor regulator includes a storage capacitor, a switch module, a current source and a control unit. The switch module is coupled between the storage capacitor, a first supply voltage, a second supply voltage and the output node. The current source is coupled to the output node, and is used for selectively providing a current to the output node. The control unit is coupled to the switch module and the output node, and is used for controlling the switch module to selectively charge or discharge the storage capacitor, and for controlling the current source to selectively provide the current to the output node, to adjust a voltage level of the output voltage.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching-capacitor regulator, and more particularly, to a switching-capacitor regulator that is able to provide a stable output voltage under over-loading current.
2. Description of the Prior Art
In a conventional switching-capacitor regulator, if a loading current exceeds a maximum current that a system can provide, an output voltage of the switching-capacitor regulator will have a great voltage drop, causing that the switching-capacitor regulator cannot provide a stable output voltage. In addition, due to the drop of the output voltage, an allowable value of the loading current is also decreased, causing unstable operations of elements of the system.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide a switching-capacitor regulator that is able to provide a stable output voltage under over-loading current, to solve the above-mentioned problem.
According to one embodiment of the present invention, a switching-capacitor regulator with a charge injection mode for a high loading current is provided, where the switching-capacitor regulator is used to generate an output voltage at an output node, and the switching-capacitor regulator comprises a storage capacitor, a switch module, a current source and a control unit. The switch module is coupled between the storage capacitor, a first supply voltage, a second supply voltage and the output node. The current source is coupled to the output node, and is used for selectively providing a current to the output node. The control unit is coupled to the switch module and the output node, and is used for controlling the switch module to selectively charge or discharge the storage capacitor, and for controlling the current source to selectively provide the current to the output node, to adjust a voltage level of the output voltage.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating a switching-capacitor regulator according to one embodiment of the present invention.
FIG. 2 (a)-(c) are diagrams illustrating charging/discharging the storage capacitor and charging the output node when an output voltage of the switching-capacitor regulator is within different ranges.
FIG. 3 shows a variation of the output voltage of the switching-capacitor regulator when the loading current exceeds a maximum loading current that a system can provide.



DETAILED DESCRIPTION
Certain terms are used throughout the description and following claims to refer to particular components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following description and in the claims, the terms “include” and “comprise” are used in an open-ended fashion, and thus should be interpreted to mean “include, but not limited to . . . ”. Also, the term “couple” is intended to mean either an indirect or direct electrical connection. Accordingly, if one device is coupled to another device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections.
Please refer to FIG. 1, which is a diagram illustrating a switching-capacitor regulator 100 according to one embodiment of the present invention, where the switching-capacitor regulator 100 is used to generate a stable output voltage Vout at an output node Nout, and the output node Nout is connected to a load (FIG. 1 shows a loading capacitor Cload and a loading current Iload). As shown in FIG. 1, the switching-capacitor regulator 100 comprises a storage capacitor Cs, a switch module 110, a current source (in this embodiment, the current source is implemented by a transistor M1) and a control unit 120, where the switch module 110 comprises four switches SW1, SW2, SW3 and SW4, the switch SW1 is coupled to a supply voltage VDD and a first node of the storage capacitor Cs, and the switch SW1 is used to selectively connect the supply voltage VDD to the first node of the storage capacitor Cs; the switch SW2 is coupled between the first node of the storage capacitor Cs and the output node Nout, and the switch SW2 is used to selectively connect the first node of the storage capacitor Cs to the output node Nout; the switch SW3 is coupled between a second node of the storage capacitor Cs and the output node Nout, and the switch SW3 is used to selectively connect the second node of the storage capacitor Cs to the output node Nout; the switch SW4 is coupled to another supply voltage (in this embodiment, it is a ground voltage GND) and the second node of the storage capacitor Cs, and the switch SW4 is used to selectively connect the ground voltage GND to the second node of the storage capacitor Cs. In addition, the control unit 120 comprises a bandgap voltage generating circuit 122, a first comparator 124, a second comparator 126, a first control signal generating unit 128 and a second control signal generating unit 129, and the control unit 120 generates a plurality of first control signals VC1_1 and VC1_2 and a second control signal VC2 to control the operations of the switch module 110 and the transistor M1, respectively.
In the operations of the switching-capacitor regulator 100, by enabling or disabling the switches SW1-SW4 to charge or discharge the storage capacitor Cs, and by enabling or disabling the transistor M1 to selectively charge the node Nout, the output voltage Vout can be kept at a stable level. In detail, the control unit 120 can enable or disable the switches SW1-SW4 to charge or discharge the storage capacitor Cs according to a level of the output voltage Vout, to maintain a stable output voltage Vout. However, when the loading current Iload is too high to make the output voltage Vout be kept at a stable value, the control unit 120 will enable the transistor M1 to make the transistor serve as another current source to charge the output node Nout to increase the level of the output voltage Vout. The detailed operations of each element of the switching-capacitor regulator 100 are described as follows.
The bandgap voltage generating circuit 122 generates two reference voltages VREF1 and VREF2, where the reference voltage VREF1 is an ideal value of the output voltage Vout, and the reference voltage VREF2 is slightly lower than the reference VREF1. For example, assuming that the supply voltage VDD is 3.3V and the reference voltage VREF1 is 1.2V, the reference voltage VREF2 can be 1.0V or 1.1V.
Then, the first comparator 124 compares the output voltage Vout and the reference voltage VREF1 to generate a comparison result CP1, and the first control signal generating unit 128 generates the first control signals VC1_1 and VC1_2 to enable or disable the switches SW1-SW4 according to the comparison result CP1, where the first control signals VC1_1 and VC1_2 are out of phase (i.e., with opposite phases). In addition, the second comparator 126 compares the output voltage Vout and the reference voltage VREF2 to generate a comparison result CP2, and the second control signal generating unit 129 generates the second control signal VC2 to enable or disable the transistor M1 according to the comparison result CP2.
In detail, when the output voltage Vout is greater than the reference voltage VREF1, the first control signal generating unit 128 generates the first control signals VC1_1 and VC1_2 to disable the switches SW1-SW4 to slowly discharge the output node Nout, to make the output voltage Vout be kept at a level of the reference voltage VREF1. In addition, the second control signal generating unit 129 generates the second control signal VC2 to disable the transistor M1.
When the output voltage Vout is lower than the reference voltage VREF1, the first control signal generating unit 128 generates the first control signals VC1_1 and VC1_2, each of the first control signals has two phases periodically, to alternately charge and discharge the storage capacitor Cs to make the output voltage Vout be kept at the level of the reference voltage VREF1. In detail, when it is to charge the storage capacitor Cs, the first control signal VC1_1 will enable the switches SW1 and SW3, and the first control signal VC1_2 will disable the switches SW2 and SW4, to charge the storage capacitor Cs and provide a current to the output node Nout, where FIG. 2 (b) shows the equivalent circuit when storage capacitor Cs is charged. In addition, when the it is to discharge the storage capacitor Cs, the first control signal VC1_2 will enable the switches SW2 and SW4, and the first control signal VC1_1 will disable the switches SW1 and SW3, to discharge the storage capacitor Cs, where FIG. 2 (a) shows the equivalent circuit when storage capacitor Cs is discharged. In addition, if the output voltage Vout is greater than the reference voltage VREF2, the second control signal generating unit 129 will generate the second control signal VC2 to disable the transistor M1.
In addition, when the output voltage Vout is lower than the reference voltage VREF2, it is meant that the loading current Iload is over high, causing that the output voltage Vout continues dropping and may not be kept at a stable value. At this time, the first control signal generating unit 128 continues to generate the first control signals VC1_1 and VC1_2 each has two phases periodically to make the storage capacitor Cs continues to charge the output node Nout, and the second control signal generating unit 129 generates the second control signal VC2 to enable the transistor M1 to make the transistor M1 serve as a current source I to charge the output node Nout to increase the level of the output voltage Vout. FIG. 2(c) shows the equivalent circuit when the transistor M1 charges the output node Nout.
In light of above, because when the loading current Iload is over-high, the transistor M1 will provide another charging path to charge the output node Nout to increase the level of the output voltage Vout, therefore, even the loading current Iload exceeds a maximum loading current Iload_max provided by the system, the output voltage Vout is merely slightly decreased, as shown in FIG. 3, and the operations of the system will not be influenced, where FIG. 3 shows a variation of the output voltage of the switching-capacitor regulator 100 when the loading current exceeds a maximum loading current that a system can provide.
In addition, the detailed circuit designs such as the switch module 120 comprising four switches SW1-SW4 and using the transistor M1 to implement the current source are for illustrative purposes only, and are not limitations of the present invention. In other embodiments of the present invention, because the switching-capacitor regulator has several different circuit structures, and the switch module 120 may be a combined circuit of a plurality of switches and several storage capacitors, as long as when the output voltage Vout of the switching-capacitor regulator is lower than the reference voltage VREF2, the output node Nout has an equivalent circuit shown in FIG. 2(c), the quantity of the switches of the switch module 120 and their coupling method can be designed by designer's consideration, and the transistor M1 can also be replaced by another current source. These alternative designs shall fall within the scope of the present invention.
Briefly summarized, in the switching-capacitor regulator of the present invention, when the output voltage of the switching-capacitor regulator is lower than a reference voltage due to an over-loading current, the switching-capacitor regulator can provide two current paths to charge the output node to make the output voltage be kept at a stable value. Therefore, the operations of the elements of the system will not be influenced.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

## Claims

1. A switching-capacitor regulator with a charge injection mode for a high loading current, wherein the switching-capacitor regulator generates an output voltage at an output node, comprising:
a storage capacitor;
a switch module, coupled between the storage capacitor, a first supply voltage, a second supply voltage and the output node, and the switch module comprises:
a first switch, coupled to a first node of the storage capacitor, for selectively connecting the first supply voltage to the first node of the storage capacitor;
a second switch, coupled between the first node of the storage capacitor and the output node, for selectively connecting the first node of the storage capacitor to the output node;
a third switch, coupled between a second node of the storage capacitor and the output node, for selectively connecting the second node of the storage capacitor to the output node; and
a fourth switch, coupled to the second node of the storage capacitor, for selectively connecting the second supply voltage to the second node of the storage capacitor;

a current source, directly connected to the output node, for selectively providing a current to the output node directly; and
a control unit, coupled to the switch module and the output node, for controlling the switch module to selectively charge or discharge the storage capacitor, and for controlling the current source to selectively provide the current to the output node, to adjust a voltage level of the output voltage;
wherein the control unit controls the switch module to selectively charge or discharge the storage capacitor, and controls the current source to selectively provide the current to the output node directly to adjust the voltage level of the output voltage according to the voltage level of the output voltage, and the control unit comprises:
a first comparator, for comparing the output voltage and a first reference voltage to generate a first comparison result;
a first control signal generating unit, coupled to the first comparator, for generating a plurality of first control signals to control the switch module according to the first comparison result;
a second comparator, for comparing the output voltage and a second reference voltage to generate a second comparison result; and
a second control signal generating unit, coupled to the second comparator, for generating a second control signal to control the current source according to the second comparison result;
wherein the second reference voltage is lower than the first reference voltage; and when the output voltage is greater than the first reference voltage, the first control signal generating unit generates the first control signals to disable all of the first switch, the second switch, the third switch and the fourth switch, and the second control signal generating unit generates the second control signal to disable the current source; when the output voltage is lower than the first reference voltage and is greater than the second reference voltage, the first control signal generating unit generates the first control signals to control the first switch, the second switch, the third switch and the fourth switch to alternately charge and discharge the storage capacitor, and the second control signal generating unit generates the second control signal to disable the current source; and when the output voltage is lower than the second reference voltage, the first control signal generating unit generates the first control signals to control the first switch, the second switch, the third switch and the fourth switch to alternately charge and discharge the storage capacitor, and the second control signal generating unit generates the second control signal to enable the current source.

2. The switching-capacitor regulator of claim 1, wherein the current source is a switch coupled between the first supply voltage and the output node, and is utilized for selectively connecting the first supply voltage directly to the output node, without through the switch module.

3. The switching-capacitor regulator of claim 1, wherein the current source is a switch coupled between the first supply voltage and the output node, and is utilized for selectively connecting the first supply voltage directly to the output node according to the second control signal, without through the switch module.

4. The switching-capacitor regulator of claim 3, wherein when the output voltage is lower than the second reference voltage, the second control signal generating unit controls the current source to provide the current to the output node directly; and when the output voltage is greater than the second reference voltage, the second control signal generating unit controls the current source to not provide the current to the output node.

5. The switching-capacitor regulator of claim 1, wherein the first reference voltage and the second reference voltage are generated by a bandgap voltage generating circuit.