TWI678063B - Constant on-time controller and buck converter using the same - Google Patents

Abstract

A constant on-period controller for controlling the off-period and on-period of a buck regulator includes a comparator, an on-timer, a reference voltage controller, and a switching device. The comparator is used to compare the feedback voltage generated based on the output voltage of the buck regulator with a reference voltage to generate a termination shutdown signal for termination shutdown. The start-up timer determines the start-up period according to the input voltage and output voltage of the buck regulator, and generates a stop-on signal for terminating the start-up period accordingly. The reference voltage controller is electrically connected to the comparator, and generates a reference voltage according to the feedback voltage and a predetermined voltage. The switching device is electrically connected to the reference voltage controller. At the beginning of the off period, the reference voltage is pulled down to the node voltage of the electronic switching device of the buck regulator.

Description

Controller and step-down converter using it during constant on

The present invention relates to a controller for a buck converter, and more particularly to a constant on-time controller and a buck converter using the constant on-time controller.

The on-time controller can be used to control the on-time and off-time of the buck regulator. When the step-down regulator is turned on (ie, during the on period), the input voltage will charge and store the energy storage inductor of the step-down regulator through the opening of the electronic switching device (for example, a switching transistor) of the step-down regulator. Yes, and an output voltage related to the input voltage is generated at the output of the buck regulator. When the step-down regulator is turned off (ie, during the shutdown period), because the electronic switching device of the step-down regulator is turned off, the input voltage is isolated from the energy storage inductor and output of the step-down regulator. The energy inductor transmits the stored energy to the output of the buck regulator to provide the output voltage of the buck regulator.

One of the existing on-period controllers is a constant-on period controller, which is used to provide a constant-on period. When the output voltage of the step-down regulator is lower than the reference voltage, the controller step-down regulator enters the on-period, that is, the off-period of the step-down regulator ends. Then, after the buck regulator is continuously turned on for a constant on period, it enters the off period. Constant opening period control The controller has a circuit that determines the constant on-time by the input voltage and the output voltage. Therefore, the buck regulator is turned on at a constant frequency even if the duty cycle is changed. Generally speaking, the ripple of the output voltage of the buck regulator is mainly determined by the ripple current of the equivalent series resistance of the storage inductor flowing into the output inductor. In application, a multilayer ceramic capacitor (MLCC) with a lower equivalent series impedance can be selected as the output capacitor, so that the ripple of the output voltage of the buck regulator is relatively small.

An embodiment of the present invention provides a controller during a constant on period and a buck converter using the same to solve the problem that when the ripple of the output voltage of the buck regulator is relatively small, the controller is prone to noise influence during the constant on period and reduces its stability Sexual technical issues.

To achieve the above object, the constant on-period controller provided by the embodiment of the present invention can be used to control the off-period and the on-period of the buck regulator, and includes a comparator, an on-timer, a reference voltage controller, and a switch switching device. The comparator is used to compare the feedback voltage generated based on the output voltage of the buck regulator with a reference voltage to generate a termination shutdown signal for termination shutdown. The start-up timer determines the start-up period according to the input voltage and output voltage of the buck regulator, and generates a stop-on signal for terminating the start-up period accordingly. The reference voltage controller is electrically connected to the comparator, and generates a reference voltage according to the feedback voltage and a predetermined voltage. The switching device is electrically connected to the reference voltage controller. At the beginning of the off period, the reference voltage is instantly pulled down to the node voltage of the electronic switching device of the buck regulator. The switching device provides the ground voltage as the reference voltage during the opening period. And a reference voltage that provides the node voltage as a reference voltage during the shutdown period.

Optionally, the switch switching device includes a first switch and a second switch, wherein a first terminal of the first switch and a first terminal of the second switch are electrically connected to a reference voltage controller, and a second terminal of the first switch is connected to the first switch. The second ends of the two switches are respectively electrically grounded and the node voltage, and the first switch and the second switch are turned on in response to the termination-off signal and the termination-on signal, respectively.

Optionally, the reference voltage controller includes an error amplifier, an RC compensation circuit, a transconductance amplifier, and a current sensing resistor. The error amplifier is used to output an error amplification signal according to the feedback voltage and a predetermined voltage. The RC compensation circuit is electrically connected to the output terminal of the error amplifier to reduce the phenomenon of high frequency oscillation. The transconductance amplifier is electrically connected to the output terminal of the error amplifier, and is used to convert the error amplified signal after passing the RC compensation circuit into a current signal. The current sensing resistor is electrically connected between the output terminal of the error amplifier and the switching device, and is used to convert the current signal into a reference voltage.

Optionally, the reference voltage controller further includes a ramp signal generator and an adder. The ramp signal generator is used to generate a ramp signal. The adder is electrically connected to the output end of the transconductance amplifier, the output end of the ramp signal generator and the comparator, and is used to superpose the ramp signal to the current signal.

Optionally, the controller further includes two switches during the constant on period. The two switches are electrically connected to the positive input terminal and the negative input terminal of the comparator, respectively, and are controlled by the termination on signal, so that the comparator performs comparison only during the off period.

Optionally, the controller further includes an RS flip-flop during the constant on period. The RS flip-flop is electrically connected to a comparator, an on-timer, and a step-down regulator, and is used for receiving a termination-off signal and a termination-on signal to generate a control signal and a reverse control signal.

Optionally, the controller further includes a voltage divider during the constant on period. The voltage divider is electrically connected to the reference voltage controller, the comparator, and the step-down regulator to generate a feedback voltage according to the output voltage.

In order to achieve the above object, the step-down converter according to the embodiment of the present invention includes one of the controller and the step-down regulator during the constant turn-on period described above.

In summary, the controller and the step-down converter provided in the constant-on period provided by the embodiment of the present invention have higher noise tolerance and faster response speed.

In order to further understand the features and technical contents of the present invention, please refer to the following detailed description and accompanying drawings of the present invention, but these descriptions and attached drawings are only used to illustrate the present invention, not the right to the present invention No limitation on scope.

1, 1’‧‧‧ Buck Converter

10‧‧‧ Buck Regulator

101‧‧‧ pre-driver circuit

11, 11’‧‧‧ Controller during constant opening

111‧‧‧Divider

112‧‧‧Start timer

113‧‧‧RS Flip-Flop

114‧‧‧ Comparator

115‧‧‧reference voltage controller

1151‧‧‧Error Amplifier

1152‧‧‧Transduction Amplifier

1153‧‧‧ Ramp signal generator

116‧‧‧Switching device

ADD1‧‧‧ Adder

C1, C _F ‧‧‧ Capacitance

C _O ‧‧‧ Output Capacitance

L _X ‧‧‧ Energy storage inductor

NM1, PM1‧‧‧ Transistors

I _SW ‧‧‧node current

R _FBH , R _FBL , R1, R2, R _F ‧‧‧ resistance

R _LOAD ‧‧‧ load resistance

S1 ~ S4‧‧‧‧Switch

T _OFF ‧‧‧ Terminate the shutdown signal

V _FB ‧‧‧Feedback voltage

V _IN ‧‧‧ Input voltage

V _OUT ‧‧‧ Output voltage

V _REFX ‧‧‧ Reference voltage

V ' _REFX ‧‧‧ Voltage on the positive input of the comparator

V _SW ‧‧‧node voltage

R‧‧‧ reset input

S‧‧‧setting input

Q‧‧‧ Positive output

QB‧‧‧Reverse output

RAMP_SIG‧‧‧ Ramp signal

In order to more clearly explain the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some of the present invention. For those of ordinary skill in the art, other embodiments may be obtained based on these drawings without paying creative labor. The drawings of the present invention are briefly explained as follows: FIG. 1 is a schematic diagram of a step-down converter according to an embodiment of the present invention; FIG. 2 is a schematic diagram of a reference voltage controller of a constant-on period controller according to an embodiment of the present invention; FIG. 2 is a waveform diagram of a node voltage, a node current, a reference voltage, and a feedback voltage in a step-down converter of a controller during a constant on period; FIG. 4 is a schematic diagram of a step-down converter according to another embodiment of the present invention; and FIG. 5 is a waveform diagram of the node voltage, the node current, the voltage on the positive input terminal of the comparator and the feedback voltage in the step-down converter using the controller in the constant on period of FIG. 4.

An embodiment of the present invention provides a controller during a constant on period and a buck converter using the same. The controller is configured to widen a difference between a feedback voltage and a reference voltage during the constant on period, thereby expanding noise margin ( noise margin). In this way, when the ripple of the output voltage of the buck regulator is relatively small, the technical problem that the controller is easily affected by noise during the constant turn-on period and reduces its stability can be solved.

Further, the constant-on period controller includes an on-timer, a comparator, a reference voltage controller, and a switching device, wherein the reference voltage controller is electrically connected to the comparator and the switching device. The on timer is used to determine the on period according to the received voltage and the output voltage, and thereby output a termination on signal to terminate the on period. The reference voltage controller compares a feedback voltage generated based on the output voltage with a predetermined voltage to generate a reference voltage. The switching device switches to the ground voltage and the node voltage of the electronic switching device of the buck regulator according to the termination on signal and the termination off signal, so that at the beginning of the off period, the reference voltage is pulled down momentarily to increase the feedback voltage and Difference between reference voltages. During the shutdown period, the pulled down reference voltage will gradually rise to a predetermined voltage and the feedback voltage will gradually decrease. When the feedback voltage is lower than the reference voltage, the comparator will output a termination shutdown signal to terminate the shutdown period.

In the embodiment of the present invention, the reference voltage controller may further include a ramp signal generator. The ramp signal generator can further pull down the reference voltage through the generated ramp signal, and adjust the rising slope of the pull down reference voltage. In this way, in addition to further reducing the sensitivity of the controller to noise and maintaining its stability during constant on, it can further solve the technical problem of the controller's insufficient stability due to signal jitter during constant on. .

The above is the inventive concept of the constant on period controller provided by the present invention and the buck converter using the same. The following will further describe the differences between the constant on period controller and the buck converter using the same in conjunction with the drawings. Implementation and functions and details of each element.

First, please refer to FIG. 1, which is a schematic diagram of a buck converter according to an embodiment of the present invention. The step-down converter 1 includes a step-down regulator 10 and a constant-on period controller 11, wherein the step-down regulator 10 is electrically connected to the constant-on period controller 11. The buck regulator 10 is controlled by the controller 11 during a constant on period, and turned on during the on period, and turned off during the off period. The constant-on period provided by the controller 11 is a constant-on period, and the constant-on period is determined by the input voltage V _IN and the output voltage V _OUT . When the buck regulator 10 is turned on, the input voltage V _IN charges the energy storage inductor L _X of the buck regulator 10 and generates an output voltage V _OUT related to the input voltage V _IN . When the buck regulator 10 is turned off, the input voltage V _IN is isolated from the energy storage inductor L _X and the output of the buck regulator 10, the energy storage inductor L _{X is} discharged, and an output voltage V _OUT is generated accordingly.

Further, the controller 11 generates a termination-on signal at the end of the constant-on period, so that the step-down regulator 10 is controlled to enter a closed period. During the off period, the controller 11 compares the feedback voltage V _FB generated by the output voltage V _OUT of the step-down regulator 10 with the reference voltage V _REFX during the constant on period to generate the termination off signal T _OFF during the termination off period, so that the control The step-down regulator 10 enters an on period. During the turn-on period, the reference voltage V _REFX generated by the controller 11 during the constant turn-on period is a predetermined voltage, but at the end of the turn-on period and the beginning of the turn-off period (that is, when a termination turn-on signal is generated), the controller 11 will The generated reference voltage V _{REFX is} instantly _pulled down to the node voltage V _SW of the electronic switching device of the buck regulator 10, and then, the reference voltage V _REFX gradually rises to a predetermined voltage during the off period. In this way, the noise margin can be extended by the method of instantly pulling down the reference voltage V _REFX to the node voltage V _SW at the beginning of the off period, so that the ripple of the output voltage V _OUT of the buck regulator 10 is relatively small. The technical problem that the controller 11 is susceptible to noise and affects its stability during the constant opening period. On the other hand, optionally, the controller 11 may generate a ramp signal during the off period, and change the slope of the reference voltage V _REFX through the ramp signal to further solve the controller 11 ’s jitter due to the signal during the constant on period ( jitter) and insufficient technical stability.

The implementation manner of the step-down regulator 10 is described below, but the implementation manner of the step-down regulator 10 described below is not intended to limit the present invention, and the step-down regulator 10 may have other types of implementation manners.

Embodiment, the buck regulator 10 includes a pre-driver (pre-driver) circuit 101, a switching transistor for switching the electronic device PM1, NM1, inductor L _X, the output capacitance and the load resistance R C _O thereto _LOAD . The pre-driver circuit 101 is electrically connected to the controller 11 during the constant on period. The gates of the switching transistors PM1 and NM1 are electrically connected to the pre-driver circuit 101. The source of the switching transistor PM1 receives the input voltage V _IN and the source of the switching transistor NM1 The pole is coupled to the ground voltage, and the drains of the switching transistors PM1 and NM1 are electrically coupled to one end of the energy storage inductor L _X , and the other end of the energy storage inductor L _X is coupled to the load resistor R _OLOAD through the output capacitor C _{O in} parallel with each other. Connected to ground voltage and used as the output terminal of the buck regulator 10 (also the output terminal of the buck converter 1) to output the output voltage V _OUT . In addition, the voltages on the drains of the switching transistors PM1 and NM1 are the node voltage V _SW of the aforementioned electronic switching device.

The pre-driver circuit 101 receives control signals related to the termination-off signal T _OFF and the termination-on signal, and generates a gate control signal to control the opening and closing of the switching transistors PM1 and NM1. The pre-driver circuit 101 may include a plurality of logic gates. Logic circuit, but the present invention is not limited thereto. In this embodiment, the switching transistors PM1 and NM1 are respectively a PMOS transistor and an NMOS transistor, but the present invention is not limited thereto.

When the controller 11 generates a termination shutdown signal T _OFF during the constant on period, the control signal has a logic high level voltage. Thus, the pre-driver circuit 101 controls the PMOS transistor and the NMOS transistor to turn on according to the control signal, so that the input voltage V _IN charges the energy storage inductor L _X and generates an output voltage V _OUT associated with the input voltage V _IN at the output terminal. When the controller 11 is turned on during the constant to produce a stop signal is turned on, the control signal has a logic low level voltage, so the pre-driver circuit 101 in accordance with a control signal to control PMOS transistor and the NMOS transistor is closed to the inductor L _X of The output is discharged to generate an output voltage V _OUT at the output. Furthermore, the output voltage V _OUT gradually increases during the on period, and the output voltage V _OUT gradually decreases during the off period.

The implementation of the controller 11 during the constant on period is described below, but the implementation of the controller 11 during the constant on period is not intended to limit the present invention, and the controller 11 may have other types of implementations.

The controller 11 includes a voltage divider 111, an on-timer 112, an RS register 113, a comparator 114, a reference voltage controller 115, and a switch switching device 116 during the constant on period. The voltage divider 111 is electrically connected to the output terminal of the step-down regulator 10 to receive the output voltage V _OUT . The reference voltage controller 115 and the comparator 114 are electrically connected to the voltage divider 111. The switching device 116 is electrically connected to the RS register 113 and the reference voltage controller 115. The RS register 113 is electrically connected to the comparator 114, the on-timer 112, and the pre-driver circuit 101 of the buck regulator 10.

Divider 111 for generating the feedback voltage V _FB to the output voltage V _OUT, the voltage divider 111 may be implemented by a plurality of resistors R _FBH and R _FBL, wherein one end of the resistor R _FBH receives the output voltage V _OUT, the resistor R _FBH The other end is electrically connected to one end of the resistor R _FBL to output a feedback voltage V _FB , and the other end of the resistor R _FBL is electrically connected to a ground voltage. The start-up timer 112 is used to receive the input voltage V _IN and the output voltage V _OUT and determine a constant on-time based on the input voltage V _IN and the output voltage V _OUT . After the buck regulator 10 is turned on for a period of on-time, the output is used for To terminate the open signal during the open period. The on-timer 112 may be a one-shot on-timer, but the present invention is not limited thereto.

The reset input terminal R and the setting input terminal S of the RS flip-flop 113 respectively receive a termination on signal and a termination off signal T _OFF , and the control signal output from the positive output terminal Q of the RS flip-flop 113 and the reverse output QB output. The level of the reverse control signal is determined according to the termination on signal and the termination off signal T _OFF . Further, when the termination enable signal is a logic high level, the levels of the control signal output from the positive output terminal Q of the RS flip-flop 113 and the reverse control signal output from the reverse output terminal QB are the logic low level and Logic high level; when the T _OFF signal is closed, it is logic high level. The levels of the control signal output from the positive output terminal Q of the RS flip-flop 113 and the reverse control signal output from the reverse output terminal QB are logic high. Level and logic low level.

The positive and negative inputs of the comparator 114 receive the reference voltage V _REFX and the feedback voltage V _{FB respectively} , and compare the reference voltage V _REFX and the feedback voltage V _{FB so} that the feedback voltage V _{FB is} lower than the reference voltage V _REFX At this time, the termination shutdown signal T _OFF during the termination shutdown is generated. The reference voltage controller 115 receives the feedback voltage V _FB and generates an error amplification signal between the feedback voltage V _FB and a predetermined voltage. Then, the reference voltage controller 115 converts the error amplified signal into a current signal. After that, the reference voltage controller 115 converts the current signal into a reference voltage V _REFX through a resistor. Please note that, optionally, the reference voltage controller 115 may superimpose a ramp signal to a current signal to solve the technical problem of signal jitter, but the present invention is not limited thereto.

The switching device 116 is configured to provide a ground voltage as a baseline voltage during an on period and a node voltage V _SW as a reference voltage during an off period. In this way, at the beginning of the off period, the reference voltage V _REFX is pulled down to the node voltage V _SW momentarily, and then gradually rises to a predetermined voltage. The switch switching device 116 may be implemented by two switches S1 and S2, but the invention is not limited thereto. One end of switch S1 is electrically connected to reference voltage controller 115, the other end of switch S1 is electrically connected to ground voltage, one end of switch S2 is electrically connected to reference voltage controller 115, and the other end of switch S2 is electrically connected to node voltage V _SW . The switches S1 and S2 are controlled by a control signal and a reverse control signal, respectively. Further, when the termination-on signal is a logic high level, the switch S2 is turned on (ie, turned on), and when the termination-off signal is a logic high level At this time, the switch S1 is turned on.

Next, please refer to FIG. 2, which is a schematic diagram of a reference voltage controller of the controller during a constant on period according to an embodiment of the present invention. One implementation of the reference voltage controller 115 of the controller 11 during the constant on period is shown in FIG. 2, but the implementation of the reference voltage controller 115 described below is not intended to limit the present invention, and the reference voltage controller 115 may also have other Types of implementation.

In the embodiment of FIG. 2, the reference voltage controller 115 includes an error amplifier 1151, a resistor R1, R2, a capacitor C1, an adder AAD1, a transduction amplifier 1152, and a ramp signal generating gas 1153. The error amplifier 1151 is electrically connected to the voltage divider 111, one end of the resistor R1, and the input end of the transconductance amplifier 1152. The output terminal of the transconductance amplifier 1152 is electrically connected to the input terminal of the adder ADD1, and the output terminal of the ramp signal generator is electrically connected to the other input terminal of the adder ADD1. One terminal of the resistor R2 is electrically connected to the positive input terminal of the comparator 114 and the output terminal of the adder ADD1, and the other terminal of the resistor R2 is electrically connected to one terminal of the switch S1 and one terminal of the switch S2. The two ends of the capacitor C1 are respectively electrically connected to the other end of the resistor R1 and the ground voltage.

The negative input terminal and the positive input terminal of the error amplifier 1151 respectively receive the feedback voltage V _FB and the predetermined voltage V _REF (for example, 0.6 volts, but not limited thereto), and generate the feedback voltage V _FB and the predetermined voltage V accordingly. _REF error-amplified signal. The capacitor C1 and the resistor R1 form an RC compensation circuit. The effect of the RC compensation circuit is to stabilize the circuit and reduce the phenomenon of high frequency oscillation. The error amplified signal after passing through the RC compensation circuit is converted into a current signal by the transconductance amplifier 1152. The adder ADD1 superimposes the ramp signal RAMP_SIG to the current signal, and the resistor R2 is used for current sensing to generate a reference voltage V _REFX according to the current signal of the superposed ramp signal RAMP_SIG.

Please note that the ramp signal generator 1153 and the adder ADD1 are added to the reference voltage controller 115 in order to solve the technical problem of signal jitter. Therefore, if there is no severe signal jitter, the ramp signal generator 1153 and the adder ADD1 can be removed from the reference voltage controller 115.

Please refer to FIG. 1 to FIG. 3 at the same time. FIG. 3 is a waveform diagram of the node voltage, the node current, the reference voltage, and the feedback voltage in the step-down converter using the controller in the constant on period of FIG. 2. In this embodiment, at the time point T0, the electronic switching device of the buck regulator 10 is turned on, and the turn-on period P01 is terminated at the time point T1, that is, during the turn-on period P01, the buck regulator 10 is turned on. During the turn-on period P01, the input voltage V _IN generates the relevant output voltage V _OUT and the node voltage V _SW . Due to the charging of the storage inductor L _X , the node voltage V _SW gradually decreases and the node current I _SW gradually increases. During the turn-on period P01, the reference voltage provided by the switching device 116 is a ground voltage, the reference voltage V _REFX is approximately equal to the predetermined voltage V _REF , and the feedback voltage V _FB rises corresponding to the rise of the output voltage V _OUT .

At the time point T1, the end-on signal is generated. Therefore, the electronic switching device of the buck regulator 10 is turned off, the node voltage V _SW of the electronic switching device of the buck regulator 10 is momentarily pulled down, and the energy storage inductor L _X Discharge to the output of the buck regulator 10 is started to generate an output voltage V _OUT . During the off period P12, because the energy storage inductor L _X continues to discharge to the output terminal, the node current I _SW will gradually decrease, the pulled down node voltage V _SW will gradually increase, and the feedback voltage V _FB corresponds to the output voltage V _OUT When the feedback voltage V _{FB is} lower than the reference voltage V _REFX (that is, at the time point T2), a termination shutdown signal for the termination shutdown period P12 is generated. At time T1, the reference voltage provided by the switching device 116 is changed to the node voltage V _SW . Therefore, the reference voltage V _REFX will be immediately pulled down to the node voltage V _SW , and then the reference voltage V _REFX will be turned off during the off period P12. Will gradually rise to the predetermined voltage V _REF . Since the controller 10 in the embodiment of the present invention uses the switching voltage switching device 116 to change the reference voltage provided to pull down the reference voltage V _REFX instantaneously, in addition to improving the noise margin, it has the advantage of fast response .

Next, please refer to FIG. 4, which is a schematic diagram of a buck converter according to another embodiment of the present invention. Compared with the embodiment of FIG. 1, the controller 11 ′ of the step-down converter 1 ′ of FIG. 4 additionally has two switches S3 and S4. One end of the switch S3 is electrically connected to the feedback voltage V _FB , the other end of the switch S3 is electrically connected to the ground, one end of the switch S4 is electrically connected to the reference voltage V _REFX , and the other end of the switch S4 is electrically connected to the comparator through an RC filter circuit. Positive input of 114. The RC filter circuit includes a resistor R _F and a capacitor C _F , one end of the resistor R _F is connected to the switch S4, the other end of the resistor R _F is connected to the positive input terminal of the comparator 114, one end of the capacitor C _F is connected to ground, and the capacitor C The other end of _F is connected to the positive input terminal of the comparator 114. The switches S3 and S4 are controlled by the reverse control signal QB. Therefore, the switches S3 and S4 are turned on only during the off period, so that the comparator 114 compares the reference voltage V _REFX and the feedback voltage V _FB only during the off period.

Please refer to FIG. 4 and FIG. 5 at the same time. FIG. 5 is a waveform diagram of the node voltage, the node current, the voltage on the positive input terminal of the comparator, and the feedback voltage in the step-down converter using the controller of FIG. . The switches S3 and S4 are turned on only during the off period P12, so that the comparator 114 compares the reference voltage V _REFX with the feedback voltage V _FB . Therefore, during the on period P01, the voltage V ′ on the positive input terminal of the comparator 114 _REFX is a lower voltage below the predetermined voltage V _REF . During the off period P12, the switches S3 and S4 are turned on, and the voltage V ′ _REFX on the positive input terminal of the comparator 114 is affected by the reference voltage V _REFX and gradually rises from a lower voltage to a predetermined voltage V _REF . In this way, by adding switches S3 and S4 to the positive input terminal and the negative input terminal of the comparator 114, the difference between the feedback voltage V _FB and the voltage V ′ _REFX can be further opened, and thus more To increase noise margin.

In summary, the controller and the step-down converter used in the constant-on period provided by the embodiment of the present invention have a higher noise margin, so it can solve when the ripple of the output voltage of the step-down regulator is relatively small. The technical problem that the controller is easy to be affected by noise during the constant opening period, which reduces its stability. Preferably, in one of the embodiments, changing the slope of the reference voltage through the ramp signal during the off period can further improve the technical problem of signal jitter. In addition, since the controller uses a switching device to switch the reference voltage corresponding to the reference voltage during the constant on period, it has the advantage of faster response speed.

The above description is only an embodiment of the present invention, and is not intended to limit the patent scope of the present invention.

Claims (8)

A constant on-period controller is used to control a closed period and an on period of a buck regulator, including: a comparator for comparing a feedback voltage generated based on an output voltage of one of the buck regulators with A reference voltage to generate a termination off signal for terminating the off period; an on timer to determine the on period based on an input voltage and an output voltage of the buck regulator, and generate a termination period based on the A termination start signal during the turn-on period; a reference voltage controller electrically connected to the comparator to generate the reference voltage according to the feedback voltage and a predetermined voltage; and a switching device electrically connected to the reference voltage controller, At the beginning of the off period, the reference voltage is momentarily pulled down to a node voltage of an electronic switching device of the buck regulator; wherein the switching device provides a ground voltage as a reference voltage of the reference voltage during the on period, And providing the node voltage as a reference voltage of the reference voltage during the off period. According to the constant opening period controller of the first item of the request, the switch switching device includes: a first switch and a second switch, wherein a first end of the first switch and a first end of the second switch The reference voltage controller is electrically connected, a second end of the first switch and a second end of the second switch are respectively electrically connected to the ground voltage and the node voltage, and the first switch and the second switch are electrically connected. Turned on in response to the termination-off signal and the termination-on signal, respectively. According to the constant opening period controller of the first item of the claim, the reference voltage controller includes: an error amplifier for outputting an error amplification signal according to the feedback voltage and the predetermined voltage; an RC compensation circuit, electrically connected An output terminal of the error amplifier; a transconductance amplifier electrically connected to the output terminal of the error amplifier for converting the error amplified signal after passing the RC compensation circuit into a current signal; and a current sensing The resistor is electrically connected between the output terminal of the error amplifier and the switching device, and is used to convert the current signal into the reference voltage. The constant on period controller according to item 3 of the claim, wherein the reference voltage controller further includes: a ramp signal generator for generating a ramp signal; and an adder electrically connected to the transconductance amplifier The output terminal, an output terminal of the ramp signal generator and the comparator are used to superimpose the ramp signal to the current signal. According to the constant opening period of the first item of the controller, the controller further includes: an RC filter circuit; a first switch and a second switch, wherein a first end of the first switch and a first of the second switch Terminal is electrically connected to the reference voltage controller, a second terminal of the first switch and a second terminal of the second switch are respectively electrically connected to the ground voltage and the RC filter circuit, and the RC filter circuit is electrically connected to the A positive input terminal of the comparator, the first switch and the second switch are controlled by the termination enable signal, so that the comparator performs comparison only during the off period. According to the constant on-time controller of the first item of the request, the controller further includes: an RS flip-flop, electrically connected to the comparator, the on-timer and the step-down regulator, for receiving the termination-off signal and the termination Turn on the signal to generate a control signal and a reverse control signal. According to the constant opening period controller of the first item of the request, the controller further includes: a voltage divider, which is electrically connected to the reference voltage controller, the comparator and the buck regulator to generate the feedback according to the output voltage. Voltage. A step-down converter includes the constant on-period controller according to any one of claims 1 to 7 and the step-down regulator.