Protection Circuit and Its Operating Method

Abstract

The present invention provides a protection circuit and an operation method thereof, which are applicable to a switched-capacitor voltage regulator circuit having a capacitor. The protection circuit includes a current source, a first switch circuit, a second switch circuit, and a control unit. The control unit controls the second switch circuit to conduct so that the top and bottom ends of the capacitor are electrically connected, and controls the first switch circuit to disconnect the current source from the capacitor and sets the voltages of the top and bottom ends to a default high voltage. Then, the control unit controls the second switch circuit to disconnect the top and bottom ends from being electrically connected, and controls the first switch circuit to conduct so that a current flows out from the bottom end of the capacitor. When the voltage difference between the top and bottom ends is equal to the default initial voltage, the control unit controls the first switch circuit to disconnect the current source from being electrically connected to the capacitor; then, the control unit controls the current flowing into or out of the top end of the capacitor according to the voltage of the top end of the capacitor to avoid generating inrush current.

Description

Technical Field

[0001] The present invention relates to a protection circuit, and more particularly to a protection circuit applicable to a switched-capacitor voltage regulator circuit. Background Art

[0002] In recent years, switched-capacitor voltage regulator circuits have the advantage of high conversion efficiency, so more and more chips use switched-capacitor voltage regulator circuits. When a switched-capacitor voltage regulator circuit starts to operate, an initial voltage is required across the capacitor. For example, a three-level buck converter requires the initial voltage across its flying capacitor to be half of the input voltage.

[0003] In order to reduce the on-resistance, most switched-capacitor voltage regulator circuits, such as three-level buck converters, use low-voltage components. However, this design requires the initial voltage across the capacitor to be precise, otherwise it may burn out the low-voltage components and cause chip damage. In order to have an initial voltage across the capacitor when the switched-capacitor voltage regulator circuit is powered on, the switched-capacitor voltage regulator circuit may have to provide a large current to charge the capacitor in the initial stage, but this operation is likely to generate inrush current and damage the chip.

[0004] In addition, in order to reduce costs, the transistors used as switching components in the switched-capacitor voltage regulator circuit are designed according to the voltage across them during actual operation. Therefore, when the voltage across the capacitor in the switched-capacitor voltage regulator circuit changes greatly, it is easy for the transistors to bear too large a voltage across them and burn out. Summary of the Invention

[0005] An object of the present invention is to provide a protection circuit to solve the above-mentioned known technical problems.

[0006] To achieve the above object, the present invention provides a protection circuit applicable to a switched-capacitor voltage regulator circuit, which includes a capacitor. The protection circuit includes: a current source having a current input terminal and a current output terminal; a first switch circuit selectively electrically connecting the current source to one of a top end and a bottom end of the capacitor; a second switch circuit connected in parallel with the top end and the bottom end of the capacitor; and a control unit. In a first operation stage, the control unit controls the second switch circuit to conduct and controls the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor, so that the top end and the bottom end of the capacitor are electrically connected and the control unit sets the voltages of the top end and the bottom end of the capacitor to a default high voltage. In a second operation stage, the control unit controls the second switch circuit to cut off, so that the top end and the bottom end of the capacitor are not electrically connected, and controls the first switch circuit to conduct to electrically connect the current input terminal of the current source to the bottom end of the capacitor. When a voltage difference between the top end and the bottom end of the capacitor is equal to a default initial voltage, the control unit enters a third operation stage. In the third operation stage, the control unit controls the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor, and then selectively electrically connects one of the current input terminal and the current output terminal of the current source to the top end of the capacitor according to the voltage of the top end of the capacitor.

[0007] According to an embodiment, the switched-capacitor voltage regulator circuit receives an input voltage, and the default initial voltage is half of the input voltage.

[0008] According to an embodiment, in the first operation stage, when the input voltage is gradually rising, the control unit determines whether the voltage of the top end of the capacitor is higher than or equal to the default high voltage to decide whether to enter the second operation stage.

[0009] According to an embodiment, in the third operation stage, when the control unit determines that the voltage of the top end of the capacitor is higher than a first threshold voltage, the control unit controls the first switch circuit to electrically connect the current input terminal of the current source to the top end of the capacitor.

[0010] According to an embodiment, in the third operation stage, when the control unit determines that the voltage of the top end of the capacitor is lower than a second threshold voltage, the control unit controls the second switch circuit to electrically connect the current output terminal of the current source to the top end of the capacitor.

[0011] According to an embodiment, the first threshold voltage is higher than the second threshold voltage.

[0012] To achieve the above object, the present invention further provides an operating method for a protection circuit, the protection circuit being applicable to a switched-capacitor voltage regulator circuit, the switched-capacitor voltage regulator circuit including a capacitor, and the protection circuit including a current source, a first switching circuit, and a second switching circuit. The operating method includes the following steps: controlling the second switching circuit to conduct, so that the top end and the bottom end of the capacitor are electrically connected, and controlling the first switching circuit to disconnect the current source from the top end and the bottom end of the capacitor, and setting the voltages of the top end and the bottom end of the capacitor to a default high voltage; when the voltages of the top end and the bottom end of the capacitor are equal to the default high voltage, controlling the second switching circuit to cut off, so that the top end and the bottom end of the capacitor are not electrically connected, and controlling the first switching circuit to connect the current input end of the current source to the bottom end of the capacitor; when a voltage difference between the top end and the bottom end of the capacitor is equal to a default initial voltage, controlling the first switching circuit to disconnect the current source from the top end and the bottom end of the capacitor; controlling the first switching circuit to selectively connect one of the current input end and the current output end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor.

[0013] According to an embodiment, the step of controlling the first switching circuit to selectively connect one of the current input end and the current output end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor further includes: when the voltage at the top end of the capacitor is higher than a first threshold voltage, controlling the first switching circuit to connect the current input end of the current source to the top end of the capacitor.

[0014] According to an embodiment, the step of controlling the first switching circuit to selectively connect one of the current input end and the current output end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor further includes: when the voltage at the top end of the capacitor is lower than a second threshold voltage, controlling the second switching circuit to connect the current output end of the current source to the top end of the capacitor.

[0015] According to an embodiment, the first threshold voltage is higher than the second threshold voltage. Description of the Drawings

[0016] Figure 1 is a block diagram of a protection circuit of the present invention.

[0017] Figure 2 is a block diagram of an embodiment of a protection circuit of the present invention.

[0018] Figure 3 is a flowchart of an operating method of a protection circuit of the present invention. Detailed Description of the Invention

[0019] The embodiments of the present invention will be described in detail below in conjunction with the drawings and embodiments, so as to fully understand how the present invention uses technical means to solve technical problems and achieve the implementation process of technical effects and implement accordingly.

[0020] Please refer to Figure 1 , which is a block diagram of a protection circuit of the present invention. As Figure 1 shown, the protection circuit of the present invention is applicable to a switched-capacitor voltage regulator circuit 10, such as a three-level buck converter. The switched-capacitor voltage regulator circuit 10 includes a capacitor CF, and the protection circuit is used to initialize a voltage difference between a top end CFP and a bottom end CFN of the capacitor CF to a default initial voltage, and to control the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF during operation. The default initial voltage is, for example, half of the input voltage or supply voltage. The protection circuit may include a current source 21, a first switch circuit 22, a second switch circuit 23, and a control unit 24.

[0021] The first switch circuit 22 is used to selectively electrically connect the current source 21 to one of the top end CFP and the bottom end CFN of the capacitor CF. In one embodiment, the first switch circuit 22 includes at least a plurality of switches. The second switch circuit 23 is connected in parallel with the top end CFP and the bottom end CFN of the capacitor CF. Its detailed connection method and operation method will be described in subsequent paragraphs.

[0022] The control unit 24 has at least three operating phases, including a first operating phase, a second operating phase, and a third operating phase. In the first operating phase, the control unit 24 controls the second switch circuit 23 to conduct, so that the top end CFP and the bottom end CFN of the capacitor CF are electrically connected; and the control unit 24 controls the first switch circuit 22 to disconnect the current source 21 from the top end CFP and the bottom end CFN of the capacitor CF, whereby the control unit 24 sets the voltages of the top end CFP and the bottom end CFN of the capacitor CF to a default high voltage. Since the top end CFP and the bottom end CFN are electrically connected, other components of the protection circuit 20 cannot detect the existence of the capacitor CF, which means that the protection circuit 20 can quickly change the voltages of the top end CFP and the bottom end CFN without being affected by the capacitor CF; for example, the protection circuit 20 can increase the voltages of the top end CFP and the bottom end CFN at a speed of 3.6V / 1uS, and a large current is not required to charge the capacitor CF during the voltage increase process, thereby avoiding the generation of inrush current.

[0023] In the second operation stage, the control unit 24 controls the second switch circuit 23 to be turned off, so that the top end CFP and the bottom end CFN of the capacitor CF are not electrically connected, and controls the first switch circuit 22 to be turned on so that the current input end of the current source 21 is electrically connected to the bottom end CFN of the capacitor CF, thereby generating a current flowing out from the bottom end CFN of the capacitor CF until the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF is equal to the default initial voltage.

[0024] When the current flows out from the bottom end CFN of the capacitor CF, the voltage of the bottom end CFN of the capacitor CF will gradually decrease. In addition, when the current flows out from the bottom end CFN of the capacitor CF, as long as there is also a current flowing into the top end CFP of the capacitor CF, the voltage of the top end CFP of the capacitor CF can be maintained at the default high voltage formed in the first operation stage. In the second operation stage, the voltage of the top end CFP of the capacitor CF is maintained at the default high voltage formed in the first operation stage, while the voltage of the bottom end CFN of the capacitor CF will gradually decrease. When the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF is equal to the default initial voltage, the control unit 24 enters the third operation stage.

[0025] In the third operation stage, the control unit 24 controls the first switch circuit 22 to disconnect the current source from the top end CFP and the bottom end CFN of the capacitor CF, and the switching capacitor voltage stabilizing circuit 10 can start to operate when the voltage across the capacitor CF is the default initial voltage. For example, when the voltage of the bottom end CFN of the capacitor CF drops to the default low voltage, such as 0V, the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF is equal to the default initial voltage (which is the difference between the default high voltage and the default low voltage), which means that the switching capacitor voltage stabilizing circuit 10 can start to operate. Therefore, the control unit 24 controls the first switch circuit 22 to disconnect the electrical connection between the current input end of the current source 21 and the bottom end CFN of the capacitor CF, so that the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF is the default initial voltage.

[0026] According to the above content, the protection circuit of the present invention can quickly increase the voltage of the top end CFP of the capacitor CF, and does not need to use a large current to charge the capacitor CF during the voltage increase process, thereby avoiding the generation of inrush current and achieving the effect of circuit protection.

[0027] Next, the control unit 24 controls the first switch circuit 22 according to the voltage VCFP at the top CFP of the capacitor CF to electrically connect one of the current inflow end and the current outflow end of the current source 21 to the top CFP of the capacitor CF. For example, when the bottom CFN of the capacitor CF is grounded, when the voltage VCFP is higher than the first threshold voltage, the control unit 24 electrically connects the current inflow end of the current source 21 to the top CFP of the capacitor CF to decrease the voltage VCFP; when the voltage VCFP is lower than the second threshold voltage, the control unit 24 electrically connects the current outflow end of the current source 21 to the top CFP of the capacitor CF to increase the voltage VCFP. Thus, the voltage difference between the top CFP and the bottom CFN of the capacitor CF can be maintained at the default initial voltage to protect the low-voltage components connected to the capacitor CF.

[0028] Please refer to Figure 2 , which is a block diagram of an embodiment of a protection circuit according to the present invention. As shown in the embodiment of Figure 2 , the protection circuit may include a current source 21, switches 221 to 225, a switch 231, and a control unit 34; in this embodiment, the protection circuit is applied to a third-order buck converter 11. The third-order buck converter 11 includes transistors Q1 to Q4 and a capacitor CF. The transistors Q1 to Q4 are connected in series in sequence. The source of the transistor Q1 receives the supply voltage VIN, and the source of the transistor Q4 is grounded. The gates of the transistors Q1 to Q4 receive control signals to enter the conducting state or the cutoff state respectively. The top CFP and the bottom CFN of the capacitor CF are respectively coupled to the drain of the transistor Q and the drain of the transistor Q4. The transistors Q1 to Q4 are implemented with low-voltage components; the switches 221 to 225 implement Figure 1 the first switch circuit 22 shown in Figure 1 , and the switch 231 implements

[0029] the second switch circuit 23 shown in

[0030] The switch 231 is connected in parallel with the top CFP and the bottom CFN of the capacitor CF. The switch 221 is connected between the current inflow end of the current source 21 and the switch 231; one end of the switch 224 is connected to the current inflow end of the current source 21, and the other end receives the supply voltage VIN; one end of the switch 223 is the current outflow end of the current source 21, and the other end is grounded; the switch 222 is connected between the top CFP of the capacitor CF and the current inflow end of the current source 21; one end of the switch 225 is connected to the current outflow end of the current source 21, and the other end is connected to the top CFP of the capacitor CF.

[0030] The control unit 34 can be used to control the switches 221 to 225 and the switch 231 to be in the conducting or cutoff state; in this embodiment, the control unit 34 further includes a voltage setting unit 35.

[0031] In the first operation stage, the control unit 34 controls the switch 231 to conduct, so that the top end CFP and the bottom end CFN of the capacitor CF are electrically connected to each other, and the voltage setting unit 35 is used to set the voltages of the top end CFP and the bottom end CFN of the capacitor CF to the default high voltage; in addition, the control unit 34 controls the switches 221, 222, and 225 to cut off, so that the current source 21 is not electrically connected to the top end CFP and the bottom end CFN of the capacitor CF.

[0032] Since the supply voltage VIN is relatively unstable or takes some time to rise to the default value when the system is just powered on, and the default high voltage is affected by the stability of the supply voltage VIN, the control unit 34 can further determine whether the voltage of the top end CFP of the capacitor CF is higher than or equal to the default high voltage. If so, the control unit 34 enters the second operation stage.

[0033] In the second operation stage, the control unit 34 controls the switch 231 to cut off, so that the top end CFP and the bottom end CFN of the capacitor CF are not electrically connected. At this time, the voltage VCFP of the top end CFP and the voltage VCFN of the bottom end CFN are both the default high voltage; the control unit 34 controls the switches 221 and 223 to conduct and controls the switches 222, 224, and 225 to cut off, so that the bottom end CFN of the capacitor CF is electrically connected to the current inflow end of the current source 21, thereby allowing current to flow out from the bottom end CFN of the capacitor CF, causing the voltage VCFN of the bottom end CFN of the capacitor CF to drop, and increasing the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF. When a voltage difference between the top end CFP and the bottom end CFN of the capacitor is equal to the default initial voltage, the control unit 34 enters the third operation stage.

[0034] In the third operation stage, the control unit 34 first controls the switches 231, 221 - 225 to cut off and enables the three - order buck converter 11 to start operating; then, when the three - order buck converter 11 is operating, the control unit 34 controls the switches 221 - 225 according to the voltage VCFP of the top end CFP of the capacitor CF, so that one of the current inflow end and the current outflow end of the current source 21 is selectively electrically connected to the top end CFP, in order to maintain the voltage across the top end CFP and the bottom end CFN of the capacitor CF and prevent the low - voltage components (such as transistors Q1 - Q4) of the three - order buck converter 11 from being damaged due to the unstable voltage across the capacitor CF.

[0035] When the transistor Q4 is turned on and the bottom end CFN of the capacitor CF is grounded, when the voltage VCFP is higher than the first threshold voltage, the control unit 34 turns on the switches 222 and 223 and turns off the switches 221, 224 and 225, so that the current of the current source 21 flows into the top end CFP of the capacitor CF, causing the voltage VCFP to drop; when the voltage VCFP is lower than the second threshold voltage, the control unit 34 electrically connects the current output end of the current source 21 to the top end CFP of the capacitor CF to increase the voltage VCFP. Thus, the voltage difference between the top end CFP and the bottom end CFN of the capacitor CF can be maintained at the default initial voltage to protect the switching components connected to the capacitor CF. The first threshold voltage is higher than the second threshold voltage.

[0036] In an embodiment, when the comparator is used for the above voltage comparison, the first threshold voltage can be the default initial voltage plus the hysteresis voltage of the comparator, and the second threshold voltage can be the default initial voltage minus the hysteresis voltage of the comparator.

[0037] Please refer to Figure 3 , which is a flowchart of an operation method of a protection circuit of the present invention. This operation method can be applied to Figure 1 the protection circuit shown, including steps S71 to S74.

[0038] In step S71, control the second switch circuit to turn on, electrically connect the top end and the bottom end of the capacitor of the switched-capacitor voltage regulator circuit, control the first switch circuit to electrically disconnect the current source from the top end and the bottom end of the capacitor, and set the voltages of the top end and the bottom end of the capacitor to a default high voltage.

[0039] Since the top end and the bottom end of the capacitor are electrically connected, external components cannot detect the existence of the capacitor of the switched-capacitor voltage regulator circuit, so the voltages of the top end and the bottom end can be set and quickly pulled up without being affected by the capacitor CF. Moreover, a large current is not required to charge the capacitor during the voltage boosting process, thus avoiding the generation of inrush current.

[0040] In step S72, when the voltages of the top end and the bottom end of the capacitor are equal to the default high voltage, control the second switch circuit to turn off, electrically disconnect the top end and the bottom end of the capacitor, and control the first switch circuit to electrically connect the current input end of the current source to the bottom end of the capacitor.

[0041] In step S73, when a voltage difference between the top end and the bottom end of the capacitor is equal to a default initial voltage, control the first switch circuit to electrically disconnect the current source from the top end and the bottom end of the capacitor. At the same time, the switched-capacitor voltage regulator circuit can start to operate.

[0042] In step S74, the first switching circuit is controlled according to the voltage at the top of the capacitor to selectively electrically connect one of the current inflow end and the current outflow end of the current source to the top of the capacitor. For example, when the bottom of the capacitor is grounded, when the voltage at the top of the capacitor is higher than the first threshold voltage, the control unit electrically connects the current inflow end of the current source to the top of the capacitor to lower the voltage; when the voltage is lower than the second threshold voltage, the control unit electrically connects the current outflow end of the current source to the top of the capacitor to raise the voltage. Thus, the voltage difference between the top and the bottom of the capacitor can be maintained at the default initial voltage to protect the low-voltage components connected to the capacitor CF.

[0043] Although the present invention has been disclosed as above in the foregoing embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of patent protection of the present invention shall be subject to that defined by the claims attached to this specification.

Claims

1. A protection circuit is applicable to a switched-capacitor voltage regulator circuit. The switched-capacitor voltage regulator circuit includes a capacitor. The protection circuit includes: A current source having a current input terminal and a current output terminal; A first switch circuit selectively electrically connecting the current source to a top end or a bottom end of the capacitor; A second switching circuit, connected in parallel with the top end and the bottom end of the capacitor; And A control unit. In a first operation stage, the control unit controls the second switch circuit to conduct and controls the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor, so that the top end and the bottom end of the capacitor are electrically connected, and the control unit sets the voltages of the top end and the bottom end of the capacitor to a default high voltage. In a second operation stage, the control unit controls the second switch circuit to cut off, so that the top end and the bottom end of the capacitor are not electrically connected, and controls the first switch circuit to conduct, connecting the current input terminal of the current source to the bottom end of the capacitor. When a voltage difference between the top end and the bottom end of the capacitor is equal to a default initial voltage, the control unit enters a third operation stage; And It is characterized in that, in the third operation stage, the control unit controls the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor, and then controls the first switch circuit according to the voltage of the top end of the capacitor to selectively electrically connect one of the current input terminal and the current output terminal of the current source to the top end of the capacitor.

2. The protection circuit according to claim 1, characterized in that The switched-capacitor voltage regulator circuit receives an input voltage, and the default initial voltage is half of the input voltage.

3. The protection circuit according to claim 2, characterized in that, In the first operation stage, when the input voltage is gradually rising, the control unit determines whether the voltage of the top end of the capacitor is higher than or equal to the default high voltage to decide whether to enter the second operation stage.

4. The protection circuit according to claim 1, characterized in that In the third operation stage, when the control unit determines that the voltage of the top end of the capacitor is higher than a first threshold voltage, the control unit controls the first switch circuit to electrically connect the current input terminal of the current source to the top end of the capacitor.

5. The protection circuit according to claim 4, characterized in that, In the third operation stage, when the control unit determines that the voltage of the top end of the capacitor is lower than a second threshold voltage, the control unit controls the first switch circuit to electrically connect the current output terminal of the current source to the top end of the capacitor.

6. The protection circuit according to claim 5, characterized in that The first threshold voltage is higher than the second threshold voltage.

7. A method for operating a protection circuit, characterized in that, The protection circuit is applicable to a switched-capacitor voltage regulator circuit. The switched-capacitor voltage regulator circuit includes a capacitor. The protection circuit includes a current source, a first switch circuit and a second switch circuit. The operation method includes: Controlling the second switch circuit to conduct, electrically connecting a top end and a bottom end of the capacitor, and controlling the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor, and setting the voltages of the top end and the bottom end of the capacitor to a default high voltage; When the voltages at the top end and the bottom end of the capacitor are equal to the default high voltage, control the second switch circuit to be turned off, so that the top end and the bottom end of the capacitor are not electrically connected, and control the first switch circuit to electrically connect a current inflow end of the current source to the bottom end of the capacitor; and When a voltage difference between the top end and the bottom end of the capacitor is equal to a default initial voltage, control the first switch circuit to disconnect the current source from the top end and the bottom end of the capacitor; and Control the first switch circuit to selectively electrically connect one of the current inflow end and a current outflow end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor.

8. The operating method according to claim 7, characterized in that, The step of controlling the first switch circuit to selectively electrically connect one of the current inflow end and the current outflow end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor further includes: When the voltage at the top end of the capacitor is higher than a first threshold voltage, control the first switch circuit to electrically connect the current inflow end of the current source to the top end of the capacitor.

9. The operating method according to claim 8, characterized in that, The step of controlling the first switch circuit to selectively electrically connect one of the current inflow end and the current outflow end of the current source to the top end of the capacitor according to the voltage at the top end of the capacitor further includes: When the voltage at the top end of the capacitor is lower than a second threshold voltage, control the first switch circuit to electrically connect the current outflow end of the current source to the top end of the capacitor.

10. The operating method according to claim 9, wherein, The first threshold voltage is higher than the second threshold voltage.

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