Control circuit and control method

Abstract

The invention discloses a control circuit and a control method for a switching converter. The control circuit comprises a soft start circuit used for generating soft start voltage; the frequency modulation signal generation circuit is used for generating a frequency modulation signal according to the soft start voltage; and the oscillation circuit is used for providing oscillation frequency to control the switching frequency of the switching converter, and in the soft start stage of the switching converter, the oscillation circuit adjusts the oscillation frequency to be increased along with the rise of the soft start voltage according to the frequency modulation signal and does not exceed the set frequency of the normal working stage of the switching converter. The discharge time of the inductor is prolonged through frequency reduction in the soft start stage, so that the accumulation of inductive current is inhibited, the inductive current overshoot is effectively avoided, and the stability of the switching converter is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of switching converter, and particularly relates to a control circuit and a control method. BACKGROUND

[0002] With the rapid development of portable electronic products, switching converters gradually occupy a larger market share due to their numerous superior performances (for example: high efficiency, low quiescent current, small chip area, etc.).

[0003] In the prior art, in order to avoid the impact of excessive inrush current of the switching converter on the system at power-on, a soft start mechanism is usually used to gradually establish the output voltage. However, due to the limitation of the minimum conduction time of the switching converter, the decrease amplitude of the inductor current is less than the increase amplitude in each switching cycle during the soft start stage with low output voltage, which causes the inductor current to continuously accumulate in multiple switching cycles and further causes the inductor current to overshoot, thereby affecting the system stability. SUMMARY

[0004] In view of the above problems, the purpose of the present application is to provide a control circuit and a control method, which can solve the problem of inductor current overshoot during soft start.

[0005] According to an aspect of the present application, a control circuit for a switching converter is provided, comprising: a soft start circuit for generating a soft start voltage; a frequency modulation signal generation circuit for generating a frequency modulation signal according to the soft start voltage; and an oscillation circuit for providing an oscillation frequency to control the switching frequency of the switching converter, wherein during the soft start stage of the switching converter, the oscillation circuit adjusts the oscillation frequency to increase with the increase of the soft start voltage according to the frequency modulation signal, and does not exceed the set frequency in the normal working stage of the switching converter.

[0006] Optionally, the frequency modulation signal generation circuit is configured to provide a current inversely proportional to the soft start voltage as the frequency modulation signal.

[0007] Optionally, the frequency modulation signal generation circuit comprises: a voltage-to-current conversion unit configured to convert a first reference voltage into a first current and convert the soft start voltage into a second current; a difference current generation unit configured to provide a difference current between the second current and the first current; and an output unit configured to output the frequency modulation signal according to the difference current, wherein the difference current decreases with the increase of the soft start voltage.

[0008] Optionally, the voltage-to-current conversion unit includes: a first transistor, with its control terminal connected to the first reference voltage and its second terminal providing the first current, the first terminal being connected to a first power supply terminal; and a second transistor, with its control terminal connected to the soft-start voltage and its second terminal providing the second current, the first terminal being connected to the first power supply terminal. The voltage-to-current conversion unit further includes: a first resistor connected between the first transistor and the first power supply terminal; and a second resistor connected between the second transistor and the first power supply terminal. The differential current generation unit includes: a third transistor, with its first terminal and control terminal shorted and connected to the first current, and its second terminal connected to a second power supply terminal; and a fourth transistor. The transistor has a first end connected to the second current, a control end connected to the control end of the third transistor, and a second end connected to the second power supply end; and a fifth transistor, whose first end and control end are shorted and connected to the first end of the fourth transistor, and whose second end is connected to the second power supply end. The output unit includes: a sixth transistor, whose control end is connected to the control end of the fifth transistor, and whose second end is connected to the second power supply end; a seventh transistor, whose control end and second end are shorted and connected to the first end of the sixth transistor, and whose first end is connected to the first power supply end; and an eighth transistor, whose control end is connected to the control end of the seventh transistor, whose first end is connected to the first power supply end, and whose second end provides the frequency modulation signal.

[0009] Optionally, the oscillation circuit includes: a charging capacitor; a charging current generating unit for providing a charging current; a shunt unit for providing a shunt current of the charging current according to the frequency modulation signal, wherein the charging capacitor is charged according to the difference between the charging current and the shunt current; and an oscillation comparator for comparing the voltage across the charging capacitor with a second reference voltage to provide the oscillation frequency.

[0010] Optionally, the shunt unit includes: a ninth transistor, with its control terminal and a first terminal shorted and connected to the frequency modulation signal; and a tenth transistor, with its control terminal connected to the control terminal of the ninth transistor, its second terminal connected to the second terminal of the ninth transistor, and its first terminal providing the shunt current.

[0011] Optionally, the oscillation circuit includes: a charging capacitor; a charging current generating unit for providing a charging current for the charging capacitor; a reference voltage generating unit for generating a second reference voltage according to the frequency modulation signal; and an oscillation comparator for comparing the voltage across the charging capacitor with the second reference voltage to provide the oscillation frequency, wherein the second reference voltage decreases to a set voltage as the frequency modulation signal decreases.

[0012] According to another aspect of this application, a control method for a switching converter is provided, comprising: generating a soft-start voltage; generating a frequency modulation signal based on the soft-start voltage; providing an oscillation frequency based on the frequency modulation signal such that the oscillation frequency increases with the increase of the soft-start voltage, and does not exceed a set frequency for the normal operation phase of the switching converter; and controlling the switching frequency of the switching converter based on the oscillation frequency.

[0013] Optionally, the step of generating a frequency modulation signal based on the soft-start voltage includes: converting a first reference voltage to generate a first current; converting the soft-start voltage to generate a second current; and providing the frequency modulation signal based on the difference current between the first current and the second current, wherein the difference current decreases as the soft-start voltage increases.

[0014] Optionally, the step of providing an oscillation frequency according to the frequency modulation signal includes: reducing the charging current of the charging capacitor in the oscillation circuit according to the frequency modulation signal; or increasing the second reference voltage provided to the oscillation comparator in the oscillation circuit according to the frequency modulation signal, wherein the oscillation comparator compares the voltage across the charging capacitor with the second reference voltage to provide the oscillation frequency.

[0015] According to the control circuit and control method provided in this application, during the soft-start process, a frequency modulation signal that changes synchronously with the soft-start voltage is generated, and the oscillation frequency is dynamically adjusted using this frequency modulation signal, so that the oscillation frequency gradually increases as the soft-start voltage increases. In other words, by reducing the frequency during the soft-start stage to prolong the discharge time of the inductor, the accumulation of inductor current is suppressed, effectively avoiding inductor current overshoot and improving the stability of the switching converter. Attached Figure Description

[0016] The above and other objects, features and advantages of this application will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 A schematic structural diagram of a switching converter in the prior art is shown;

[0018] Figure 2 This diagram shows a schematic structural diagram of a switching converter according to an embodiment of this application;

[0019] Figure 3 Show Figure 2 A schematic diagram of the intermediate frequency modulation signal generation circuit;

[0020] Figure 4A Schematic structural diagrams of the oscillation circuits in some embodiments are shown;

[0021] Figure 4B Schematic structural diagrams of the oscillator circuits in some other embodiments are shown;

[0022] Figure 5 A schematic waveform diagram of the control circuit of an embodiment of this application is shown.

[0023] Figure 6 A schematic flowchart of the control method according to an embodiment of this application is shown. Detailed Implementation

[0024] Various embodiments of the present application will now be described in more detail with reference to the accompanying drawings. In the various drawings, the same elements are indicated by the same or similar reference numerals. For clarity, the various parts in the drawings are not drawn to scale.

[0025] Furthermore, certain terms are used in this specification and claims to refer to specific components. Those skilled in the art will understand that manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function.

[0026] It should be understood that, in the following description, "circuit" may include single or combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by the programmable circuit. When an element or circuit is said to be "connected" to another element or "connected" between two nodes, it may be directly coupled or connected to the other element, or there may be intermediate elements; the connection between elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected" to another element, it means that there are no intermediate elements between them.

[0027] Furthermore, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0028] It should also be noted that in the various methods and processes of this application, the order of the steps does not imply the order of execution, nor does it constitute any limitation on the implementation process of the embodiments of this application.

[0029] Figure 1 A schematic structural diagram of a switching converter in the prior art is shown. For example... Figure 1 As shown, the switching converter 1 includes a power circuit 10 and a control circuit 100.

[0030] exist Figure 1 The example shown uses a buck architecture as the power circuit 10. Specifically, the input terminal of the power circuit 10, i.e., the input terminal of the buck architecture, receives the input voltage Vin; the output terminal of the power circuit 10, i.e., the output terminal of the buck architecture, provides the output voltage Vout. (See reference...) Figure 1 The power circuit 10 includes a main power transistor 11, a freewheeling power transistor 12, an inductor 13, a capacitor 14, and a load 15.

[0031] The main power transistor 11 and the freewheeling power transistor 12 are connected sequentially between the input terminal and ground (GND). Therefore, the main power transistor 11 is typically referred to as the upper transistor 11, and the freewheeling power transistor 12 as the lower transistor 12. The main power transistor 11 and the freewheeling power transistor 12 are, for example, N-type MOSFETs, and the node between them is called the switching node SW. An inductor 13 is connected between the switching node SW and the output terminal, a capacitor 14 is connected between the output terminal and ground (GND), and a load 15 is connected in parallel with the capacitor 14. Under the control of the corresponding drive signals HS and LS, the main power transistor 11 and the freewheeling power transistor 12 alternately turn on and off. During the conduction of the main power transistor 11, the freewheeling power transistor 12 is off, and the input voltage Vin charges the inductor 13 and supplies power to the output terminal. During the conduction of the freewheeling power transistor 12, the main power transistor 11 is off, and the inductor 13 supplies power to the output terminal via the freewheeling power transistor 12. During continuous switching cycles, the output of power circuit 10 generates a continuous output, which is filtered by capacitor 14 to obtain a roughly constant output voltage Vout.

[0032] The control circuit 100 provides a first drive signal HS for the main power transistor 11 and a second drive signal LS for the freewheeling power transistor 12. (Reference) Figure 1 The control circuit 100 includes an error amplifier 110, a PWM comparator 120, a logic drive circuit 130, and an oscillation circuit 140.

[0033] Error amplifier 110 is used to amplify the difference between the feedback signal FB of the third reference voltage Vref3 and the output voltage Vout, and provides the error signal ES. For example, in... Figure 1 Specifically, the non-inverting input of the error amplifier 110 is connected to the third reference voltage Vref3, and the inverting input is connected to the feedback signal FB.

[0034] Furthermore, in a switching converter with soft-start functionality, it can be as follows: Figure 1 The diagram shows the soft-start circuit (Figure 1 (Not shown in the diagram) A soft-start voltage SS is provided as the third reference voltage Vref3 during the startup phase of the switching converter, thereby controlling the output voltage Vout to gradually increase through the gradually rising soft-start voltage SS, avoiding excessive inrush current during startup. In some embodiments, the soft-start voltage SS can be directly used as the third reference voltage Vref3, in which case the soft-start phase ends when the soft-start voltage SS rises to a first threshold, which is also the third reference voltage Vref3 during the normal operation phase of the switching converter; in other embodiments, the soft-start voltage SS can be used instead of the third reference voltage Vref3 during the soft-start phase, and the switchback to the third reference voltage Vref3, which is always maintained at the first threshold, can be performed after the soft-start phase ends. This application does not impose further limitations or explanations on this.

[0035] PWM comparator 120 compares the error signal ES with the ramp signal RS and provides a pulse width modulation signal T1 based on the comparison result. Figure 1 In this example, the inverting input of the PWM comparator 120 is connected to the error signal ES, and the non-inverting input is connected to the ramp signal RS. In some embodiments, the ramp signal RS may be provided directly from an external source; in other embodiments, the ramp signal RS may be generated based on the sampling current of the main power transistor 11.

[0036] In the prior art, the oscillation circuit 140 provides a clock signal clk with a fixed frequency. The logic drive circuit 130 provides a first drive signal HS and a second drive signal LS based on the pulse width modulation signal T1 and the fixed-frequency clock signal clk, thereby controlling the conduction frequency and conduction duration of the main power transistor 11 and the freewheeling power transistor 12. The specific signal generation logic should be well known to those skilled in the art. For example, the logic drive circuit 130 may turn on the main power transistor 11 based on the valid edge of the clock signal clk and turn off the main power transistor 11 based on the valid edge of the pulse width modulation signal T1. Further details will not be provided here.

[0037] The switching converter needs to be set with a minimum on-time Tmin to prevent the main power transistor 11 from failing to turn on fully due to an excessively short on-time. However, due to the limitation of Tmin, during the soft-start phase when the output voltage Vout is low, the current drop of inductor 13 in each switching cycle is less than the rise, causing the current of inductor 13 to accumulate continuously over multiple switching cycles, resulting in inductor current overshoot and affecting system stability.

[0038] To address this issue, this application provides a control circuit for a switching converter that avoids inductor current overshoot by reducing the frequency during the soft-start phase.

[0039] Figure 2A schematic structural diagram of a switching converter 200 according to an embodiment of this application is shown; Figure 3 Show Figure 2 A schematic diagram of the intermediate frequency modulation signal generation circuit; Figure 4A Schematic structural diagrams of the oscillation circuits in some embodiments are shown; Figure 4B Schematic structural diagrams of the oscillator circuits in some other embodiments are shown; Figure 5 A schematic waveform diagram of the control circuit according to an embodiment of this application is shown below. Figures 2 to 5 The control circuit provided in the embodiments of this application will be described in detail.

[0040] refer to Figure 2 In the switching converter 2, power circuit 10 is still used as an example. The descriptions of the main power transistor 11, freewheeling power transistor 12, inductor 13, capacitor 14, and load 15 can be found in the above description. Figure 1 The description is as follows. However, it should be noted that the control circuit 200 of this application can be associated with power circuits of any topology to implement different types of switching converters. For example, depending on the type of power circuit, it can be implemented as a buck converter, boost converter, flyback converter, and buck-boost converter, etc. Furthermore, the power circuit can be as follows: Figure 2 The dual-transistor structure (synchronous rectification) shown can also be a single-transistor structure (asynchronous rectification) with a main power transistor and a freewheeling diode. The topology of the power circuit should be well known to those skilled in the art, and will not be described in detail here.

[0041] The control circuit 200 includes an error amplifier 210, a PWM comparator 220, a logic drive circuit 230, an oscillation circuit 240, a soft-start circuit 250, and a frequency modulation signal generation circuit 260.

[0042] The error amplifier 210, PWM comparator 220, and logic drive circuit 230 can be referenced. Figure 1 The error amplifier 110, PWM comparator 120, and logic drive circuit 130 in the figure are used to implement this, or they can be implemented by any related technology, which will not be described in detail here.

[0043] The soft-start circuit 250 is used to generate a soft-start voltage SS. The soft-start circuit 250 can be implemented, for example, through an RC charging and discharging circuit, or through any other related technology. In some embodiments, the soft-start voltage SS may be used instead of the third reference voltage Vref3 during the soft-start phase, and the circuit may switch back to the third reference voltage Vref3, which is always maintained at a first threshold, after the soft-start phase ends. However, it should be understood that this application is not limited thereto. For example, in some other embodiments, the soft-start voltage SS is directly used as the third reference voltage Vref3, in which case the soft-start phase ends when the soft-start voltage SS rises to the first threshold, which is also the third reference voltage Vref3 during the normal operation phase of the switching converter. In the following description, the example of directly using the soft-start voltage SS as the third reference voltage Vref3 will be used.

[0044] The oscillation circuit 240 is used to provide a clock signal clk. The oscillation frequency of the clock signal clk is used to control the switching frequency of the switching converter.

[0045] The frequency modulation signal generation circuit 260 provides a frequency modulation signal CF based on the soft-start voltage SS, so that the oscillation frequency provided by the oscillation circuit 240 increases with the increase of the soft-start voltage during the soft-start phase, but does not exceed the set frequency during normal operation. In other words, according to the control circuit of this application, the oscillation frequency is reduced by the frequency modulation signal CF during the soft-start phase to prolong the discharge time of the inductor, thereby suppressing the accumulation of inductor current, effectively avoiding inductor current overshoot, and improving the stability of the switching converter.

[0046] In some embodiments, the frequency modulation signal generation circuit 260 specifically generates a current that varies inversely with the soft-start voltage SS as the frequency modulation signal CF. Specifically, as shown... Figure 3 As shown, the frequency modulation signal generation circuit 260 specifically includes: a voltage-to-current conversion unit 261, a differential current generation unit 262, and an output unit 263.

[0047] The voltage-to-current conversion unit 261 is used to convert the first reference voltage Vref1 into a first current I1 and the soft-start voltage SS into a second current I2. The first reference voltage Vref1 should be less than or equal to the third reference voltage Vref3. This corresponds to the example where the soft-start voltage SS is directly used as the third reference voltage Vref3; that is, the first reference voltage Vref1 should be less than or equal to the maximum value of the soft-start voltage SS (i.e., the aforementioned first threshold).

[0048] Specifically, the voltage-to-current conversion unit 261 includes a first transistor M1 and a second transistor M2. The control terminal of the first transistor M1 is connected to a first reference voltage Vref1, its second terminal provides a first current I1, and its first terminal is connected to a first power supply terminal VDD. The control terminal of the second transistor M2 is connected to a soft-start voltage SS, its second terminal provides a second current I2, and its first terminal is connected to the first power supply terminal VDD.

[0049] The differential current generating unit 262 is used to provide the differential current Id between the second current I2 and the first current I1. Specifically, the differential current generating unit 262 includes a third transistor M3, a fourth transistor M4, and a fifth transistor M5. The first terminal and the control terminal of the third transistor M3 are shorted and connected to the first current I1, and the second terminal is connected to the second power supply terminal VSS. The first terminal of the fourth transistor M4 is connected to the second current I2, the control terminal is connected to the control terminal of the third transistor M3, and the second terminal is connected to the second power supply terminal VSS. The first terminal and the control terminal of the fifth transistor M5 are shorted and connected to the first terminal of the fourth transistor M4, and the second terminal is connected to the second power supply terminal VSS. Since the fourth transistor M4 and the third transistor M3 form a current mirror structure, the current flowing through the fourth transistor M4 is the first current I1, and the current flowing through the fifth transistor M5 is the differential current Id between the second current I2 and the first current I1.

[0050] Output unit 263 is used to output a frequency modulation signal CF based on the differential current Id. Specifically, output unit 263 includes a sixth transistor M6, a seventh transistor M7, and an eighth transistor M8. The control terminal of the sixth transistor M6 is connected to the control terminal of the fifth transistor M5, and its second terminal is connected to the second power supply terminal VSS. The first terminal of the seventh transistor M7 is connected to the first power supply terminal VDD, and its control terminal and second terminal are shorted and connected to the first terminal of the sixth transistor M6. The first terminal of the eighth transistor M8 is connected to the first power supply terminal VDD, its control terminal is connected to the control terminal of the seventh transistor M7, and its second terminal provides the frequency modulation signal CF.

[0051] The first transistor M1, the second transistor M2, the seventh transistor M7, and the eighth transistor M8 are, for example, NMOS transistors, and the third transistor M3 to the sixth transistor M6 are, for example, PMOS transistors. It should be understood that when a MOS transistor is turned on, current flows from its first terminal to its second terminal. For an NMOS transistor, the first terminal, the second terminal, and the control terminal are the drain, the source, and the gate, respectively; for a PMOS transistor, the first terminal, the second terminal, and the control terminal are the source, the drain, and the gate, respectively.

[0052] As the soft-start voltage SS increases, the second current I2 gradually decreases, while the first current I1 remains unchanged. Therefore, the differential current Id decreases as the soft-start voltage SS increases, which in turn causes the frequency modulation signal CF obtained by replicating the differential current Id to gradually decrease as well.

[0053] Furthermore, in some embodiments, the voltage-to-current conversion unit 261 further includes a first resistor R1 and a second resistor R2. The first resistor R1 is connected between the first terminal of the first transistor M1 and the first power supply terminal VDD, and is used to adjust the magnitude of the first current I1; the second resistor R2 is connected between the first terminal of the second transistor M2 and the first power supply terminal VDD, and is used to adjust the magnitude of the second current I2. The first resistor R1 and the second resistor R2 can be equal, and by setting the resistance ratio of R1 and R2, the magnitude of the frequency modulation signal CF can be further adjusted.

[0054] The oscillation circuit 240 adjusts the oscillation frequency according to the frequency modulation signal CF, which changes inversely to the soft-start voltage SS, thereby dynamically reducing the oscillation frequency during the soft-start phase.

[0055] Figure 4A An oscillator circuit 240a is shown in some embodiments. For example... Figure 4A As shown, the oscillation circuit 240a includes a charging current generating unit 241, a charging capacitor 242, an oscillation comparator 243, a reference voltage generating unit 244, a reset unit 245, and a shunt unit 246.

[0056] The charging current generating unit 241 is used to generate the charging current Ic. The shunt unit 246 is used to provide a shunt current for the charging current Ic according to the frequency modulation signal CF. The shunt charging current (i.e., the difference between the charging current Ic and the shunt current) is used to charge the charging capacitor 242, causing the voltage difference across it to increase.

[0057] Specifically, the shunt unit 246 includes a ninth transistor M9 and a tenth transistor M10. The control terminal and the first terminal of the ninth transistor M9 are shorted and connected to the frequency modulation signal CF. The control terminal of the tenth transistor M10 is connected to the control terminal of the ninth transistor M9, the second terminal is connected to the second terminal of the ninth transistor M9 and connected to the second power supply terminal VSS, and the first terminal provides the shunt current. The ninth transistor M9 and the tenth transistor M10 form a mirror current source structure, making the shunt current proportional to the frequency modulation signal CF. The second power supply terminal VSS can be grounded (GND).

[0058] The reference voltage generation unit 244a generates a second reference voltage Vref2, which serves as the reference level for the oscillation comparator 243. When the voltage across the charging capacitor 242 rises to the second reference voltage Vref2, the oscillation comparator 243 flips, thereby changing the potential of the clock signal clk.

[0059] For example, in Figure 4AIn this circuit, the non-inverting input of the oscillation comparator 243 is connected to the charging capacitor 242, and the inverting input is connected to the reference voltage generation unit 244a to receive the second reference voltage Vref2. When the voltage across the charging capacitor is lower than the second reference voltage Vref2, the oscillation comparator outputs a low-level clock signal clk; when the voltage across the charging capacitor reaches or exceeds the second reference voltage Vref2, the oscillation comparator 243 outputs a high-level clock signal clk. When the clock signal clk transitions to a high level, it triggers the reset unit 245 to discharge the charging capacitor 242, causing its voltage to drop rapidly and starting the next charge / discharge cycle.

[0060] according to Figure 4A The provided oscillation circuit 240a, when the soft-start voltage SS is at its minimum, has a maximum frequency modulation signal CF and a maximum shunt current, thus minimizing the effective charging current supplied to the charging capacitor 242. As the soft-start voltage SS increases, the frequency modulation signal CF decreases, and the shunt current also decreases, leading to an increase in the effective charging current flowing into the charging capacitor 242. This accelerates the charging speed, and the voltage across the charging capacitor reaches the second reference voltage Vref2 more quickly, thereby shortening the oscillation period and increasing the oscillation frequency.

[0061] Figure 4B A schematic diagram of the oscillation circuit 240b in another embodiment is shown. In the oscillation circuit 240b, the operation of the reset unit 245 and the oscillation comparator 243 is similar to... Figure 4A The oscillator circuit shown is the same as 240a, and will not be described again here. (Similar to...) Figure 4A The difference is that, in Figure 4B In this process, the charging current Ic generated by the charging current generating unit 241 is directly used to charge the charging capacitor 242. Meanwhile, the frequency modulation signal CF is provided to the reference voltage generating unit 244b to adjust the second reference voltage Vref2', so that the second reference voltage Vref2' decreases as the frequency modulation signal CF decreases, until it decreases to a preset second threshold.

[0062] As an example, the reference voltage generation unit 244b may include a reference current generation module for generating a reference current and a conversion module for converting the reference current into a reference voltage. The reference current may be compensated by a frequency modulation signal CF, thereby increasing the second reference voltage Vref2' during the soft-start phase. When the soft-start voltage SS is at its minimum, the frequency modulation signal CF is at its maximum, and the second reference voltage Vref2' is at its highest. As the soft-start voltage SS increases, the frequency modulation signal CF decreases, and the second reference voltage Vref2' decreases accordingly. The voltage across the charging capacitor 242 more easily reaches its threshold, thereby accelerating the flip-flop frequency of the comparator 243 and increasing the oscillation frequency.

[0063] Figure 5A schematic diagram of the operating waveforms of the control circuit 200 provided according to an embodiment of this application is shown. The system is powered on at time t1, and the switching converter 2 enters the soft-start phase. The soft-start phase ends at time t2, and the system enters the normal operating phase. During the period from t1 to t2, the soft-start voltage SS gradually rises to a first threshold. Furthermore... Figure 5 In this example, the first reference voltage Vref1 is used as the first threshold. The second current I2 gradually decreases as the soft-start voltage SS rises, reaching the same level as the first current I1 at time t2. Since the first current I1 is controlled by the first reference voltage Vref1 and remains constant between t1 and t2, the differential current Id gradually decreases during this period, causing a gradual decrease in the frequency reduction of the clock signal clk, meaning the oscillation frequency of the clock signal clk gradually increases. After time t2, the soft start is complete, the clock signal clk reaches the set frequency for normal operation, and the system enters steady-state operation.

[0064] According to the control circuit provided in this application, during the soft-start process, a frequency modulation signal that changes synchronously with the soft-start voltage is generated, and the oscillation frequency is dynamically adjusted using this frequency modulation signal, so that the oscillation frequency gradually increases as the soft-start voltage increases. In other words, by reducing the frequency during the soft-start stage, the discharge time of the inductor is extended, thereby suppressing the accumulation of inductor current, effectively avoiding inductor current overshoot, and improving the stability of the switching converter.

[0065] Furthermore, this application also provides a control method for a switching converter, which can be implemented, for example, by the control circuit provided in this application. Figure 6 A schematic flowchart illustrating the control method of an embodiment of this application is shown. Figure 6 As shown, the control method provided in this application includes:

[0066] Step S11: Generate the soft-start voltage.

[0067] The soft-start voltage increases with power-up time. In some embodiments, the soft-start voltage may be used instead of the third reference voltage connected to the error amplifier during the soft-start phase, and the connection between the error amplifier and the third reference voltage may be restored after the soft-start phase ends. However, it should be understood that this application is not limited thereto; for example, in some other embodiments, the soft-start voltage is directly used as the third reference voltage provided to the error amplifier. The soft-start phase ends when the soft-start voltage rises to a first threshold, which is also the third reference voltage during the normal operation phase of the switching converter.

[0068] Step S12: Generate a frequency modulation signal based on the soft-start voltage.

[0069] In some embodiments, the frequency modulation signal may be inversely proportional to the soft-start voltage. Specifically, the frequency modulation signal is manifested as a current value that decreases as the soft-start voltage increases. Step S12 then specifically includes: converting a first reference voltage to generate a first current; converting the soft-start voltage to generate a second current; and providing a frequency modulation signal based on the difference current between the first current and the second current. The difference current decreases as the soft-start voltage increases, and the first reference voltage does not exceed the aforementioned first threshold.

[0070] Step S13: Provide an oscillation frequency based on the frequency modulation signal, so that the oscillation frequency increases with the increase of the soft-start voltage, and does not exceed the set frequency of the normal operation phase of the switching converter.

[0071] In some embodiments, this step may be referred to as... Figure 4A or Figure 4B The provided oscillation circuit implements this. Specifically, it can either decrease the effective charging current of the charging capacitor in the oscillation circuit based on the frequency modulation signal, or increase the second reference voltage provided to the oscillation comparator in the oscillation circuit based on the frequency modulation signal. The oscillation comparator compares the voltage difference across the charging capacitor with the second reference voltage to provide the oscillation frequency.

[0072] Step S14: Provide the switching frequency of the switching converter based on the oscillation frequency.

[0073] According to the control method provided in this application, during the soft-start process, a frequency modulation signal that changes synchronously with the soft-start voltage is generated, and the oscillation frequency is dynamically adjusted using this frequency modulation signal, so that the oscillation frequency gradually increases as the soft-start voltage increases. In other words, by reducing the frequency during the soft-start stage, the discharge time of the inductor is extended, thereby suppressing the accumulation of inductor current, effectively avoiding inductor current overshoot, and improving the stability of the switching converter.

[0074] It should be noted that the control method of this application embodiment is also applicable to other types of oscillator circuits and oscillation frequency generation methods. The goal is simply to achieve the lowest oscillation frequency at the beginning of the soft-start phase and gradually increase it as the soft-start voltage rises. In a preferred embodiment, when the soft-start phase ends, the oscillation frequency reaches the set frequency for the normal operation phase of the switching converter. At this point, the switching converter switches to the normal operation phase.

[0075] As described above, these embodiments of this application do not exhaustively cover all details, nor do they limit this application to specific embodiments. Clearly, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of this application, thereby enabling those skilled in the art to effectively utilize this application and its modifications. The scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A control circuit for a switching converter, wherein, include: A soft-start circuit is used to generate a soft-start voltage; A frequency modulation signal generation circuit is used to generate a frequency modulation signal based on the soft-start voltage; as well as An oscillation circuit is used to provide an oscillation frequency to control the switching frequency of the switching converter. During the soft-start phase of the switching converter, the oscillation circuit adjusts the oscillation frequency according to the frequency modulation signal to increase as the soft-start voltage increases, without exceeding the set frequency of the normal operation phase of the switching converter.

2. The control circuit according to claim 1, wherein, The frequency modulation signal generation circuit is used to provide a current that changes inversely to the soft-start voltage as the frequency modulation signal.

3. The control circuit according to claim 2, wherein, The frequency modulation signal generation circuit includes: A voltage-to-current conversion unit is used to convert a first reference voltage into a first current and to convert the soft-start voltage into a second current. A differential current generating unit is used to provide a differential current between the second current and the first current; and The output unit is used to output the frequency modulation signal according to the differential current. The differential current decreases as the soft-start voltage increases.

4. The control circuit according to claim 3, wherein, The voltage-to-current conversion unit includes: The first transistor has a control terminal connected to the first reference voltage, a second terminal providing the first current, and a first terminal connected to the first power supply terminal. The second transistor has a control terminal connected to the soft-start voltage, a second terminal providing the second current, and a first terminal connected to the first power supply terminal. A first resistor connected between the first transistor and the first power supply terminal; and A second resistor connected between the second transistor and the first power supply terminal. The differential current generating unit includes: The third transistor has its first terminal shorted to the control terminal and connected to the first current, and its second terminal connected to the second power supply terminal. The fourth transistor has a first terminal connected to the second current, a control terminal connected to the control terminal of the third transistor, and a second terminal connected to the second power supply terminal; and The fifth transistor has its first terminal shorted to the control terminal and connected to the first terminal of the fourth transistor, and its second terminal connected to the second power supply terminal. The output unit includes: The sixth transistor has its control terminal connected to the control terminal of the fifth transistor, and its second terminal connected to the second power supply terminal. The seventh transistor has its control terminal shorted to the second terminal and connected to the first terminal of the sixth transistor, the first terminal being connected to the first power supply terminal; and The eighth transistor has a control terminal connected to the control terminal of the seventh transistor, a first terminal connected to the first power supply terminal, and a second terminal providing the frequency modulation signal.

5. The control circuit according to claim 4, wherein, The oscillation circuit includes: Charging capacitor; A charging current generating unit is used to provide charging current; A shunt unit is configured to provide a shunt current for the charging current based on the frequency modulation signal, and the charging capacitor is charged based on the difference between the charging current and the shunt current; and An oscillation comparator is used to compare the voltage across the charging capacitor with a second reference voltage to provide the oscillation frequency.

6. The control circuit according to claim 5, wherein, The splitting unit includes: The ninth transistor, with its control terminal and the first terminal shorted and connected to the frequency modulation signal; and The tenth transistor has a control terminal connected to the control terminal of the ninth transistor, a second terminal connected to the second terminal of the ninth transistor, and a first terminal providing the shunt current.

7. The control circuit according to claim 4, wherein, The oscillation circuit includes: Charging capacitor; A charging current generating unit is used to provide the charging current for the charging capacitor; A reference voltage generation unit is configured to generate a second reference voltage based on the frequency modulation signal; and An oscillation comparator is used to compare the voltage across the charging capacitor with a second reference voltage to provide the oscillation frequency. The second reference voltage decreases to a set voltage as the frequency modulation signal decreases.

8. A control method for a switching converter, wherein, include: Generate soft-start voltage; A frequency modulation signal is generated based on the soft-start voltage; An oscillation frequency is provided according to the frequency modulation signal so that the oscillation frequency increases with the increase of the soft-start voltage, but does not exceed the set frequency of the normal operating phase of the switching converter; and The switching frequency of the switching converter is controlled according to the oscillation frequency.

9. The control method according to claim 8, wherein, The step of generating a frequency modulation signal based on the soft-start voltage includes: Transform the first reference voltage to generate the first current; Convert the soft-start voltage to generate a second current; and The frequency modulation signal is provided based on the difference current between the first current and the second current. The differential current decreases as the soft-start voltage increases.

10. The control method according to claim 9, wherein, The step of providing an oscillation frequency based on the frequency modulation signal includes: The charging current of the charging capacitor in the oscillation circuit is reduced according to the frequency modulation signal; or The second reference voltage provided to the oscillation comparator in the oscillation circuit is increased according to the frequency modulation signal. The oscillation comparator compares the voltage across the charging capacitor with the second reference voltage to provide the oscillation frequency.

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