Self-adaptive conduction time generation circuit capable of being synchronized in wide frequency range

Abstract

The invention discloses a self-adaptive conduction time generation circuit capable of being synchronized in a wide frequency range, which generates sink current of an oblique wave generation circuit by utilizing a multiplier in combination with reference frequency, current in direct proportion to the reference frequency and a signal of a sampling circuit, and adjusts conduction time of an MOS (Metal Oxide Semiconductor) tube by utilizing a comparator, a latch and a loop of the oblique wave generation circuit. According to the invention, the conduction time is tuned by introducing an external reference frequency variable, so that the switching frequency can be synchronized by the external frequency, and the switching frequency can be accurately kept unchanged under the condition that the load is stable, and is not influenced by the nonlinearity and matching precision of the circuit; moreover, the ramp current generating the conduction time can be inversely proportional to the frequency and the phase difference to improve the tuning gain of the conduction time, the frequency synchronization range is also improved, and the input and output voltage range of the whole architecture application is widened.

Description

Technical Field

[0001] The invention relates to the technical field of integrated circuit design, and in particular to an adaptive on-time generating circuit capable of synchronization within a wide frequency range. Background Art

[0002] The adaptive on-time circuit is a commonly used structure in power control systems. For example, in a DC-DC inductor-capacitor step-down power supply system, the adaptive on-time circuit is used to generate a fixed on-time that is inversely proportional to the input voltage and proportional to the output voltage, thereby controlling the on-time of the upper power tube. Since in the continuous current mode of the inductor-capacitor step-down system, the switching period is proportional to the on-time of the upper power tube and the input voltage, and is also inversely proportional to the output voltage, when the adaptive on-time circuit is used, the switching period is also fixed within a certain load range, and the entire system is usually called a pseudo-constant frequency control system.

[0003] At present, the BUCK circuit with adaptive on-time function is generally composed of input and output sampling circuit, ramp wave generating circuit and comparison circuit. When the BUCK circuit works in continuous mode, the output voltage and input voltage can be obtained; the switching period of the system, which is the inverse of the system switching frequency, can be obtained. This system has the advantages of fast load transient response in frequency modulation mode, and the system frequency can remain basically unchanged when the input and output are stable. However, the circuit has the following defects in generating on-time: 1) Unstable switching frequency: When the input and output voltages vary widely, especially under extreme conditions such as when the input voltage is the highest and the output voltage is the lowest or when the input voltage is the lowest and the output voltage is the highest, the on-time cannot change nonlinearly, causing the switching frequency to be unable to remain constant over the entire voltage range; 2) It is difficult to make the frequencies of different chips consistent: Non-ideal factors in circuit design include the offset voltage of the operational amplifier, the matching of resistors and MOS devices, etc. These will cause the switching frequency of different chips to deviate even under the same input and output conditions, that is, it is impossible to ensure that the frequency between chips is completely consistent; 3) The switching frequency range is small and the range of selectable devices is small: Once the internal correlation coefficients of the chip are designed, such as the ratio of R2 and R1, the ratio of R3 and R4, and the value of Gm1, the switching frequency of the chip is designed to be within a very small frequency range, and the internal switching frequency cannot be modified at will according to user needs, which further limits the selection range of user peripheral devices. Summary of the invention

[0004] In view of the above three problems, the purpose of the present invention is to propose an adaptive on-time generating circuit that can be synchronized within a wide frequency range. By introducing an external reference frequency variable to tune the on-time, the system switching frequency can be synchronized with the external frequency, and the switching frequency can be accurately maintained unchanged under stable load conditions, without being affected by the nonlinearity and matching accuracy of the circuit, which is convenient for device selection; moreover, the ramp current that generates the on-time can be inversely proportional to the frequency and phase difference to improve the tuning gain of the on-time, and also improve the range of frequency synchronization, broaden the input and output voltage range of the entire architecture application, reduce the range requirement for the loop control voltage, and greatly reduce the problem of continuous frequency changes and small range due to non-ideal factors of the circuit.

[0005] This is achieved through the following technical solutions: A synchronizable adaptive on-time generating circuit within a wide frequency range, used for frequency synchronization between a power supply system and an external system, comprises an external current introducing module, a multiplier, a ramp wave generating circuit, an input sampling circuit, an output sampling circuit, a voltage-to-current circuit 1, an external introducing circuit, a comparator and an SR latch; the external current introducing module is used to receive the switching frequency of the power supply system and the reference frequency of the external system and generate a current I_PHASE, and transmit the current I_PHASE to the IN3 input terminal of the multiplier; the input sampling circuit is used to receive an input voltage VIN and generate a VINO signal, and convert the VINO signal into a current I_VIN via the voltage-to-current circuit 1 and transmit it to the IN1 input terminal of the multiplier; the external introducing circuit adopts a first DC current source to transmit a current I_OSC proportional to the reference frequency to the IN2 input terminal of the multiplier; the output terminal of the multiplier outputs The output end of the multiplier is connected to the ramp wave generating circuit; the ramp wave generating circuit uses the MOS tube to generate a ramp current for controlling the conduction time based on IOUT; the output sampling circuit is connected to the negative input end of the comparator; the output end of the comparator is connected to the ramp wave generating circuit through the SR latch to form a loop, and the SR latch is used to output the conduction time of the MOS tube.

[0006] By adding an external current introduction module, while generating the on-time, it is also possible to introduce external reference frequency or phase difference information to realize the synchronizable function of the switching frequency, which not only solves the shortcoming that users cannot customize the switching frequency in the traditional adaptive on-time module, but also can accurately maintain the switching frequency unchanged under the condition of stable load, and is not affected by the nonlinearity of the circuit and the matching accuracy; moreover, the introduction of the current I_OSC proportional to the reference frequency can greatly increase the synchronizable frequency range, so that the on-time can be adjusted within a wide frequency range; in addition, the ramp wave generating circuit is used for tuning to effectively control the on-time.

[0007] Preferably, the external current introduction module includes a phase frequency detector, a charge pump, a loop filter circuit and a voltage-to-current circuit 2; wherein the input end of the phase frequency detector receives the switching frequency of the power supply system and the reference frequency of the external system, and the output end drives the charge pump to generate a control voltage VCTRL; the loop filter circuit is used to perform loop filtering on the control voltage VCTRL; the voltage-to-current circuit 2 converts the control voltage VCTRL after loop filtering into the current I_PHASE. The phase frequency detector can effectively obtain the phase difference and frequency difference, and then can generate a control voltage together with the charge pump to adjust the frequency and phase of the two systems to be consistent.

[0008] Preferably, the loop filter circuit includes a resistor R6, a capacitor C2 and a capacitor C3, the first end of the resistor R6 is connected in parallel between the charge pump and the voltage-to-current circuit 2, the second end of the resistor R6 is grounded through the capacitor C2, and the capacitor C3 is connected in parallel between the capacitor C2 and the ground and between the charge pump and the voltage-to-current circuit 2. The loop filter circuit can effectively filter out noise and smooth the signal, so that the signal introduced by the external current introduction module is more stable.

[0009] Preferably, the ramp wave generating circuit includes a second DC current source, a MOS tube and a capacitor C1, and the capacitor C1 is grounded; the second DC current source receives AVDD power supply and is connected to the output end of the multiplier to generate a current injection I_SLOPE; the current injection I_SLOPE flows through the capacitor C1 to generate a ramp voltage signal V_SLOPE, and the positive input end of the comparator receives the ramp voltage signal V_SLOPE; the drain of the MOS tube is connected between the second DC current source and the capacitor C1, the source of the MOS tube is connected between the capacitor C1 and the ground, and the gate of the MOS tube is connected to the output end of the SR latch. The ramp wave generating circuit uses a MOS tube to adjust the ramp voltage signal, thereby improving the tuning gain of the conduction time, effectively improving the range of frequency synchronization, and widening the range of the input voltage and output voltage of the overall circuit.

[0010] Preferably, both the input sampling circuit and the output sampling circuit adopt a resistor voltage division structure; the input sampling circuit includes an input voltage VIN, a resistor R1 and a resistor R2 connected in sequence, the resistor R2 is grounded, and the voltage-to-current circuit 1 is connected between the resistor R1 and the resistor R2; the output sampling circuit includes an output voltage VOUT, a resistor R3 and a resistor R4 connected in sequence, the resistor R4 is grounded, and the negative input end of the comparator is connected between the resistor R3 and the resistor R4. The use of a resistor voltage division structure can simplify the design and is also easy to adjust the voltage division ratio.

[0011] Preferably, the voltage-to-current circuit 1 is a resistor-type conversion circuit or an operational amplifier-type conversion circuit. The resistor-type conversion circuit has low cost, and the operational amplifier-type conversion circuit has high precision and is easy to control.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The technical solution of the present invention introduces an external reference frequency variable to tune the on-time, so that the system switching frequency can be synchronized with the external frequency, and can accurately maintain the switching frequency unchanged when the load is stable, without being affected by the nonlinearity and matching accuracy of the circuit, which is convenient for device selection; moreover, the ramp current generated for the on-time can be inversely proportional to the frequency and phase difference to improve the tuning gain of the on-time, and also improve the range of frequency synchronization, broaden the input and output voltage range of the entire architecture application, reduce the range requirement for the loop control voltage, and greatly reduce the problem of continuous frequency changes and small range due to non-ideal factors of the circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of a structure of an adaptive on-time generating circuit that can be synchronized within a wide frequency range; Figure 2 A waveform diagram of frequency synchronization in an adaptive on-time generating circuit that can be synchronized within a wide frequency range; Figure 3 A waveform diagram showing synchronization of a switching frequency with corresponding three voltage waveforms. DETAILED DESCRIPTION

[0014] The technical solutions in the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0015] like Figure 1 As shown, it is a structural schematic diagram of an adaptive on-time generating circuit that can be synchronized within a wide frequency range, which is used for frequency synchronization between a power supply system and an external system, including an external current introduction module, a multiplier, a ramp wave generating circuit, an input sampling circuit, an output sampling circuit, a voltage-to-current circuit 1, an external introduction circuit, a comparator and an SR latch. The parameters of the external current introduction module and the external introduction circuit are introduced through the multiplier to increase the frequency synchronization function and widen the frequency range.

[0016] In this embodiment, the external current introduction module is used to receive the switching frequency of the power system and the reference frequency of the external system and generate the current I_PHASE, and transmit the current I_PHASE to the IN3 input terminal of the multiplier. Specifically, the external current introduction module includes a phase frequency detector, a charge pump, a loop filter circuit and a voltage-to-current circuit 2. The input terminal CLK_REF of the phase frequency detector receives the switching frequency F of the power system. SW The input terminal CLK_DIV of the frequency detector receives the reference frequency F of the external system. OSC, the frequency difference or phase difference of the two frequencies is obtained. Based on the frequency difference or phase difference, the charge pump can be driven to work at the output end, and a control voltage VCTRL can be generated. The types of voltage-to-current circuit 1 and voltage-to-current circuit 2 can both adopt a resistor-type conversion circuit or an operational amplifier-type conversion circuit. For these two conversion circuits, the resistor-type conversion circuit has low cost and is widely used, while the operational amplifier-type conversion circuit has high precision and is easy to control. Users can freely choose from the two schemes. The specific structures of the resistor-type conversion circuit and the operational amplifier-type conversion circuit are not described here. The corresponding schemes are currently very mature and can be selected from the existing schemes.

[0017] The loop filter circuit is used to perform loop filtering on the control voltage VCTRL, effectively filter out noise and smooth the signal, so that the control voltage signal introduced by the external current introduction module is more stable and gentle. Specifically, the structure of the loop filter circuit can be: resistor R6, capacitor C2 and capacitor C3, the first end of the resistor R6 is connected in parallel between the charge pump and the voltage-to-current circuit 2, and the second end of the resistor R6 is connected to the ground AGND through the capacitor C2 to form an RC filter; the capacitor C3 is connected in parallel between the capacitor C2 and the ground and between the charge pump and the voltage-to-current circuit 2 to perform high-frequency filtering. The voltage-to-current circuit 2 converts the control voltage VCTRL that has passed the loop filtering into the current I_PHASE, which is introduced into the IN3 input terminal of the multiplier.

[0018] At the same time, the external introduction circuit uses a grounded first DC current source to transmit a current I_OSC proportional to the reference frequency to the IN2 input terminal of the multiplier.

[0019] The input sampling circuit is used to receive the input voltage VIN and generate the VINO signal, convert the VINO signal into the current I_VIN through the voltage-to-current circuit 1 and transmit it to the IN1 input of the multiplier. The input sampling circuit adopts a resistor voltage-dividing structure, which can simplify the design and is easy to adjust the voltage-dividing ratio. In the input sampling circuit, resistor R1 is connected to the power supply VIN, resistor R2 is grounded, and the voltage-to-current circuit 1 is connected between resistor R1 and resistor R2. The input voltage VIN generates the VINO signal through the input sampling circuit, and the VINO signal generates the current I_VIN proportional to the input voltage signal VIN through the voltage-to-current module 1, and the current I_VIN flows into the IN1 port of the multiplier.

[0020] Therefore, the multiplier can output the signal obtained from the three input terminals at the output terminal. , the output of the multiplier is connected to the ramp generating circuit, which in turn generates a sink current to control the on-time.

[0021] In this embodiment, the ramp wave generating circuit uses a MOS tube to generate a ramp current for controlling the conduction time based on IOUT. The ramp wave generating circuit includes a second DC current source, a MOS tube and a capacitor C1, and the capacitor C1 is grounded; the second DC current source receives AVDD power supply and is connected to the output end of the multiplier to generate a current I_SLOPE; the current I_SLOPE flows through the capacitor C1 to generate a ramp voltage signal V_SLOPE, and the positive input end of the comparator receives the ramp voltage signal V_SLOPE; the drain of the MOS tube is connected between the second DC current source and the capacitor C1, the source of the MOS tube is connected between the capacitor C1 and the ground, and the gate of the MOS tube is connected to the output end of the SR latch. The ramp wave generating circuit uses a MOS tube to adjust the ramp voltage signal, thereby improving the tuning gain of the conduction time, effectively improving the range of frequency synchronization, and widening the range of the input voltage and output voltage of the overall circuit.

[0022] The three signals I_PHASE, I_VIN and I_OSC generate a current I_SLOPE after passing through the multiplier. The I_SLOPE current flows through the capacitor C1 to generate a ramp voltage signal V_SLOPE. The drain of the MOS tube MN0 is connected to the upper plate of C1, the source and the capacitor C1 are shorted to the ground, and the gate is connected to the output VDRN of the subsequent SR latch to form a closed loop for periodic reset of the entire module. In this application, the current I_PHASE proportional to the frequency or phase difference is deliberately connected to the IN3 terminal of the multiplier, that is, the output current I_SLOPE of the multiplier is inversely proportional to I_PHASE in order to further increase the tuning gain of the equivalent voltage-controlled oscillator, thereby ensuring that the switching frequency can always be locked with the external frequency.

[0023] It should be noted that the sink current actually refers to the current that charges the capacitor C1, which can also be called the ramp current here. This is because when the current passes through the capacitor C1, it accumulates charge on the capacitor, thereby generating a voltage that changes linearly with time across the capacitor, that is, the ramp voltage V_SLOPE. When the current I_SLOPE flows through the capacitor C1, it will cause the voltage on the capacitor to gradually rise, forming a ramp-shaped waveform, that is, the current is used to generate a ramp voltage signal.

[0024] The positive end of the comparator is connected to the ramp voltage signal V_SLOPE voltage, and the negative end of the comparator is connected to the output sampling end VOUT0. The output sampling circuit also adopts a resistor voltage divider structure, in which resistor R3 is connected to the output voltage VOUT, resistor R4 is grounded, and the negative input end of the comparator is connected between resistor R3 and resistor R4 to obtain the voltage VOUTO. The output end of the comparator is connected to the reset end R of the SR latch, and the set end S of the SR latch is connected to the short pulse signal VCOMP used to turn on the upper power tube in the power system. The pulse width of the output signal VDR of the SR latch is the conduction time of the upper power tube in the entire power system.

[0025] The entire module of the present application is integrated into the power supply system and can be equivalent to a phase-locked loop system. Through the feedback principle, the switching frequency Fsw of the power supply system can be made to be in the same frequency and phase as the external frequency Fosc. If the system switching frequency Fsw is higher than the external frequency Fosc, the loop control voltage VCTRL becomes higher, and then I_PHASE becomes higher. Since I_SLPOE is inversely proportional to I_PHASE, the on-time becomes longer, and then the system switching frequency Fsw is reduced, until Fsw and Fosc frequency and phase are the same, the system is stable. On the contrary, if the system switching frequency Fsw is lower than the external frequency Fosc, the loop control voltage VCTRL becomes lower, and then I_PHASE becomes smaller. Since I_SLPOE is inversely proportional to I_PHASE, the on-time becomes smaller, and then the system switching frequency Fsw increases, until Fsw and Fosc frequency and phase are the same, the system is stable.

[0026] like Figure 2 As shown, it is a waveform diagram of frequency synchronization in an adaptive on-time generating circuit that can be synchronized within a wide frequency range. As long as the external frequency Fosc remains unchanged, the switching frequency Fsw of the power supply can also be maintained constant, and the control voltage VCTRL, current I_PHASE and current I_SLOPE can also tend to a stable state.

[0027] Similarly, if Figure 3 The figure shows a waveform diagram of the synchronization of the switching frequency and the corresponding three voltage waveforms. t represents the time. SW On the basis of stability, the short pulse signal VCOMP, the voltage VOUTO, the voltage V_SLOPE and the output signal VDR of the latch also maintain a stable state.

[0028] In the synchronizable adaptive on-time module within a wide frequency range proposed in the present application, the generation of the on-time is not only related to the input voltage and the output voltage, but also realizes the synchronizable function of the switching frequency by introducing the frequency or phase difference information with the external frequency. This not only solves the shortcoming that users cannot customize the switching frequency in traditional adaptive on-time modules, but also can accurately maintain the switching frequency unchanged under stable load conditions. Moreover, because its switching frequency is always synchronized with the external frequency, it is not affected by the nonlinearity and matching accuracy of the circuit.

[0029] Secondly, the additional introduction of current information I_OSC proportional to the external frequency in the on-time generation module can greatly increase the frequency range that can be synchronized. When the input and output voltages are fixed, the ratio of the on-time to the system switching period is the ratio of the output voltage to the input voltage, that is, the higher the switching frequency, the smaller the on-time, and vice versa, the larger the on-time. Therefore, when the variable frequency range required by the user is relatively large, it means that the change in the on-time is also large. At this time, I_OSC is proportional to the variable frequency, that is, I_SLOPE is also proportional to the external frequency, and the on-time generated in this application is inversely proportional to the current of I_SLPOE. Therefore, when the external frequency is higher, the on-time generated by this application is smaller and is in a fixed linear proportion to the external frequency.

[0030] In summary, the present invention introduces an external reference frequency variable to tune the on-time, so that the system switching frequency can be synchronized with the external frequency, and can accurately maintain the switching frequency unchanged when the load is stable, without being affected by the nonlinearity and matching accuracy of the circuit, which is convenient for device selection; moreover, the ramp current generated for the on-time can be inversely proportional to the frequency and phase difference to improve the tuning gain of the on-time, and also improve the range of frequency synchronization, broaden the input and output voltage range of the entire architecture application, reduce the range requirement for the loop control voltage, and greatly reduce the problem of continuous frequency changes and small range due to non-ideal factors of the circuit, which is significantly progressive.

[0031] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. An adaptive on-time generating circuit capable of synchronization within a wide frequency range, used for frequency synchronization between a power supply system and an external system, characterized in that: It includes an external current introduction module, a multiplier, a ramp wave generating circuit, an input sampling circuit, an output sampling circuit, a voltage-to-current circuit 1, an external introduction circuit, a comparator and an SR latch; The external current introduction module is used to receive the switching frequency of the power supply system and the reference frequency of the external system and generate the current I_PHASE, and transmit the current I_PHASE to the IN3 input terminal of the multiplier; the input sampling circuit is used to receive the input voltage VIN and generate the VINO signal, and convert the VINO signal into the current I_VIN through the voltage-to-current circuit 1 and transmit it to the IN1 input terminal of the multiplier; the external introduction circuit adopts the first DC current source to transmit the current I_OSC proportional to the reference frequency to the IN2 input terminal of the multiplier; the output terminal of the multiplier outputs The output end of the multiplier is connected to the ramp wave generating circuit; the ramp wave generating circuit uses the MOS tube to generate a ramp current for controlling the conduction time based on IOUT; the output sampling circuit is connected to the negative input end of the comparator; the output end of the comparator is connected to the ramp wave generating circuit through the SR latch to form a loop, and the SR latch is used to output the conduction time of the MOS tube.

2. The adaptive on-time generating circuit capable of synchronization within a wide frequency range according to claim 1, characterized in that: The external current introduction module includes a frequency detector, a phase detector, a charge pump, a loop filter circuit and a voltage-to-current circuit 2; Among them, the input end of the frequency detector receives the switching frequency of the power supply system and the reference frequency of the external system, and the output end drives the charge pump to generate the control voltage VCTRL; the loop filter circuit is used to perform loop filtering on the control voltage VCTRL; the voltage-to-current circuit 2 converts the control voltage VCTRL after loop filtering into the current I_PHASE.

3. The adaptive on-time generating circuit capable of synchronization within a wide frequency range according to claim 2, characterized in that: The loop filter circuit includes a resistor R6, a capacitor C2 and a capacitor C3. The first end of the resistor R6 is connected in parallel between the charge pump and the voltage-to-current circuit 2. The second end of the resistor R6 is grounded through the capacitor C2. The capacitor C3 is connected in parallel between the capacitor C2 and the ground and between the charge pump and the voltage-to-current circuit 2.

4. The adaptive on-time generating circuit capable of synchronization within a wide frequency range according to claim 1, characterized in that: The ramp wave generating circuit includes a second DC current source, a MOS tube and a capacitor C1, and the capacitor C1 is grounded; the second DC current source receives AVDD power supply and is connected to the output end of the multiplier to generate a sink current I_SLOPE; the sink current I_SLOPE flows through the capacitor C1 to generate a ramp voltage signal V_SLOPE, and the positive input end of the comparator receives the ramp voltage signal V_SLOPE; the drain of the MOS tube is connected between the second DC current source and the capacitor C1, the source of the MOS tube is connected between the capacitor C1 and the ground, and the gate of the MOS tube is connected to the output end of the SR latch.

5. The adaptive on-time generating circuit capable of synchronization within a wide frequency range according to claim 1, characterized in that: The input sampling circuit and the output sampling circuit both adopt a resistor voltage divider structure; the input sampling circuit includes an input voltage VIN, a resistor R1 and a resistor R2 connected in sequence, the resistor R2 is grounded, and the voltage-to-current circuit 1 is connected between the resistor R1 and the resistor R2; the output sampling circuit includes an output voltage VOUT, a resistor R3 and a resistor R4 connected in sequence, the resistor R4 is grounded, and the negative input end of the comparator is connected between the resistor R3 and the resistor R4.

6. The adaptive on-time generating circuit capable of synchronization within a wide frequency range according to claim 1, characterized in that: The voltage-to-current circuit 1 is a resistor-type conversion circuit or an operational amplifier-type conversion circuit.

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