A load switch soft start circuit based on charge pump

Abstract

This invention provides a load switch soft-start circuit based on a charge pump, including a load switch circuit and an external soft-start control capacitor connected outside the load switch circuit. The load switch circuit utilizes the boost characteristic of the charge pump module to provide a startup voltage for the switching transistor NM1, and uses the gradual voltage rise characteristic of the charge pump to control the gradual rise of the load voltage. This invention utilizes the rise characteristic of the charge pump to achieve the soft-start process, and the charge pump module is originally one of the functional modules of the load switch. The innovative combination design of the charge pump module and the soft-start module significantly reduces circuit overhead while achieving the soft-start function. This circuit avoids most of the soft-start circuitry, retaining only the capacitor used to adjust the soft-start duration, thus optimizing circuit overhead to the maximum extent while ensuring the complete soft-start function.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit technology, and more specifically to a load switch soft-start circuit based on a charge pump. Background Technology

[0002] During startup, power management chips may experience inrush current that could burn them out. A soft-start circuit can reduce this inrush current and allow the output voltage to rise slowly. Therefore, power management chips are designed with this scenario in mind, incorporating a soft-start module.

[0003] Power management chip load switches also require soft-start circuits to suppress inrush current, but a standalone soft-start circuit can result in significant circuit overhead.

[0004] Therefore, a soft-start circuit with optimized circuit overhead is needed. Summary of the Invention

[0005] This invention addresses the issue of optimizing circuit overhead by providing a charge pump-based soft-start circuit for a load switch. It utilizes the rise characteristics of the charge pump to achieve the soft-start process, and the charge pump module is inherently a functional module of the load switch. By innovatively combining the charge pump module and the soft-start module, circuit overhead is significantly reduced while still achieving the soft-start function. This circuit avoids most of the soft-start circuitry, retaining only the capacitor used to adjust the soft-start duration, thus maximizing circuit overhead optimization while ensuring the completeness of the soft-start function.

[0006] This invention provides a load switch soft-start circuit based on a charge pump, including 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-up voltage for the switch transistor NM1, and uses the voltage gradually rising characteristic of the charge pump to realize the soft start of the switch transistor NM1. At the same time, the boost time of the charge pump module is adjusted by controlling the soft start time.

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

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

[0009] The charge pump module includes a boost circuit and an enable circuit. The output of the boost circuit is connected to the drain of the MOS transistor 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 the soft-start signal and high-voltage signal of the load switching circuit. The voltage signal VG is output to the gate of the switching transistor NM1.

[0010] V TH V is the threshold voltage of the switching transistor NM1. When the gate-source voltage of the switching transistor NM1 is greater than the threshold voltage V... TH At this time, the switching transistor NM1 is turned on;

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

[0012] During the start-up phase of the load switching circuit, VG <VIN+V TH When switching transistor NM1 is turned off, the output voltage VOUT is no greater than VG-V. TH ;

[0013] The boost circuit gradually increases the voltage signal VG. Limited by the switching transistor NM1, the output voltage VOUT rises at a rate not exceeding VG-V. TH The rise rate of the voltage signal VG can control the rise rate of the output VOUT for soft start.

[0014] After the switching transistor NM1 completes startup, VG > VIN + V TH The output voltage VOUT is equal to VIN.

[0015] The load switch soft-start circuit based on a charge pump described in this invention, in a preferred embodiment, includes an enable circuit comprising a resistor R1 and a PMOS transistor PM1 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 terminal of the boost circuit.

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

[0017] The gate of transistor NM2 receives the enable signal EN, and its source is grounded. The source of transistor PM1 is connected to resistor R1 and the input voltage VIN, and its drain is connected to the positive terminal of transistor D1. Its gate is connected between the other end of resistor R1 and the drain of transistor NM2. The other ends of capacitors C1 and C3 are both connected to the CLK clock signal. The other ends of capacitors C2 and C4 are both grounded. The gate of transistor NM3 receives the EN_N signal, and its source is grounded.

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

[0019] In a preferred embodiment of the load switch soft-start circuit based on a charge pump described in this invention, when the EN signal is low and the EN_N signal is high, transistor NM2 is turned off, transistor NM3 is turned on, and transistor PM1 is turned off, and the charge pump module outputs a low level.

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

[0021] In the present invention, a load switch soft-start circuit based on a charge pump is preferably provided in which the CLK clock signal is a periodic signal.

[0022] When the CLK clock signal is low, transistors D1, D2, D3, and D4 are turned on, and the input voltage VIN charges capacitors C1, C2, C3, and C4 until the voltage of capacitors C1, C2, C3, and C4 is VIN.

[0023] When the CLK clock signal changes from low to high, the voltage across capacitors C1 and C3 becomes VIN+VDD. Transistors D1 and D3 are inverted and cut off, while transistors D2 and D4 are forward-biased and conduct. Capacitors C1 and C3 transfer charge to capacitors C2 and C4 until the voltages across capacitors C1, C2, C3, and C4 are equal.

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

[0025] In the charge pump-based load switch soft-start circuit of 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 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, the longer it takes for the voltage signal VG to rise to the target value. Users can select the size of the external soft-start control capacitor Css_ex according to the actual use scenario to set the soft-start time.

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

[0028] In a preferred embodiment of the load switch soft-start circuit based on a charge pump described in this invention, the input of the pre-regulator circuit is VIN, the output is the operating voltage VDD, and the pre-regulator circuit operates when the enable signal EN is high.

[0029] In a preferred embodiment of the load switch soft-start circuit based on a charge pump described in this invention, the clock signal module is a clock generation circuit that outputs a clock signal CLK. The power supply for the clock signal module is VDD, and it operates when the enable signal EN is high.

[0030] The principle of this invention is as follows: the boost process of the Charge Pump and the turn-on characteristics of the switching transistor are used to control the start-up rise process of the output. The time of the Charge Pump boost process is controlled 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] This invention provides a soft-start circuit for load switches. This circuit utilizes the rise characteristics of a charge pump to achieve the soft-start process, and the charge pump module is originally one of the functional modules of the load switch. By innovatively combining the charge pump module and the soft-start module, circuit overhead is significantly reduced while still achieving the soft-start function. This circuit avoids most of the soft-start circuitry, retaining only the capacitor used to adjust the soft-start duration, thus optimizing circuit overhead to the maximum extent while ensuring the complete soft-start function. Attached Figure Description

[0033] Figure 1 This is a circuit diagram of a load switch soft-start circuit based on a charge pump;

[0034] Figure 2 This is an inverted circuit diagram of a load switch with soft-start function based on a charge pump;

[0035] Figure 3 This is a pre-regulatory circuit diagram for a load switch with soft-start function based on a charge pump;

[0036] Figure 4 This is a circuit diagram for generating a clock for a load switch with soft-start function based on a charge pump.

[0037] Figure 5 This is a soft-start circuit diagram of a load switch with soft-start function based on a charge pump. Detailed Implementation

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0039] Example 1

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

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

[0042] U1 is an inverter circuit. Its input is the chip enable signal EN, and its output is its inverted signal EN_N. When EN changes from low to high, the system starts up and the circuit is powered on.

[0043] REG is a pre-regulator circuit with input VIN and output VDD. VDD is the internal module's operating power supply. The module's enable signal is EN; it operates when EN is high.

[0044] The ICO is a clock generation circuit, outputting CLK. It provides the periodic signal for the Charge Pump boost. The module's power supply is VDD, and its enable signal is EN. The ICO module operates when EN is high.

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

[0046] Resistor R1, and MOSFETs PM1, NM2, and NM3 constitute the enable circuit for the Charge Pump. When EN is low and EN_N is high, NM2 is off, NM3 is on, and PM1 is off, resulting in a low-level output from the Charge Pump. When EN is high and EN_N is low, NM2 is on, NM3 is off, and PM1 is on, allowing the Charge Pump to operate normally.

[0047] Diodes D1, D2, D3, and D4, and capacitors C1, C2, C3, and C4 constitute the boost circuit of the Charge Pump. When CLK is low, D1, D2, D3, and D4 conduct, and VIN charges capacitors C1, C2, C3, and C4 until the voltage across C1, C2, C3, and C4 equals VIN (ignoring the forward conduction voltage of the diodes). When CLK changes from low to high, the voltage across C1 and C3 becomes VIN + VDD. D1 and D3 are reverse-biased and cut off, while D2 and D4 conduct. C1 and C3 transfer charge to C2 and C4 until the voltage across C1, C2, C3, and C4 are equal.

[0048] The charge pump requires 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 time. This circuit utilizes the gradually rising voltage characteristic of the charge pump to achieve the soft-start function.

[0049] NM1 is the switching transistor for the load switch. Due to the switching characteristics, it is known that when the gate-source voltage of the switching transistor is greater than the threshold voltage V... TH The switching transistor is turned on; when the gate-source voltage of the switching transistor is less than the threshold voltage V... TH The switching transistor 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 limitations of the switching transistor, the rise rate of VOUT cannot exceed VG-V. TH Therefore, the rate of VG's rise can control the rate of output rise. After startup, VG > VIN + V TH The output voltage VOUT is equal to VIN.

[0050] Css_in is an internal soft-start control capacitor used to control the soft-start time. The larger the value of Css_in, the longer it takes for VG to rise to the target value. Css_in is integrated inside the chip and is fixed in the early stages of the design.

[0051] Css_ex is an external soft-start control capacitor used to control the soft-start time. A larger Css_ex value results in a longer time for VG to rise to the target value. Users can select an appropriate Css_ex, i.e., an appropriate soft-start time, based on their actual usage scenario, allowing for greater application flexibility.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A load switch soft-start circuit based on a charge pump, characterized in that: The device includes a charge pump module connected in the load switching circuit and an external soft-start control capacitor connected outside the load switching circuit. The load switching circuit uses the boost characteristic of the charge pump module to provide a start-up voltage for the switching transistor NM1, and uses the voltage gradually rising characteristic of the charge pump to realize the soft start of the switching transistor 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 switching circuit includes a pre-regulatory circuit for controlling startup, a clock signal module, a charge pump module, a switching transistor NM1 connected to the output terminal of the charge pump module, and an internal soft-start control capacitor Css_in. The gate of the switching transistor NM1 is connected to the output terminal of the charge pump module, the drain is connected to the input voltage VIN, and the source is connected to the output terminal VOUT. The output terminal SS of the load switching circuit is connected to both the internal soft-start control capacitor Css_in and the output terminal of the charge pump module. The external soft-start control capacitor is connected to the output terminal SS. The charge pump module includes a boost circuit and an enable circuit. The output terminal of the boost circuit is connected to the drain of the MOS transistor 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 the soft-start signal and high-voltage signal of the load switching circuit. The voltage signal VG is output to the gate of the switching transistor NM1. V TH The threshold voltage of the switching transistor NM1 is defined as follows: when the gate-source voltage of the switching transistor NM1 is greater than the threshold voltage V... TH When this occurs, the switching transistor NM1 is turned on; When the enable signal EN changes from low level to high level, the load switching circuit starts to power on; During the startup phase of the load switch circuit, VG <VTN+V TH When the switching transistor NM1 is turned off, the output voltage VOUT is not greater than VG-V. TH ; The boost circuit gradually increases the voltage signal VG. Limited by the switching transistor NM1, the output voltage VOUT rises at a rate not exceeding VG-V... TH The rise rate of the voltage signal VG can control the rise rate of the output VOUT to perform soft start. After the switching transistor NM1 completes startup, VG>VIN+V TH The output voltage VOUT is equal to VIN.

2. The 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 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 terminal of the boost circuit. The boost circuit includes diodes D1, D2, D3, and D4 whose positive terminals are connected to the drain of transistor PM1 in sequence; capacitor C1 connected between the negative terminal of transistor D1 and the positive terminal of transistor D2; capacitor C2 connected between the negative terminal of transistor D2 and the positive terminal of transistor D3; capacitor C3 connected between the negative terminal of transistor D3 and the positive terminal of transistor D4; and capacitor C4 connected between the negative terminal of transistor D4 and the drain of transistor NM3. The gate of transistor NM2 receives the enable signal EN, and its source is grounded. The source of transistor PM1 is connected to resistor R1 and the input voltage VIN, and its drain is connected to the positive terminal of transistor D1. Its gate is connected between the other end of resistor R1 and the drain of transistor NM2. The other ends of capacitors C1 and C3 are both connected to the CLK clock signal. The other ends of capacitors C2 and C4 are both grounded. The gate of transistor NM3 receives the EN_N signal, and its source is grounded. The other end of the internal soft-start control capacitor Css_in is grounded.

3. The load switch soft-start circuit based on a charge pump according to claim 2, characterized in that: When the EN signal is low and the EN_N signal is high, transistor NM2 is turned off, transistor NM3 is turned on, and transistor PM1 is turned off, and the charge pump module outputs a low level. When the EN signal is high and the EN_N signal is low, transistor NM2 is turned on, transistor NM3 is turned off, and transistor PM1 is turned on, and the charge pump module works 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 low, transistors D1, D2, D3, and D4 are turned on, and the input voltage VIN charges capacitors C1, C2, C3, and C4 until the voltage of capacitors C1, C2, C3, and C4 is VIN. When the CLK clock signal changes from low to high, the voltage across capacitors C1 and C3 becomes VIN+VDD. Transistors D1 and D3 are inverted and cut off, while transistors D2 and D4 are forward-biased and conduct. Capacitors C1 and C3 transfer charge to capacitors C2 and C4 until the voltages across capacitors C1, C2, C3, and C4 are equal. The charge pump module requires at least two clock cycles to raise the voltage signal VG to the target value, and can be used as a soft-start signal.

5. A load switch soft-start circuit based on a 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, the longer it takes for the voltage signal VG to rise to the target value, and the longer the soft-start time. 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, the longer it takes for the voltage signal VG to rise to the target value. Users can select the size of the external soft-start control capacitor Css_ex according to the actual use scenario to set the soft-start time.

6. The load switch soft-start circuit based on a charge pump according to claim 1, characterized in that: The charge pump module includes an inverting circuit U1, which inverts the enable signal EN into the 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-regulatory circuit is VIN, and the output is the operating voltage VDD. The pre-regulatory circuit operates when the enable signal EN is high.

8. A load switch soft-start circuit based on a charge pump according to claim 6, characterized in that: The clock signal module is a clock generation circuit that outputs a clock signal CLK. The power supply for the clock signal module is VDD, and it operates when the enable signal EN is high.

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