Load switch soft start circuit based on charge pump

Abstract

The invention provides a load switch soft start circuit based on a charge pump. The load switch soft start circuit comprises a load switch circuit and an external soft start control capacitor connected outside the load switch circuit. The load switch circuit provides a starting voltage for a switch tube NM1 by using the boost characteristic of a charge pump module, and controls the load voltage to gradually rise by using the voltage gradual rise characteristic of a charge pump. The soft start process is realized by using the rising characteristic of the charge pump, and the charge pump module is originally one of the function modules of the load switch. The charge pump module and the soft start module are innovatively combined and designed, so that the circuit overhead is greatly reduced on the premise of realizing the soft start function. According to the circuit, most of soft start circuits are avoided, only the capacitor used for adjusting the soft start time is reserved, and the circuit overhead is optimized to the maximum under the condition that the soft start function is complete.

Description

Technical Field

[0001] The invention relates to the technical field of integrated circuits, and in particular to a load switch soft start circuit based on a charge pump. Background Art

[0002] During the startup process of the power management chip, there may be a surge current that may cause the chip to burn out. The soft start circuit can reduce the surge current when the power is started, so that the output voltage rises slowly. Therefore, when the power management chip is designed, this situation will be taken into consideration and a soft start module will be designed specifically.

[0003] The load switch of the power management chip also requires a soft-start circuit to suppress the inrush current, but a separate soft-start circuit will cause a large circuit overhead.

[0004] Therefore, a soft start circuit that can optimize circuit overhead is needed. Summary of the invention

[0005] The present invention aims to optimize the problem of circuit overhead, and provides a load switch soft start circuit based on a charge pump, which uses the rising characteristics of the charge pump to realize the soft start process, and the charge pump module is originally one of the functional modules of the load switch. The charge pump module and the soft start module are innovatively combined and designed, and the circuit overhead is greatly reduced under the premise of realizing the soft start function. The circuit avoids most of the soft start circuits and only retains the capacitor used to adjust the soft start time. Under the condition of ensuring that the soft start function is complete, the circuit overhead is optimized to the maximum.

[0006] The present invention provides a load switch soft start circuit based on a charge pump, comprising a charge pump module connected in the load switch circuit and an external soft start control capacitor connected outside the load switch circuit, the load switch circuit uses the boost characteristic of the charge pump module to provide a start voltage for a switch tube NM1, and uses the voltage gradually rising characteristic of the charge pump to realize the soft start of the switch tube NM1, and at the same time adjusts the boost time of the charge pump module by controlling the soft start time;

[0007] including a load switch circuit and an external soft start control capacitor connected outside the load switch circuit;

[0008] The load switch circuit includes a pre-stabilizing circuit for controlling startup, a clock signal module and a charge pump module connected to the pre-stabilizing circuit in sequence, and a switch tube NM1 and an internal soft-start control capacitor Css_in respectively connected to the output end of the charge pump module. The gate of the switch tube NM1 is connected to the output end of the charge pump module, the drain is connected to the input voltage VIN, and the source is connected to the output end VOUT. The output end SS of the load switch circuit is connected to both the internal soft-start control capacitor Css_in and the output end of the charge pump module, and the external soft-start control capacitor is connected to the output end SS.

[0009] The charge pump module includes a boost circuit and an enable circuit. The output end of the boost circuit is connected to the drain of the MOS tube NM3 of the enable circuit and then connected in parallel with the internal soft start control capacitor Css_in and outputs a voltage signal VG. The voltage signal VG is a soft start signal and a high voltage signal of the load switch circuit. The voltage signal VG is output to the gate of the switch tube NM1.

[0010] V TH is the threshold voltage of the switch tube NM1. When the gate-source voltage of the switch tube NM1 is greater than the threshold voltage V TH When , the switch tube NM1 is turned on;

[0011] When the enable signal EN changes from low level to high level, the load switch circuit starts to power on;

[0012] During the startup phase of the load switch circuit, VG <VIN+V TH , the switch tube NM1 is turned off, and the output voltage VOUT is not greater than VG-V TH ;

[0013] The boost circuit gradually increases the voltage signal VG. Limited by the switch tube NM1, the output voltage VOUT rises at a rate not exceeding VG-V TH , the rising speed of the voltage signal VG can control the rising speed of the output VOUT to perform soft start;

[0014] When the switch tube NM1 is started, VG>VIN+V TH , the output voltage VOUT is equal to VIN.

[0015] The load switch soft start circuit based on charge pump described in the present invention, as a preferred embodiment, the enabling circuit includes a resistor R1 and a PMOS transistor PM1 respectively connected to the input voltage VIN, an NMOS transistor NM2 whose drain is connected to the other end of the resistor R1, and an NMOS transistor NM3 whose drain is connected to the output end of the boost circuit;

[0016] The boost circuit includes diodes D1, D2, D3, and D4 whose positive electrodes are connected to the drain of tube PM1 in sequence, a capacitor C1 connected between the negative electrode of tube D1 and the positive electrode of tube D2, a capacitor C2 connected between the negative electrode of tube D2 and the positive electrode of tube D3, a capacitor C3 connected between the negative electrode of tube D3 and the positive electrode of tube D4, and a capacitor C4 connected between the negative electrode of tube D4 and the drain of tube NM3;

[0017] The gate of tube NM2 inputs the enable signal EN and the source is grounded; the source of tube PM1 is connected to the resistor R1 and the input voltage VIN, the drain is connected to the positive electrode of tube D1, and the gate is connected between the other end of resistor R1 and the drain of tube NM2; the other end of capacitor C1 is connected to the other end of capacitor C3 and both input the CLK clock signal, the other end of capacitor C2 and the other end of capacitor C4 are grounded, the gate of tube NM3 inputs the EN_N signal and the source is grounded;

[0018] The other end of the internal soft start control capacitor Css_in is grounded.

[0019] The load switch soft start circuit based on charge pump described in the present invention is, as a preferred embodiment, when the EN signal is at a low level and the EN_N signal is at a high level, the tube NM2 is turned off, the tube NM3 is turned on, the tube PM1 is turned off, and the charge pump module outputs a low level;

[0020] When the EN signal is at a high level and the EN_N signal is at a low level, the tube NM2 is turned on, the tube NM3 is turned off, and the tube PM1 is turned on, and the charge pump module works normally.

[0021] In the load switch soft start circuit based on a charge pump described in the present invention, as a preferred embodiment, the CLK clock signal is a periodic signal;

[0022] When the CLK clock signal is at a low level, tubes D1, D2, D3, and D4 are turned on, and the input voltage VIN charges the capacitors C1, C2, C3, and C4 until the voltage of the capacitors C1, C2, C3, and C4 reaches VIN;

[0023] When the CLK clock signal changes from low level to high level, the voltage across capacitors C1 and C3 becomes VIN+VDD, tubes D1 and D3 are reverse-phase cutoff, tubes D2 and D4 are forward-phased, and capacitors C1 and C3 transfer charges to capacitors C2 and C4 until the voltages of capacitors C1, C2, C3, and C4 are equal;

[0024] The charge pump module needs at least two clock cycles to increase the voltage signal VG to the target value, which can be used as a soft start signal.

[0025] In the load switch soft start circuit based on a charge pump described in the present invention, as a preferred embodiment, the internal soft start control capacitor Css_in can also control the soft start time; the larger the capacitance value of the internal soft start control capacitor Css_in, the longer the time it takes for the voltage signal VG to rise to the target value;

[0026] The other end of the external soft-start control capacitor Css_ex is also grounded. The larger the capacitance value of the external soft-start control capacitor Css_in is, the longer it takes for the voltage signal VG to rise to the target value. The user can select the size of the external soft-start control capacitor Css_ex to set the soft-start time according to the actual usage scenario.

[0027] In the load switch soft start circuit based on a charge pump described in the present invention, as a preferred embodiment, the charge pump module includes an inverting circuit U1, and the inverting circuit U1 inverts the enable signal EN into a signal EN_N.

[0028] The load switch soft start circuit based on charge pump described in the present invention is, as a preferred embodiment, the input of the pre-stabilizing circuit is VIN, the output is the working voltage VDD, and the pre-stabilizing circuit works when the enable signal EN of the pre-stabilizing circuit is high level.

[0029] The load switch soft start circuit based on charge pump described in the present invention is, as a preferred embodiment, the clock signal module is a clock generating circuit, the output is the clock signal CLK, the power supply of the clock signal module is VDD, and it works when the enable signal EN is at a high level.

[0030] The principle of the present invention is to control the output startup rising process by utilizing the boosting process of the Charge Pump and the opening characteristics of the switch tube, and to control the boosting time of the Charge Pump by the size of the output capacitor of the Charge Pump, thereby indirectly controlling the soft start time.

[0031] The present invention has the following advantages:

[0032] The present invention provides a soft start circuit for a load switch, wherein the circuit utilizes the rising characteristic of a charge pump to realize the soft start process, and the charge pump module is originally one of the functional modules of the load switch. The charge pump module and the soft start module are innovatively combined and designed, and the circuit overhead is greatly reduced under the premise of realizing the soft start function. The circuit avoids most of the soft start circuits and only retains the capacitor for adjusting the soft start time. Under the condition of ensuring that the soft start function is complete, the circuit overhead is optimized to the maximum. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a load switch soft start circuit diagram based on a charge pump;

[0034] Figure 2 The invention is a circuit inversion circuit diagram of a load switch with a soft start function based on a charge pump;

[0035] Figure 3 A pre-regulator circuit diagram of a load switch with a soft start function based on a charge pump;

[0036] Figure 4 A clock generation circuit diagram for a load switch with a soft start function based on a charge pump;

[0037] Figure 5 The present invention is a soft start circuit diagram of a load switch with a soft start function based on a charge pump. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0039] Example 1

[0040] like Figure 1 As shown, a load switch soft-start circuit based on a charge pump includes an enabling circuit for controlling the startup of each circuit module; a pre-regulator module (REG) for providing internal working power for the chip; an ICO module for generating a clock signal; a Charge Pump module for generating a high-voltage signal for providing the voltage required for turning on the switch tube; and a soft-start control capacitor for controlling the soft-start time.

[0041] like Figures 2 to 5 As shown in the figure, the soft start circuit applied to Load Switch is as follows:

[0042] U1 is an inverting circuit, the input is the chip enable signal EN, and the output is its inverted signal EN_N. When EN changes from low level to high level, the system starts to start and the circuit starts to power on.

[0043] REG is a pre-regulator circuit, the input is the input power supply VIN, and the output is VDD. VDD is the internal module working power supply. The module enable signal is EN, and it works when EN is high.

[0044] ICO is a clock generation circuit, and its output is CLK. It provides a periodic signal for the Charge Pump boost. The power supply of this module is VDD, and the enable signal is EN. When EN is high, the ICO module works.

[0045] R1, PM1, NM2, NM3, D1, D2, D3, D4, C1, C2, C3, and C4 constitute a Charge Pump circuit.

[0046] Resistor R1, MOS tubes PM1, NM2, and NM3 form the enable circuit of Charge Pump. When EN is low and EN_N is high, NM2 is turned off, NM3 is turned on, PM1 is turned off, and Charge Pump output is low. When EN is high and EN_N is low, NM2 is turned on, NM3 is turned off, PM1 is turned on, and Charge Pump works normally.

[0047] Diodes D1, D2, D3, D4 and capacitors C1, C2, C3, C4 form the boost circuit of Charge Pump. When CLK is low, D1, D2, D3, D4 are turned on, and VIN charges capacitors C1, C2, C3, C4 until the voltage of C1, C2, C3, C4 is VIN (ignore the forward voltage of the diode). When CLK changes from low to high, the voltage across C1 and C3 becomes VIN+VDD, D1 and D3 are reversed and cut off, D2 and D4 are forward-conducted, and C1 and C3 transfer the charge to C2 and C4 until the voltages of C1, C2, C3, and C4 are equal.

[0048] The Charge Pump needs multiple clock cycles to raise the output signal to the target value, so the output VG of the Charge Pump is a voltage signal that gradually increases from low to high. The soft start circuit also requires the output signal to gradually rise to the target position within a certain period of time. This circuit uses the gradual voltage rise characteristic of the Charge Pump to achieve the soft start function.

[0049] NM1 is the switch tube of the load switch. As the conduction characteristics of the switch tube show, when the gate-source voltage of the switch tube is greater than the threshold voltage V TH , the switch is turned on; when the gate-source voltage of the switch is less than the threshold voltage V TH , the switch tube is turned off. During the startup phase, VG <VIN+V TH , the output voltage VOUT is not greater than VG-V TH Due to the limitation of the switch tube, the speed of VOUT rising cannot exceed VG-V TH Therefore, the speed of VG's rise can control the speed of output rise. After the startup is completed, VG>VIN+V TH , the output voltage VOUT is equal to VIN.

[0050] Css_in is the soft start control capacitor inside the chip, which is used to control the soft start time. The larger the capacitance value of Css_in, the longer it takes for VG to rise to the target value. Css_in is integrated inside the chip and will be fixed at the beginning of the design.

[0051] Css_ex is the soft start control capacitor outside the chip, which is used to control the soft start time. The larger the capacitance value of Css_ex, the longer it takes for VG to rise to the target value. Users can choose the appropriate Css_ex according to the actual usage scenario, that is, choose the appropriate soft start time, which makes the application more flexible.

[0052] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A load switch soft start circuit based on a charge pump, characterized in that: The load switch circuit comprises a charge pump module connected in the load switch circuit and an external soft start control capacitor connected outside the load switch circuit. The load switch circuit uses the boost characteristic of the charge pump module to provide a start voltage for the switch tube NM1, and uses the voltage gradually rising characteristic of the charge pump to realize the soft start of the switch tube NM1. At the same time, the soft start time is controlled by the external soft start control capacitor to adjust the boost time of the charge pump module. The load switch circuit includes a pre-stabilizing circuit for controlling startup, a clock signal module connected to the pre-stabilizing circuit in sequence, the charge pump module, and a switch tube NM1 respectively connected to the output end of the charge pump module, and an internal soft start control capacitor Css_in, wherein the gate of the switch tube NM1 is connected to the output end of the charge pump module, the drain is connected to the input voltage VIN, and the source is connected to the output end VOUT, the output end SS of the load switch circuit is connected to both the internal soft start control capacitor Css_in and the output end of the charge pump module, and the external soft start control capacitor is connected to the output end SS; The charge pump module includes a boost circuit and an enable circuit. The output end of the boost circuit is connected to the drain of the MOS tube NM3 of the enable circuit and then connected in parallel with the internal soft start control capacitor Css_in to output a voltage signal VG. The voltage signal VG is a soft start signal and a high voltage signal of the load switch circuit. The voltage signal VG is output to the gate of the switch tube NM1. V TH is the threshold voltage of the switch tube NM1. When the gate-source voltage of the switch tube NM1 is greater than the threshold voltage V TH When , the switch tube NM1 is turned on; When the enable signal EN changes from a low level to a high level, the load switch circuit starts to power on; During the startup phase of the load switch circuit, VG <VTN+V TH , the switch tube NM1 is turned off, and the output voltage VOUT is not greater than VG-V TH ; The boost circuit gradually increases the voltage signal VG. Limited by the switch tube NM1, the output voltage VOUT rises at a speed not exceeding VG-V TH The rising speed of the voltage signal VG can control the rising speed of the output VOUT to perform soft start; When the switch tube NM1 is started, VG>VIN+V TH , the output voltage VOUT is equal to VIN.

2. A load switch soft start circuit based on a charge pump according to claim 1, characterized in that: The enabling circuit includes a resistor R1 and a PMOS transistor PM1 respectively connected to the input voltage VIN, an NMOS transistor NM2 whose drain is connected to the other end of the resistor R1, and an NMOS transistor NM3 whose drain is connected to the output end of the boost circuit; The boost circuit includes diodes D1, D2, D3, and D4 whose positive electrodes are sequentially connected to the drain electrode of tube PM1, a capacitor C1 connected between the negative electrode of tube D1 and the positive electrode of tube D2, a capacitor C2 connected between the negative electrode of tube D2 and the positive electrode of tube D3, a capacitor C3 connected between the negative electrode of tube D3 and the positive electrode of tube D4, and a capacitor C4 connected between the negative electrode of tube D4 and the drain electrode of tube NM3; The gate of tube NM2 inputs the enable signal EN and the source is grounded; the source of tube PM1 is connected to the resistor R1 and the input voltage VIN, the drain is connected to the positive electrode of tube D1, and the gate is connected between the other end of resistor R1 and the drain of tube NM2; the other end of capacitor C1 is connected to the other end of capacitor C3 and both input the CLK clock signal, the other end of capacitor C2 and the other end of capacitor C4 are grounded, the gate of tube NM3 inputs the EN_N signal and the source is grounded; The other end of the internal soft start control capacitor Css_in is grounded.

3. A load switch soft start circuit based on a charge pump according to claim 2, characterized in that: When the EN signal is at a low level and the EN_N signal is at a high level, the tube NM2 is turned off, the tube NM3 is turned on, and the tube PM1 is turned off, and the charge pump module outputs a low level; When the EN signal is at a high level and the EN_N signal is at a low level, the tube NM2 is turned on, the tube NM3 is turned off, and the tube PM1 is turned on, and the charge pump module operates normally.

4. The load switch soft start circuit based on a charge pump according to claim 2, characterized in that: The CLK clock signal is a periodic signal; When the CLK clock signal is at a low level, tubes D1, D2, D3, and D4 are turned on, and the input voltage VIN charges the capacitors C1, C2, C3, and C4 until the voltage of the capacitors C1, C2, C3, and C4 reaches VIN; When the CLK clock signal changes from low level to high level, the voltage across capacitors C1 and C3 becomes VIN+VDD, tubes D1 and D3 are reverse-phase cutoff, tubes D2 and D4 are forward-phased, and capacitors C1 and C3 transfer charges to capacitors C2 and C4 until the voltages of capacitors C1, C2, C3, and C4 are equal; The charge pump module requires at least two clock cycles to increase the voltage signal VG to a target value, which can be used as a soft start signal.

5. The load switch soft start circuit based on charge pump according to claim 1, characterized in that: The internal soft start control capacitor Css_in can also control the soft start time; the larger the capacitance value of the internal soft start control capacitor Css_in is, the longer the time it takes for the voltage signal VG to rise to the target value, and the longer the soft start time is; The other end of the external soft-start control capacitor Css_ex is also grounded. The larger the capacitance value of the external soft-start control capacitor Css_in is, the longer it takes for the voltage signal VG to rise to the target value. The user can select the size of the external soft-start control capacitor Css_ex to set the soft-start time according to the actual usage scenario.

6. The load switch soft start circuit based on charge pump according to claim 1, characterized in that: The charge pump module includes an inverting circuit U1 , which inverts an enable signal EN into a signal EN_N.

7. A load switch soft start circuit based on a charge pump according to claim 6, characterized in that: The input of the pre-voltage regulator circuit is VIN, and the output is the working voltage VDD. The pre-voltage regulator circuit works when the enable signal EN of the pre-voltage regulator circuit is at a high level.

8. The load switch soft start circuit based on charge pump according to claim 6, characterized in that: The clock signal module is a clock generating circuit, and its output is a clock signal CLK. The power supply of the clock signal module is VDD, and the clock signal module works when the enable signal EN is at a high level.

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