CN116937978A - COT control circuit - Google Patents

COT control circuit Download PDF

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Publication number
CN116937978A
CN116937978A CN202310897132.8A CN202310897132A CN116937978A CN 116937978 A CN116937978 A CN 116937978A CN 202310897132 A CN202310897132 A CN 202310897132A CN 116937978 A CN116937978 A CN 116937978A
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China
Prior art keywords
output
coupled
input
signal
switching converter
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CN202310897132.8A
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Chinese (zh)
Inventor
薛辉
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Rongxin Electronic Technology Wuxi Co ltd
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Rongxin Electronic Technology Wuxi Co ltd
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Priority to CN202310897132.8A priority Critical patent/CN116937978A/en
Publication of CN116937978A publication Critical patent/CN116937978A/en
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0003—Details of control, feedback or regulation circuits
    • H02M1/0006—Arrangements for supplying an adequate voltage to the control circuit of converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices

Abstract

The application discloses a COT control circuit for a switching converter, comprising: a time length control unit including: a voltage-controlled current source whose current is related to an input voltage signal of the switching converter; a voltage divider circuit having an input coupled to an output of the switching converter and an output configured to output a first signal related to the switching converter output signal; a first comparator having a first input coupled to the voltage controlled current source and a second input configured to receive a first signal configured to output a duration control signal; a first capacitor and a first resistor are coupled in series between the voltage-controlled current source and ground, the first end of the first capacitor is also coupled to the first input of the first comparator; a first transistor having a first pole coupled to a first input of the first comparator and a second pole coupled to ground, the control pole configured to receive a control signal related to the COT control circuit output signal; wherein the value of the first resistor is the ratio of the delay time of the switching comparator to the first capacitance value.

Description

COT control circuit
Technical Field
The application belongs to the field of electrical control, and particularly relates to a COT control circuit.
Background
The operation modes of the switching converter mainly include a peak current control mode, a mean current control mode, and a Constant on/off time Control (COT) control mode. These control modes all belong to the PWM control mode. The COT control mode has good transient response and high light load efficiency, and is widely used in switching converters.
In the COT control mode, the existing adaptive COT control mode generates a reference voltage based on the input voltage and the feedback voltage of the switching converter, compares the feedback voltage with the reference voltage to generate a signal for controlling the conduction of the power transistor in the controllable switch of the switching converter, and generates a conduction time for keeping the conduction state of the power transistor by using an internal timing circuit, so that the power transistor in the controllable switch is controlled to be conducted alternately by using a PWM signal. The on-time of the power transistor is determined by the input voltage, the output voltage, the delay time and other factors. Taking input voltage variation as an example, corresponding to different input voltages, in order to maintain volt-second balance of the power inductor, the existing self-adaptive COT control circuit can generate conduction time with different durations, so that the constant switching frequency is ensured. In actual operation, when the switching frequency is higher, because of the influence of delay time of a comparator, a driver and other circuits in the circuit, the switching frequency output by the existing adaptive COT control circuit is lower and lower along with the rise of the input voltage, so that the on time of the power transistor is not kept constant along with the change of the on time, the ripple stability of the circuit is poor, the EMI performance is further influenced, and the complexity of the circuit is increased.
Disclosure of Invention
Aiming at the technical problems in the prior art, the application provides a COT control circuit for a switching converter, which comprises the following components: a time length control unit including: a voltage-controlled current source whose current is related to an input voltage signal of the switching converter; a voltage divider circuit having an input coupled to an output of the switching converter and an output configured to output a first signal related to the switching converter output signal; a first comparator having a first input coupled to the voltage controlled current source and a second input configured to receive the first signal and configured to output a duration control signal; a first capacitor and a first resistor are coupled in series between the voltage controlled current source and ground, the first end of the first capacitor also being coupled to the first input of the first comparator; a first transistor having a first pole coupled to a first input of the first comparator and a second pole coupled to ground, and a control pole configured to receive a control signal related to the COT control circuit output signal; wherein the value of the first resistor is the ratio of the delay time of the switching comparator to the first capacitance value.
In particular, the COT control circuit, wherein the current of the voltage controlled current source is related to an input voltage signal of the switching converter by a factor of n; a second input of the first comparator is configured to receive m times the switching converter output signal, where m and n are both numbers greater than zero and less than 1.
In particular, the COT control circuit further comprises a reference unit, a first input terminal of which is configured to receive an input voltage signal of the switching converter, and a second input terminal of which is configured to receive a feedback signal of the switching converter, configured to generate a reference signal; a comparison unit having a first input configured to receive a feedback signal of the switching converter and a second input coupled to an output of the reference unit to receive the reference signal, configured to operate and compare the two; a logic unit having a first input coupled to the output of the comparison unit and a second input coupled to the output of the duration control unit, configured to generate a PWM signal at its first output that controls the switching converter.
In particular, the COT control circuit, wherein the logic unit is further configured to generate a signal at its second output that is logically opposite to the PWM signal, and the control electrode of the first transistor is coupled to the second output of the logic circuit.
The application also provides a switching converter comprising: a controllable switch module; and a COT control circuit as claimed in any one of the preceding claims coupled thereto.
In particular, the switching converter, wherein the controllable switching module comprises: a first power transistor and a second power transistor coupled in series with each other between a voltage input terminal of the switching converter and ground, a node of the first transistor coupled to a second pole of the second transistor being a switching node; a driving unit, the input end of which is coupled to the output end of the COT control circuit, the first output end and the second output end of which are respectively coupled to the control poles of the first power transistor and the second power transistor, and the driving unit is configured to generate a control signal for controlling the first power transistor and the second power transistor to be alternately conducted based on the PWM signal output by the COT control circuit; a first inductor coupled between the switching node and an output of the switching converter; a first capacitor coupled between the output of the switching converter and ground; a feedback unit coupled between the output of the switching converter and the first input of the COT control circuit.
The application also provides an electronic device comprising a switching converter as described in any one of the preceding.
Drawings
Preferred embodiments of the present application will be described in further detail below with reference to the attached drawing figures, wherein:
FIG. 1 is a schematic circuit diagram of a switching converter section according to one embodiment of the application;
FIG. 2 is a schematic circuit diagram of an adaptive COT control module/circuit according to one embodiment of the application; and
fig. 3 is a schematic timing diagram of a switching converter according to one embodiment of the application.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments of the application. In the drawings, like reference numerals describe substantially similar components throughout the different views. Various specific embodiments of the application are described in sufficient detail below to enable those skilled in the art to practice the teachings of the application. It is to be understood that other embodiments may be utilized or structural, logical, or electrical changes may be made to embodiments of the present application.
Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but are intended to be part of the specification where appropriate. For the purpose of illustration only, the connection between elements in the figures is meant to indicate that at least the elements at both ends of the connection are in communication with each other and is not intended to limit the inability to communicate between elements that are not connected. In addition, the number of lines between two units is intended to indicate at least the number of signals involved in communication between the two units or at least the output terminals provided, and is not intended to limit the communication between the two units to only signals as shown in the figures.
Transistors may refer to transistors of any structure, such as Field Effect Transistors (FETs) or bipolar transistors (BJTs). When the transistor is a field effect transistor, it may be hydrogenated amorphous silicon, metal oxide, low temperature polysilicon, organic transistor, or the like, depending on the channel material. The carriers are electrons or holes, and can be divided into an N-type transistor and a P-type transistor, wherein the control electrode refers to the grid electrode of the field effect transistor, the first electrode can be the drain electrode or the source electrode of the field effect transistor, the corresponding second electrode can be the source electrode or the drain electrode of the field effect transistor, and the control electrode or the third electrode can be the grid electrode; when the transistor is a bipolar transistor, the control electrode refers to the base electrode of the bipolar transistor, the first electrode may be the collector electrode or the emitter electrode of the bipolar transistor, the corresponding second electrode may be the emitter electrode or the collector electrode of the bipolar transistor, and the control electrode or the third electrode may be the base electrode. The transistor may be fabricated using amorphous silicon, polysilicon, oxide semiconductor, organic semiconductor, NMOS/PMOS processes, or CMOS processes.
The application provides a frequency-constant self-adaptive COT control circuit, which can better control the switching frequency by making the on/off time proportional to the input voltage and inversely proportional to the output voltage, and can keep the switching frequency relatively constant when the input voltage and the output voltage change on the basis of ensuring the constant switching frequency when the input voltage and the output voltage are stable.
The application is described below by taking a buck converter as an example, but the application is not to be considered as limited to buck converters. The self-adaptive COT control circuit provided by the application can also be applied to a boost converter and power conversion equipment such as full-bridge type, half-bridge type, isolated DC-DC and the like.
The delay time of the switching converter mentioned in the present application includes delay time due to the controllable switching module and other components.
Fig. 1 is a schematic circuit diagram of a switching converter according to an embodiment of the present application. According to one embodiment, the switching converter comprises at least one controllable switching module 11 and an adaptive COT control module/circuit 12.
According to one embodiment, a first input of the controllable switch module 11 is coupled to an output of the adaptive COT control module 12, configured to receive the PWM control signal output by the adaptive COT control module 12. A second input of the controllable switching module 11 is coupled to a voltage input of the switching converter, receiving an input voltage Vin. The controllable switching module 11 has a first output coupled to the voltage output of the switching converter for outputting the voltage Vout. A second output of the controllable switching module 11 is coupled to a first input of the adaptive COT control module 12.
According to one embodiment, the controllable switching module 11 further comprises a power transistor 112 and a power transistor 113 coupled in series with each other between the voltage input of the switching converter and ground. A first pole of the power transistor 112 receives an input voltage Vin. The gates of the power transistor 112 and the power transistor 113 are coupled to a first output and a second output of the driving unit 110, respectively. The node of the second pole of the power transistor 112 coupled to the first pole of the power transistor 113 is a switching node SW.
According to one embodiment, the controllable switch module 11 comprises a drive unit 110. An input of the driving unit 110 is coupled to an output of the COT control module 12, receiving the PWM signal. The driving unit 110 is configured to generate a control signal for controlling the power transistor 112 to be alternately turned on with the power transistor 113 based on the PWM signal output from the COT control module 12.
According to one embodiment, the controllable switching module 11 may further comprise an inductance 114 coupled between the switching node SW and the output of the switching converter.
According to one embodiment, the controllable switch module 11 further comprises a capacitor 116. A capacitor 116 is coupled between the output of the switching converter and ground.
According to one embodiment, the controllable switching module 11 further comprises a feedback unit 115 coupled between the output of the switching converter and the first input of the adaptive COT control module 12. The feedback unit 115 is configured to generate a feedback voltage Vfb based on the output voltage Vout or to generate a feedback current Ifb based on the current IL flowing through the inductor 114. In some embodiments, the feedback unit 115 may also be configured to sample the output voltage Vout and the inductor current IL, thereby generating the feedback voltage Vfb or the feedback current Ifb.
According to one embodiment of the application, the first input of the adaptive COT control module 12 receives the feedback voltage Vfb output by the controllable switching module 11. In some embodiments, the first input of the adaptive COT control module 12 may also receive the feedback current Ifb. A second input of the adaptive COT control module 12 receives the input voltage Vin of the switching converter and a third input thereof receives the output voltage Vout of the switching converter. The adaptive COT control module 12 is configured to generate a constant frequency PWM signal controlling the alternating conduction of the power transistor 112 and the power transistor 113 by comparing and calculating the input voltage of the switching converter, the feedback voltage or feedback current output by the controllable switching module 11, and the output voltage of the switching converter.
According to one embodiment, the adaptive COT control module 12 may be packaged together with other devices in the controllable switch module 11, except for the inductor 114 and the capacitor 116, within the same chip. According to another embodiment, the adaptive COT control module 12 may also be implemented as an off-chip control module that is packaged separately, providing PWM signals for a switching converter or other device.
Fig. 2 is a schematic circuit diagram of an adaptive COT control module/circuit according to an embodiment of the present application.
According to one embodiment of the application, the adaptive COT control module 22 comprises a reference unit 221, a first input terminal of which receives the input voltage Vin of the switching converter, a second input terminal of which receives the feedback voltage Vfb output by the controllable switching module, and an output terminal of which is coupled to a second input terminal of the comparison unit 223. The reference unit 221 is configured to generate a reference voltage Vref1 according to an input voltage Vin and a feedback voltage Vfb. In some embodiments, the comparison unit 223 may also generate the reference voltage Vref1 based only on the input voltage Vin.
According to one embodiment, the adaptive COT control module 22 comprises a comparison unit 223, a first input of which receives the feedback voltage Vfb output by the switching converter, and an output of which is coupled to a first input of the logic unit 225. According to another embodiment of the present application, the first input of the comparing unit 223 may also receive the feedback current Ifb output by the switching converter. The comparison unit 223 is configured to calculate and compare the feedback voltage Vfb and the reference voltage Vref1 to generate a SET signal SET.
According to one embodiment, the SET signal SET is a pulse signal. According to one embodiment, when the current IL flowing through the inductor 114 reaches the valley value, the feedback voltage Vfb output by the feedback 115 is lower than the reference voltage Vref1, and the SET signal SET output by the comparing unit 223 is a pulse signal.
According to one embodiment, the adaptive COT control module 22 includes a duration control unit 227. The first input terminal of the duration control unit 227 receives the input voltage Vin of the switching converter, the second input terminal thereof receives the output voltage Vout of the switching converter, the third input terminal thereof is coupled to the second output terminal of the logic unit 225, and the output terminal thereof is coupled to the second input terminal of the logic unit 225. The duration control unit 227 is configured to generate a duration control signal RST for controlling the on-state duration of the high-side power transistor in the controllable switch module based on the input voltage Vin, the output voltage Vout, and the driving signal DRV generated by the logic unit 225.
According to one embodiment of the application, the duration control unit 227 includes a voltage controlled current source 2271. An input of the voltage controlled current source 2271 receives the input voltage Vin of the switching converter and an output thereof is coupled to a negative input of the comparator 2272. In some embodiments, voltage controlled current source 2271 may also include, for example, a MOSFET voltage controlled current source device.
According to one embodiment, when the switching converter input voltage is Vin, the voltage controlled current source 2271 outputs a current that is n times the magnitude of the input voltage Vin in response to the input voltage. The value of n is controlled by the amplifying capability of the voltage controlled current source 2271. In one embodiment of the present application, n is a number in the range of greater than zero and less than 1.
According to one embodiment, duration control module 227 includes a comparator 2272 having an output coupled to a second input of logic unit 225. The comparator 2272 is configured to provide the duration control signal RST to the logic unit 225.
According to one embodiment, the duration control module 227 includes a voltage divider circuit 2277. An input of the voltage divider circuit 2277 receives the output voltage Vout of the switching converter, and an output thereof is coupled to the positive input of the comparator 2272. According to one embodiment, the voltage divider circuit 2277 includes voltage divider resistors. The voltage dividing circuit 2277 is configured to output the reference voltage Vref2 according to the output voltage Vout of the switching converter.
According to one embodiment, the node of voltage controlled current source 2271 coupled to the negative input of comparator 2272 is node a. When the node a potential is lower than the reference voltage Vref2, the duration control signal output by the comparator 2272 is low (e.g., 0); when the potential of the node a is higher than the reference voltage Vref2, the duration control signal RST output from the comparator 2272 is a pulse signal (for example, 1).
According to one embodiment, the reference voltage Vref2 is m times Vout in size. According to one embodiment, the value of m is related to the resistance value of the voltage dividing resistor, and the value of m ranges from a number greater than zero to less than 1.
In particular, according to one embodiment of the application, the duration control unit 227 further comprises a capacitor 2273 and a resistor 2275 coupled in series with each other between the output of the voltage controlled current source 2271 and ground.
In some embodiments, the output of voltage controlled current source 2271 is coupled to one end of resistor 2275, one end of capacitor 2273 is coupled to resistor 2275, and the other end of capacitor 2273 is coupled to ground. A second pole of transistor 2276 is coupled to a node between capacitor 2273 and capacitor 2275.
According to another embodiment of the application, resistor 2275 may also be located outside of adaptive COT control module 12 and not packaged within the same integrated circuit as the other units in the adaptive COT control module.
According to one embodiment, the duration control unit 227 may also include a transistor 2276. A second pole of the transistor 2276 is coupled to the node a, a first pole thereof is grounded, and a control pole thereof is coupled to a second output terminal of the logic unit 225 for receiving the driving signal DRV. According to one embodiment, transistor 2276 may be an N-type MOSFET. In some embodiments, the control electrode of transistor 2276 is coupled to a second output of logic cell 225. In other embodiments, the control electrode of transistor 2276 may be coupled to a first output of logic cell 225 through an NOT gate.
According to one embodiment, when the drive signal DRV is active, the transistor 2276 is turned on and the capacitor 2273 is discharged through the transistor 2276. When the drive signal DRV fails, the transistor 2276 is turned off and the capacitor 2273 is charged.
According to one embodiment, the adaptive COT control module 22 includes a logic unit 225. A first output of the logic unit 225 is coupled to an output of the adaptive COT control module 22, outputting a PWM signal that controls the switching converter. According to one embodiment, the logic 225 may be an RS flip-flop. The logic unit 225 is configured to perform a logic operation on the SET signal SET and the duration control signal RST, and generate a PWM signal for controlling the state of the controllable switch module and a driving signal DRV for controlling the on/off of the transistor 2276.
In some embodiments, when the SET signal SET is active, the PWM signal output by the logic unit 225 transitions from a low level to a high level; the duration control signal RST determines the pulse width of the PWM signal. In some embodiments, the driving signal DRV is an inverse logic signal of the PWM signal.
In the existing self-adaptive COT control module, a duration control moduleOnly a capacitance is coupled between the intermediate node a and ground. When the PWM signal generated by the logic unit jumps from low level to high level, the capacitor between the node A and the ground in the duration control unit starts to charge, when the potential of the node A reaches mVout level, the self-adaptive COT control module outputs the PWM signal to jump from high level to low level, and the driving unit controls the high-side power transistor in the controllable switch module to be turned off and simultaneously the low-side power transistor to be turned on. The pulse width of PWM is equal to the time that the potential of node A reaches the mVout level from zero, expressed asWherein C is the capacitance coupled between node A and ground.
PWM control-based buck converter, whose on-time versus period can be expressed asWherein T is ON For the on time of the high side power transistor, T is the switching period.
In an ideal case, the time for the potential of node a to reach the mvut level from zero is the pulse width of the PWM output by the adaptive COT control module, then,let C>I.e. the switching period is related to the values of capacitance, m and n.
However, in practical applications, the driving unit of the controllable switch module, the comparing unit of the adaptive COT control module, and the driving unit of the controllable switch module all have transmission delay time, so that the on/off time of the high-side power transistor has delay. Assuming that the total delay time of each cell is Tdelay, the actual on-time of the high-side power transistor can be expressed as T ON ＝T ON1 +tdelay. That is, the switching period is affected by the delay time.
The existing self-adaptive COT control circuit ignores the influence of delay time, when the switching frequency is low, the total delay time Tdelay of each unit is far smaller than the switching period T, and when factors such as input voltage, output voltage and the like change, the change of the switching frequency is not obvious. However, in an application scenario with a high switching frequency, the influence of Tdelay on the switching period is not negligible, and as the input voltage Vin increases, the switching frequency decreases rapidly. At higher switching frequencies, the input voltage range of the switching converter controlled by existing adaptive COT control circuits is limited in order to reduce frequency losses.
In the present application, as shown in fig. 2, a resistor 2275 is included in addition to a capacitor 2273 coupled between the node a of the duration control unit and ground. When the transistor 2276 is turned off, the time when the voltage-controlled current source 2271 charges the capacitor 2273 to bring the node A potential to the level of the reference voltage Vref2 is expressed as
In practical application, on the basis of keeping the original on-time of the high-side power transistor unchanged, the on-time of the high-side power transistor is expressed as T ON ＝T ON2 +Tdelay, i.e. T ON ＝T ON2 +Tdelay-RC, therefore, the resistance R of the resistor 2275 is designed to make the delay time Tdelay equal to the RC value, so that the cancellation of the delay time by the circuit can be realizedThe period of the PWM signal generated by the adaptive COT control module is not changed along with the input voltage, so that the switching frequency has good stability, and the input voltage range which can be received by the switching converter is wider.
According to one embodiment of the application, the formula is followedThe value of the switching period T is obtained according to actual design requirements; the value of the capacitor 2273 is set according to actual design requirements, so that the capacitor 2273 is not easy to be excessively designed; specific values of m and nThe switching frequency is designed to be dependent.
In some embodiments, the value of Tdelay may be obtained through simulation or testing.
According to one embodiment, the value of the resistor 2275 is calculated according to the switching frequency and the delay time Tdelay, so as to cancel the delay time.
According to one embodiment of the application, after the switching period T is set, the capacitor 2273 and the resistor 2275 are integrated into the adaptive COT control module, and the adjustment of the switching frequency can be achieved by adding an off-chip amplifying circuit to adjust the values of m and n.
Fig. 3 is a schematic timing diagram of a switching converter according to one embodiment of the application.
In fig. 3, the solid line represents the time domain diagrams of each signal of the conventional COT control module, and the dotted line represents the time domain diagrams of each signal of the adaptive COT control module of the present application.
(1) time t1-t2
At time t1, the inductor current IL reaches a valley value, and the comparison unit 223 in the adaptive COT control module outputs a pulse signal as the SET signal SET in response to the change of the feedback voltage Vfb. In the time length control unit 227, since the node a potential is lower than the value of the reference voltage Vref2, the comparator 2272 outputs the time length control signal RST which is still at the low level. At this time, the first output terminal of the logic unit 225 outputs the PWM signal to transition from the low level to the high level, and the second output terminal outputs the driving signal DRV to transition from the high level to the low level.
In the controllable switch module, the driving unit 110 receives the high-level PWM signal to drive the high-side power transistor 112 to be turned on, and the low-side power transistor 113 to be turned off. The voltage at the switch node SW reaches the input voltage Vin and the current IL flowing through the inductor 114 gradually rises.
In the duration control unit 227, the transistor 2276 receives the DRV signal and is turned off. At this time, the voltage controlled current source 2271 starts to charge the capacitor 2273, and the node a potential gradually rises from the VR level. VR is the voltage across resistor 2275.
After time t1, during times t1-t2, both the SET signal SET and the duration control signal RST remain low, and the first output of the logic unit 225 outputs a signal that remains in the previous state, maintaining the PWM signal at a high level.
(2) time t2-t3
At time t2, the current IL flowing through the inductor 114 reaches the peak value, the feedback voltage Vfb received by the comparing unit 223 in the adaptive COT control module is higher than the reference voltage Vref1, and the SET signal SET still at the low level is output. The potential of the node a in the time length control unit 227 is higher than the mVout level, and the comparator 2271 outputs the time length control signal RST as a pulse signal. A first output of the logic unit 225 outputs a PWM signal that transitions from a high level to a low level (e.g., 0). Conversely, the second output terminal of the logic unit 225 outputs a DRV signal that transitions from a low level to a high level.
In the controllable switching module, the driving unit receives the PWM signal from the high level to the low level, the high side power transistor 112 is turned off, and the low side power transistor 113 is turned on. The voltage at the switching node SW drops to zero and the current IL through the inductor 114 gradually drops from a peak value to a valley value at time t 3.
In the duration control unit 227, the transistor 2276 receives the DRV signal to turn on, and the branch of the resistor 2275 connected in series with the capacitor 2273 is coupled to the ground through the transistor 2276, and the node a potential drops to zero.
After time t2, during times t2-t3, both the SET signal SET and the duration control signal RST remain low, and the first output terminal of the logic unit 225 outputs the PWM signal at a low level.
As shown by the solid line in fig. 3, the high-side power transistor 112 is turned off at t3' according to each signal time domain curve of the conventional adaptive COT control module, so that the turn-off time of the high-side power transistor 112 is delayed by Tdelay compared to the turn-off time t2 of the adaptive COT control module of the present application, thereby affecting the switching frequency. According to the self-adaptive COT control module provided by the application, the potential of the node A at the time t1 is improved, so that the time for the potential of the node A to reach mVout is advanced from t2 to t2', and the influence caused by delay time is counteracted.
Table 1 shows simulation data of the COT control circuit according to the present application applied to the switching converter shown in fig. 1.
In this embodiment, the output voltage is 5V fixed, and the input voltage Vin varies in the range of 8V-64V. In the buck converter configuration shown in fig. 1, the capacitance c=2.5pf, m=2m, n=10. The total delay time tdelay=20ns of the sum of the comparison unit delay and the drive unit delay and the like. The calculation results in c×m/n=500n, i.e. the desired switching period is 500ns, corresponding to a switching frequency of 2MHz.
By using the self-adaptive COT switch control device provided by the application, the resistance value R=Tdelay/C=8kΩ of the resistor of the control unit is designed. The results shown in Table 1 were obtained by simulation test.
In response to different input voltage values, the switching period of the PWM signal output by the frequency-fixed adaptive COT control circuit is kept constant all the time, and the switching frequency (Fsw) is also kept constant.
TABLE 1 simulation values for the adaptive COT control module/circuit of the present application
The existing self-adaptive COT control circuit is adopted to control the controllable switch module, and the numerical values shown in the table 2 can be obtained through simulation test.
Table 2 simulation values using existing adaptive COT control circuits
When the switching frequency is high, the switching frequency (Fsw) is different when the switching period of the PWM signal output by the existing adaptive COT control device is different from the input voltage value. When the switching frequency is set at a high frequency, the switching frequency is greatly affected when the input voltage is changed from low to high because the delay time occupies a relatively large amount in the switching period.
The COT control circuit provided by the application inherits the working principle and characteristics of the existing self-adaptive COT control circuit. The input voltage and the output voltage are converted and then are associated with the conduction time, so that when the input voltage and the output voltage of the circuit change in a wider range, the compensation resistor is added in the duration control unit to offset the switch delay, and the switch converter can work at high frequency more stably, thereby reducing the size of a filter element and avoiding the EMI sensitive frequency band.
The application also provides a switching converter which comprises the COT control module/circuit.
The application also provides electronic equipment which can comprise the switching converter in the embodiment of the application.
The above embodiments are provided for illustrating the present application and not for limiting the present application, and various changes and modifications may be made by one skilled in the relevant art without departing from the scope of the present application, therefore, all equivalent technical solutions shall fall within the scope of the present disclosure.

Claims (7)

1. A COT control circuit for a switching converter, comprising:
a time length control unit including:
a voltage-controlled current source whose current is related to an input voltage signal of the switching converter;
a voltage divider circuit having an input coupled to an output of the switching converter and an output configured to output a first signal related to the switching converter output signal;
a first comparator having a first input coupled to the voltage controlled current source and a second input configured to receive the first signal and configured to output a duration control signal;
a first capacitor and a first resistor are coupled in series between the voltage controlled current source and ground, the first end of the first capacitor also being coupled to the first input of the first comparator;
a first transistor having a first pole coupled to a first input of the first comparator and a second pole coupled to ground, and a control pole configured to receive a control signal related to the COT control circuit output signal;
wherein the value of the first resistor is the ratio of the delay time of the switching comparator to the first capacitance value.
2. The COT control circuit of claim 1, wherein the current of the voltage controlled current source is related to an input voltage signal of the switching converter by a factor of n; a second input of the first comparator is configured to receive m times the switching converter output signal, where m and n are both numbers greater than zero and less than 1.
3. The COT control circuit of claim 1, further comprising
A reference unit having a first input configured to receive an input voltage signal of the switching converter and a second input configured to receive a feedback signal of the switching converter, configured to generate a reference signal;
a comparison unit having a first input configured to receive a feedback signal of the switching converter and a second input coupled to an output of the reference unit to receive the reference signal, configured to operate and compare the two;
a logic unit having a first input coupled to the output of the comparison unit and a second input coupled to the output of the duration control unit, configured to generate a PWM signal at its first output that controls the switching converter.
4. The COT control circuit of claim 3, wherein the logic unit is further configured to generate a signal at a second output thereof that is logically opposite the PWM signal, and the control electrode of the first transistor is coupled to a second output of the logic circuit.
5. A switching converter, comprising:
a controllable switch module; and a COT control circuit as claimed in any one of claims 1 to 4 coupled thereto.
6. The switching converter of claim 5, wherein the controllable switching module comprises:
a first power transistor and a second power transistor coupled in series with each other between a voltage input terminal of the switching converter and ground, a node of the first transistor coupled to a second pole of the second transistor being a switching node;
a driving unit, the input end of which is coupled to the output end of the COT control circuit, the first output end and the second output end of which are respectively coupled to the control poles of the first power transistor and the second power transistor, and the driving unit is configured to generate a control signal for controlling the first power transistor and the second power transistor to be alternately conducted based on the PWM signal output by the COT control circuit;
a first inductor coupled between the switching node and an output of the switching converter;
a first capacitor coupled between the output of the switching converter and ground;
a feedback unit coupled between the output of the switching converter and the first input of the COT control circuit.
7. An electronic device comprising a switching converter according to any of claims 5-6.
CN202310897132.8A 2023-07-20 2023-07-20 COT control circuit Pending CN116937978A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202310897132.8A CN116937978A (en) 2023-07-20 2023-07-20 COT control circuit

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202310897132.8A CN116937978A (en) 2023-07-20 2023-07-20 COT control circuit

Publications (1)

Publication Number Publication Date
CN116937978A true CN116937978A (en) 2023-10-24

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
CN202310897132.8A Pending CN116937978A (en) 2023-07-20 2023-07-20 COT control circuit

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Country Link
CN (1) CN116937978A (en)

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