A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit

Abstract

This invention provides a fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit. The differentiating circuit, composed of an operational amplifier, samples the slope of the output voltage to determine its slope. Negative feedback is used to control the internal soft-start voltage, achieving different slopes. This ensures that the output voltage slope remains the same regardless of the external voltage division resistor ratios. After soft-start, the circuit can shut off the bias current of the start-up circuit via a soft-start termination signal, achieving zero static power consumption.

Description

Technical Field

[0001] This invention belongs to the field of switching power supplies and their power-on startup technology, specifically relating to a fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit. Background Technology

[0002] Power management chips, a type of analog chip, are the heart of electronic devices' power supply, responsible for functions such as power conversion, distribution, and detection. Their performance directly impacts the performance and reliability of electronic products, and they are widely used in various electronic products, representing one of the largest segments of the analog chip market. Switching converter circuits are a major component of power management chips, and soft-start circuits are essential for the power-on startup process of these circuits. Without a soft-start circuit, surges will occur during power-on, causing voltage overshoot and circuit damage.

[0003] Currently, most existing DC-DC chip soft-start circuits are fixed-time soft-start circuits, which typically charge a fixed capacitor with a fixed current and determine the output using a comparator. They offer advantages such as controllable timing and simple implementation. However, fixed-slope output voltage soft-start is a new application requirement that has emerged in recent years, and related circuits or technical descriptions are scarce in current domestic and international papers and patents. Because fixed-slope output voltage soft-start circuits can ensure a stable, high-precision, and fast power supply during device startup, they are suitable for various power conversion applications and therefore have greater advantages and development prospects.

[0004] The challenge of a soft-start circuit with a fixed output voltage slope lies in the fact that different chip users have different requirements for the output voltage, so the ratio of the external voltage divider resistors will also be different.

[0005] (1-1)

[0006] Where N is the resistance ratio of the two external voltage divider resistors, Vref is the internal reference voltage, and VOUT is the output voltage. If the internal soft-start circuit uses a traditional constant slope soft-start voltage (fixed-time soft-start circuit), the slope of the output voltage will change due to the different voltage divider resistors. Within the output voltage range, the slope difference can reach more than 5 times. In some circuits sensitive to supply voltage stress, this may cause functional damage or even device damage.

[0007] Patent application number 202110789542.1 proposes a soft-start control circuit for achieving constant output voltage slope startup, as shown in the attached specification. Figure 1 As shown. Its principle is achieved by internally adding a resistor with a fixed voltage ratio (…). Figure 1During soft-start, the operational amplifiers in the main loop of the switching converter (R3, R4) are disconnected (see attached manual). Figure 2 The hysteresis comparator in the middle is used for selection) to the control signal of the PWM comparator ( Figure 1 (Vea in the middle), and the fixed slope voltage signal generated internally ( Figure 2 The 142 circuit is directly connected to the PWM comparator. Since the voltage division ratio and the voltage division resistor are fixed, the output voltage rise slope is a fixed value. Furthermore, the feedback voltage FB1 is compared with the reference voltage Vref. When the FB voltage approaches Vref, the fixed slope voltage signal is disconnected, and the op-amp output is reconnected to the PWM comparator to ensure that the slope of the circuit's output voltage is not affected by the external voltage division resistor, thus achieving a fixed-slope soft-start of the output voltage.

[0008] However, it also has the following problems:

[0009] ① An additional set of fixed-ratio voltage divider resistors is used internally. In low quiescent current applications, this resistance needs to reach the MΩ level, which greatly increases the chip area.

[0010] ② During the startup and normal operation phases, the input signal in the PWM modulation comparator in the main loop needs to be switched. Since it cannot be guaranteed that the op-amp's output voltage will match the soft-start voltage during switching, the output voltage will be uneven, resulting in a poorer soft-start effect. (This is illustrated in the simulation diagram of this patent, as shown in the attached specification.) Figure 3 (As shown) Summary of the Invention

[0011] To address the shortcomings and deficiencies of existing technologies, this invention proposes a fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit. This circuit samples the slope of the output voltage through a differentiating circuit composed of operational amplifiers. This method solves the problem of determining the output voltage slope under different voltage divider resistor ratios in the external circuit. Furthermore, negative feedback is used to control the internal soft-start voltage to achieve different slopes, thus ensuring that the output voltage slope remains the same regardless of the external voltage divider resistor ratios. After soft-start is complete, the circuit can shut off the bias current of the start-up circuit via a soft-start end signal, achieving zero static power consumption.

[0012] The specific technical solution adopted by this invention to solve its technical problem is as follows:

[0013] A fixed-slope soft-start circuit using an operational amplifier differentiating circuit samples the slope of the output voltage through the differentiating circuit composed of an operational amplifier to determine the slope of the output voltage; and uses negative feedback to control the internal soft-start voltage to achieve different slopes, thereby ensuring that the output voltage slope is the same when the external voltage divider resistor ratio is different.

[0014] Furthermore, the slope of the internal soft-start voltage signal is adaptively changed according to the different external voltage divider resistors, so that the rising slope of the output voltage always remains the same; that is, Kout=N*Kss, where, for different N, a corresponding Kss is adaptively generated internally by the system to make Kout a fixed value.

[0015] Furthermore, the voltage output V out Connect one end of capacitor C1, and connect the other end of capacitor C1 to the inverting input terminal of amplifier EA1 and one end of resistor R1; connect voltage V to the non-inverting input terminal of amplifier EA1. B1 The corresponding voltage V at the output terminal d Connect the other end of resistor R1 to the inverting input of amplifier EA2;

[0016] Amplifier EA2's non-inverting input is connected to voltage VB2, and its output is connected to the gate of switching transistor MP1; the source of switching transistor MP1 is connected to voltage input V. in The drain is connected to the drain of the switching transistor MN1 and serves as the soft-start voltage V. soft The acquisition terminal; the gate of the switching transistor MN1 is connected to the soft start signal SS_START, the source is grounded, and a capacitor C2 is connected in parallel between the source and drain.

[0017] Furthermore, capacitor C1, resistor R1, and amplifier EA1 constitute a differentiating circuit used to sample the slope of the output voltage; its formula is:

[0018]

[0019] Wherein, voltage V B1 R1 and C1 are known design values; different output voltage slopes dV out / dt corresponds to different Vd values.

[0020] Furthermore, amplifier EA2 is connected to voltage V B2 The slope setting circuit, due to the clamping effect of amplifier EA2, causes V to... B2 =V d The slope of the output voltage can be set by adjusting the value of VB2.

[0021] Furthermore, a soft-start voltage control circuit is constructed using switching transistors MP1 and MN1, and capacitor C2; when the soft-start start signal SS_START is low, the circuit enters the soft-start state; the voltage V obtained after sampling the slope... d Voltage value and V B2The comparison yields the output voltage of amplifier EA2. The output voltage of amplifier EA2 controls MP1 to charge capacitor C2, thus obtaining the soft-start voltage V. soft .

[0022] Furthermore, due to the soft-start voltage V soft The slope of the circuit determines the slope of the output voltage. The entire circuit forms a closed-loop negative feedback loop to ensure that the output voltage can start according to the set slope and to ensure that the slope of the output voltage is the set value.

[0023] Furthermore, it also includes a comparator circuit for converting the soft-start voltage V... soft With reference voltage V REF Compare; when V soft Voltage greater than V REF When the signal SS_OVER is displayed, it indicates that the soft start has ended. The comparator circuit outputs the signal SS_OVER to turn off the bias current inside amplifiers EA1 and EA2.

[0024] Furthermore, the amplifier EA2 is a single-stage operational amplifier with a bandwidth greater than the loop bandwidth of the BUCK circuit.

[0025] Compared with the prior art, the main features and advantages of the present invention and its preferred embodiments include at least the following:

[0026] ① No additional internal fixed voltage divider resistors are required, reducing the chip area.

[0027] ② It does not require switching of the feedback signals within the system loop during the startup and stable operation phases, thus avoiding startup irregularities caused by switching.

[0028] ③ After the soft start is completed, the two operational amplifiers can be turned off to achieve almost zero quiescent current. Attached Figure Description

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0030] Figure 1 Existing technology principle block diagram;

[0031] Figure 2 Existing soft-start control circuit diagram;

[0032] Figure 3 Simulation results of existing technology;

[0033] Figure 4 This is a diagram showing the location of the soft-start circuit with a fixed output voltage slope in an embodiment of the present invention.

[0034] Figure 5 This is a circuit schematic diagram of an embodiment of the present invention;

[0035] Figure 6 This is a schematic diagram of the operational amplifier circuit used in an embodiment of the present invention;

[0036] Figure 7 The circuit simulation results of the embodiment of the present invention are shown in the figure: (a) internal soft start voltage Vsoft (b) output voltage Vout. Detailed Implementation

[0037] To make the features and advantages of this patent more apparent and understandable, specific embodiments are provided below for detailed explanation:

[0038] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0039] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0040] To achieve a soft-start circuit with a fixed output voltage slope, it's necessary to ensure that the output voltage maintains the same rising slope regardless of different output voltages (due to varying external voltage divider resistors). However, in traditional soft-start circuits, because the internal soft-start voltage signal slope remains constant, the output voltage slope changes proportionally with the voltage divider resistor ratio, i.e., Kout = N * Kss, where Kout is the rising slope of the output voltage Vout, N is the ratio of the external voltage divider resistors, and Kss is the rising slope of the internal soft-start voltage.

[0041] Therefore, in order to achieve a fixed slope start-up, in addition to the methods used in the above-mentioned existing technology patents, such as adding an internal fixed ratio voltage divider circuit, designing the internal soft start electrical signal to a fixed slope, and switching the signal by comparing the feedback voltage with the reference voltage, other technical paths also need to be considered.

[0042] In the solution provided by this embodiment of the invention: the slope of the internal soft-start voltage signal adaptively changes with the different external voltage divider resistors, so that the rising slope of the output voltage always remains the same. That is, in Kout=N*Kss, for different N, a corresponding Kss is adaptively generated internally by the system to make Kout a fixed value.

[0043] The fixed-slope soft-start circuit designed specifically for the output voltage in this embodiment of the invention refers to the circuit located at... Figure 4 Module 1 in the circuit adds output voltage sampling compared to traditional soft-start circuits. The specific circuit of module 1 is as follows: Figure 5 As shown, the design of its main circuit section is as follows:

[0044] The voltage output Vout is connected to one end of capacitor C1, and the other end of capacitor C1 is connected to the inverting input terminal of amplifier EA1 and one end of resistor R1; the non-inverting input terminal of amplifier EA1 is connected to voltage VB1, and the output terminal corresponds to voltage Vd, and is connected to the other end of resistor R1 and the inverting input terminal of amplifier EA2.

[0045] The non-inverting input of amplifier EA2 is connected to voltage VB2, and the output is connected to the gate of switching transistor MP1. The source of switching transistor MP1 is connected to voltage input Vin, and the drain is connected to the drain of switching transistor MN1, which also serves as the acquisition terminal for soft-start voltage Vsoft. The gate of switching transistor MN1 is connected to soft-start signal SS_START, the source is grounded, and a capacitor C2 is connected in parallel between the source and drain.

[0046] Finally, a comparator circuit is included to determine whether the soft start has ended.

[0047] The entire circuit can be divided into four parts. The first part is module 2, which consists of C1, R1, EA1, and voltage VB1. R1 is an adjustable resistor; changing its resistance changes the slope of the output voltage. R1, C1, and EA1 form a differentiating circuit, which samples the slope of the output voltage. The formula is...

[0048] (1-2)

[0049] Because the voltage V B1 R1 and C1 are known design values, so different output voltage slopes dVout / dt can yield different Vd values.

[0050] The second part, module 3, is a slope setting circuit composed of EA2 and voltage VB2. Due to the clamping effect of operational amplifier EA2, V... B2 =V d As can be seen from Equation 1-2, V can be set... B2 The slope of the output voltage is set by the value.

[0051] The third part, module 4, is a soft-start voltage control circuit composed of MP1, MN1, and C2. When the soft-start signal SS_START is low, the circuit enters the soft-start state. The voltage value Vd obtained after sampling the slope is compared with VB2 to obtain the output voltage of EA2. The output voltage of EA2 controls MP1 to charge C2, thus obtaining the soft-start voltage Vsoft. Since the slope of the soft-start voltage Vsoft determines the slope of the output voltage, the three parts together form a closed-loop negative feedback loop. The closed-loop negative feedback ensures that the output voltage can start according to the set slope. And because the slope of the output voltage is directly sampled, regardless of the change in the ratio of the external voltage divider resistors, it can ensure that the slope of the output voltage is the set value.

[0052] Part 4, Module 5, consists of MP2-4, MN2, 3, and INV1. MP2, 3, 4, MN2, and 3 form a comparator that compares the soft-start voltage with a reference voltage. When Vsoft is greater than VREF, it indicates the soft-start is complete, and the SS_OVER signal outputs a high level to shut off the bias current inside EA1 and EA2, achieving zero power consumption in the soft-start circuit.

[0053] The circuit schematics for EA1 and EA2 are as follows: Figure 6 As shown. Since EA2 in the fixed-slope soft-start circuit is an operational amplifier in the loop, it introduces a pole into the main loop when the circuit is working. To ensure loop stability, the bandwidth of EA2 needs to be greater than the loop bandwidth of the BUCK circuit; therefore, only a single-stage operational amplifier can be used in EA2.

[0054] The final circuit implementation effect of this invention is as follows: Figure 7 As shown, when the external output voltage changes (the external voltage divider resistor changes), the slope Vsoft of the soft-start voltage changes, while the slope of the output voltage rise remains unchanged, thus achieving a fixed slope soft start.

[0055] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

[0056] This patent is not limited to the above-described preferred embodiment. Anyone can derive other forms of fixed-slope soft-start circuits using operational amplifier differentiating circuits based on the teachings of this patent. All equivalent variations and modifications made within the scope of this patent application shall fall within the scope of this patent.

Claims

1. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit, characterized in that: The slope of the output voltage is sampled by a differentiating circuit composed of operational amplifiers to determine the slope of the output voltage; negative feedback is used to control the internal soft-start voltage to achieve different slopes, thereby ensuring that the output voltage slope is the same when the external voltage divider resistor ratio is different. Voltage output V out Connect one end of capacitor C1, and connect the other end of capacitor C1 to the inverting input of amplifier EA1 and one end of resistor R1; connect voltage V to the non-inverting input of amplifier EA1. B1 The corresponding voltage V at the output terminal d Connect the other end of resistor R1 to the inverting input of amplifier EA2; Amplifier EA2's non-inverting input is connected to voltage VB2, and its output is connected to the gate of switching transistor MP1; the source of switching transistor MP1 is connected to voltage input V. in The drain is connected to the drain of the switching transistor MN1 and serves as the soft-start voltage V. soft The acquisition terminal; the gate of the switching transistor MN1 is connected to the soft start signal SS_START, the source is grounded, and a capacitor C2 is connected in parallel between the source and drain; Capacitor C1, resistor R1, and amplifier EA1 constitute a differentiating circuit used to sample the slope of the output voltage; its formula is: Wherein, voltage V B1 R1 and C1 are known design values; different output voltage slopes dV out / dt corresponds to different Vd values.

2. The fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 1, characterized in that: The slope of the internal soft-start voltage signal is adaptively changed according to the different external voltage divider resistors, so that the rising slope of the output voltage always remains the same; that is, Kout=N*Kss, where, for different N, a corresponding Kss is adaptively generated internally to make Kout a fixed value.

3. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 1, characterized in that: Amplifier EA2 passes through voltage V B2 The slope setting circuit, due to the clamping effect of amplifier EA2, causes V to... B2 =V d By setting V B2 The value is used to set the slope of the output voltage.

4. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 3, characterized in that: The soft-start voltage control circuit consists of switching transistors MP1 and MN1, and capacitor C2. When the soft-start start signal SS_START is low, the circuit enters the soft-start state. The voltage V obtained after sampling the slope... d Voltage value and V B2 The comparison yields the output voltage of amplifier EA2. The output voltage of amplifier EA2 controls MP1 to charge capacitor C2, thus obtaining the soft-start voltage V. soft .

5. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 4, characterized in that: Due to the soft-start voltage V soft The slope of the circuit determines the slope of the output voltage. The entire circuit forms a closed-loop negative feedback loop to ensure that the output voltage can start according to the set slope and to ensure that the slope of the output voltage is the set value.

6. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 4, characterized in that: It also includes a comparator circuit for converting the soft-start voltage V soft With reference voltage V REF Compare; when V soft Voltage greater than V REF When the signal SS_OVER is displayed, it indicates that the soft start has ended. The comparator circuit outputs the signal SS_OVER to turn off the bias current inside amplifiers EA1 and EA2.

7. A fixed-slope soft-start circuit utilizing an operational amplifier differentiating circuit according to claim 4, characterized in that: The amplifier EA2 is a single-stage operational amplifier with a bandwidth greater than the loop bandwidth of the BUCK circuit.

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