JP2008206376A - Switching regulator, and circuit and method for controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a delay occurs until an output voltage becomes stable when returning to a normal load from a light load. <P>SOLUTION: A switching circuit 12 includes a switching transistor M1 and a synchronous rectifying transistor M2 connected in series between an input terminal 102 and ground, and a voltage at a connection point between two transistors is applied to one end of an inductor L1 as a switching voltage Vsw. In a pulse modulator 20, a PWM signal Spwm is generated of which duty ratio is adjusted so that the output voltage (Vout 2) of a step-down type switching regulator 200 approximates a predetermined reference voltage Vref. In a return pulse signal generating part 30, a return pulse signal S1 is generated of which the duty ratio is set without correlating with the output voltage of the step-down type switching regulator 200. In a driver circuit 10, a switching circuit 12 is driven by selecting either one of the PWM signal Spwm or the return pulse signal S1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching regulator, and more particularly to a control technology for a synchronous rectification switching regulator.

  In recent years, electronic devices such as mobile phones, PDAs (Personal Digital Assistants), and personal computers are equipped with lithium ion batteries or the like as a power source. The voltage of the lithium ion battery is about 3V to 4V. If this voltage is supplied to the microcomputer as it is, wasteful power consumption occurs. Therefore, the battery voltage is lowered using a step-down switching regulator, and the constant voltage Generally, it is supplied to microcomputers.

  There are two types of step-down switching regulators: a method using a rectifying diode (hereinafter referred to as a diode rectifying method) and a method using a rectifying transistor instead of a diode (hereinafter referred to as a synchronous rectifying method). In the former case, there is an advantage that high efficiency can be obtained when the load current flowing through the load is low. However, since a diode is required in addition to the inductor and the capacitor outside the control circuit, the circuit area becomes large. In the latter case, the efficiency when the current supplied to the load is small is inferior to the former, but since a transistor is used instead of a diode, it can be integrated inside the LSI, and the circuit area including peripheral components As a result, downsizing is possible. When electronic devices such as mobile phones are required to be downsized, a switching regulator using a rectifying transistor (hereinafter referred to as a synchronous rectification switching regulator) is often used.

In order to improve the efficiency at the time of light load of the switching regulator of the synchronous rectification system, when a light load is detected, unnecessary circuit blocks inside the control circuit of the switching regulator may be stopped to reduce power consumption.
JP 2007-028732 A

The present applicant has come to recognize the following problems when verifying the operation of the switching regulator in a light load state.
The switching regulator generates an error voltage by amplifying an error between the detection voltage corresponding to the output voltage and the reference voltage by an error amplifier. The on / off duty ratio of the switching transistor is set based on the error voltage. As a result, the reference voltage and the detection voltage coincide with each other by feedback, and a desired output voltage is generated.

  Here, when the error amplifier is stopped at the time of light load, the error voltage becomes a voltage level unrelated to the feedback. Thereafter, when returning to the normal load state, a certain amount of time is required until the error voltage returns to a value depending on feedback. Therefore, when returning from a light load to a normal load, a delay may occur until the output voltage is stabilized to a desired voltage value.

  The present invention has been made in view of such problems, and a comprehensive object thereof is to shorten the return time from a light load state to a normal load state in a synchronous rectification switching regulator.

  One embodiment of the present invention relates to a control circuit for a switching regulator. This control circuit includes a switching transistor and a synchronous rectification transistor connected in series between the input terminal and the ground, and one end of an inductor connected to the outside of the control circuit using the voltage at the connection point of the two transistors as a switching voltage. The duty ratio is set without any correlation between the switching circuit applied to the pulse generator, the pulse modulator that generates the pulse modulation signal whose duty ratio is adjusted so that the output voltage of the switching regulator approaches a predetermined reference voltage, and the output voltage of the switching regulator. A return pulse signal generator for generating a return pulse signal to be generated, a driver circuit that selects either the pulse modulation signal or the return pulse signal to switch the switching transistor and the synchronous rectification transistor, and a load driven by the switching regulator When detecting a light load state, at least a part of the control circuit is suspended, and when a return from the light load state to the normal load state is detected, a control unit that operates a part of the suspended control circuit; Prepare. The driver circuit selects the pulse modulation signal in the normal load state, and selects the return pulse signal in the transition period from the light load state to the normal load state.

“No correlation with the output voltage of the switching regulator” means that the duty ratio does not depend on the value of the output voltage. From another point of view, this can also be understood as being generated without feedback.
When a part of the control circuit is stopped in a light load state, it takes a long time for the duty ratio of the pulse modulation signal to approach an ideal value at the time of recovery. According to this aspect, the output voltage can be brought close to a desired value in a short time by restarting switching using the return pulse signal generated regardless of the feedback during the return operation.

  The return pulse signal generation unit may set the duty ratio of the return pulse signal to a predetermined value. In this case, the configuration can be simplified.

The return pulse signal generation unit may set the duty ratio of the return pulse signal according to the ratio between the input voltage applied to the input terminal and the target value of the output voltage defined by the reference voltage.
In this case, since the switching operation is resumed with the duty ratio necessary for optimizing the output voltage, the output voltage can be brought close to the target value in a short time.

  Another aspect of the present invention is a step-down switching regulator. This step-down switching regulator includes a capacitor having one end grounded, an inductor having one end connected to the other end of the capacitor, and any one of the control circuits described above that supplies a switching voltage to the other end of the inductor. The voltage at the other end of the capacitor is output.

  Yet another embodiment of the present invention relates to a method for controlling a switching regulator. In this control method, a step of generating a pulse modulation signal whose duty ratio is controlled so that the output voltage of the switching regulator approaches a predetermined reference voltage, and a return pulse whose duty ratio is set without correlation with the output voltage of the switching regulator When the signal generating step and the light load state of the load driven by the switching regulator are detected, at least a part of the control circuit of the switching regulator is suspended, and the return from the light load state to the normal load state is detected. The step of operating a part of the control circuit that has been suspended, and the pulse modulation signal is selected in the normal load state, the return pulse signal is selected in the transition period from the light load state to the normal load state, and the selected signal is Based on the switching transistor switching transistor And and a step of switching the synchronous rectification transistor.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  The switching regulator according to the present invention can be recovered from a light load state in a short time.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A and the member B are connected” means that the member A and the member B are physically directly connected, or the member A and the member B are in an electrically connected state. Including the case of being indirectly connected through other members that do not affect the above.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical connection. The case where it is indirectly connected through another member that does not affect the state is also included.

  The step-down switching regulator according to the present embodiment is suitably used for driving a stable voltage with respect to a load whose current consumption changes according to an operating state, such as a microcomputer operating at 1.5 V. It is done. Hereinafter, the configuration of the step-down switching regulator according to the present embodiment will be described in detail.

FIG. 1 is a circuit diagram showing a configuration of a step-down switching regulator 200 according to an embodiment. The step-down switching regulator 200 is a synchronous rectification step-down switching regulator, and includes a control circuit 100, an inductor L1, and an output capacitor C1. The control circuit 100 is an LSI (Large Scale Integration) chip integrated on a single semiconductor substrate, and a switching transistor M1 and a synchronous rectification transistor M2 functioning as switching elements are built in the control circuit 100.
One end of the output capacitor C1 is grounded, and the other end is connected to one end of the inductor L1. The other end of the inductor L1 is connected to the control circuit 100, and a switching voltage Vsw is applied.

  The step-down switching regulator 200 controls the current flowing through the inductor L1 by the control circuit 100, steps down the battery voltage Vbat by charging the output capacitor C1, and supplies the voltage appearing at the output capacitor C1 to a load circuit (not shown). ).

  The control circuit 100 includes an input terminal 102, a switching terminal 104, an output terminal 106, and a ground terminal 108 as input / output terminals. An input voltage Vin is applied to the input terminal 102. The switching terminal 104 is connected to the inductor L1 and outputs a switching voltage Vsw generated inside the control circuit 100. The output terminal 106 is a terminal to which the output voltage Vout applied to the load circuit is fed back. The ground terminal 108 is grounded.

  The control circuit 100 includes a driver circuit 10, a pulse modulator 20, a return pulse signal generation unit 30, a selector SW1, a control unit 40, a light load detection unit 42, a normal load detection unit 44, resistors R1 and R2, and a switching circuit 12. .

The switching circuit 12 includes a switching transistor M1 and a synchronous rectification transistor M2. The switching transistor M1 is a P-channel MOS transistor, and has a source terminal connected to the input terminal 102 and a drain terminal connected to the switching terminal 104. The back gate terminal of the switching transistor M1 is connected to the input terminal 102.
The synchronous rectification transistor M2 is an N-channel MOS transistor, the source terminal is grounded, and the drain terminal is connected to the drain terminal of the switching transistor M1 and the switching terminal 104. The back gate terminal of the synchronous rectification transistor M2 is grounded.

  The switching transistor M1 and the synchronous rectification transistor M2 are connected in series between the input terminal 102 to which the input voltage Vin is applied and the ground, and the voltage at the connection point of the two transistors is used as one switching voltage Vsw at one end of the inductor L1. Apply.

  The pulse modulator 20 generates a pulse modulation signal Spwm. The duty ratio of the pulse modulation signal Spwm is adjusted by the pulse width modulation (PWM) method so that the output voltage Vout of the step-down switching regulator 200 approaches a predetermined target voltage.

In order to realize this function, the pulse modulator 20 includes an error amplifier 22, a PWM comparator 24, an oscillator 26, an RS flip-flop 28, a capacitor C10, and a resistor R10.
The resistors R1 and R2 divide the output voltage Vout and output a detection voltage Vout2 multiplied by R2 / (R1 + R2) to the inverting input terminal of the error amplifier 22. The reference voltage Vref is input to the non-inverting input terminal of the error amplifier 22. The error amplifier 22 is a gm amplifier, and amplifies an error between the detection voltage Vout2 and the reference voltage Vref and outputs it as an error voltage Verr.

  The capacitor C10 and the resistor R10 are connected in series between the output terminal of the error amplifier 22 and the ground terminal to form a low-pass filter. The error voltage Verr is smoothed by a low-pass filter. The oscillator 26 oscillates at a predetermined frequency and outputs a periodic voltage Vosc having a triangular wave shape or a sawtooth wave shape. The PWM comparator 24 compares the periodic voltage Vosc and the error voltage Verr, and outputs a pulse signal Vr that is at a high level when Vosc> Verr and at a low level when Vosc <Verr. The oscillator 26 outputs a set signal Vs having a predetermined level for each cycle of the periodic voltage Vosc.

  The pulse signal Vr is input to the reset terminal of the RS flip-flop 28, and the set signal Vs is input to the set terminal. The output signal Spwm of the RS flip-flop 28 is a signal that is pulse-width modulated in accordance with the output voltage Vout and the reference voltage Vref.

  The configuration of the pulse modulator 20 is not limited to that of FIG. 1, and the configuration may be such that the output of the PWM comparator 24 is directly output as a pulse width modulation signal without using the RS flip-flop 28. An operational amplifier may be used as the error amplifier 22 instead of the gm amplifier. Further, the duty ratio may be adjusted by a pulse frequency modulation method (PFM) or a fixed on-time method without being limited to the PWM method.

  The return pulse signal generation unit 30 generates a return pulse signal S1 in which the duty ratio is set without correlation with the output voltage Vout of the step-down switching regulator 200. The duty ratio is set to a predetermined value, for example, 30%.

  The selector SW1 receives the PWM signal Spwm or the return pulse signal S1. The selector SW1 selects either the PWM signal Spwm or the return pulse signal S1 in accordance with an instruction from the control unit 40 described later, and outputs the selected signal to the driver circuit 10.

  The driver circuit 10 complementarily turns on and off the switching transistor M1 and the synchronous rectification transistor M2 based on either the PWM signal Spwm or the return pulse signal S1 output from the selector SW1.

  The light load detector 42 detects the light load state of the load driven by the step-down switching regulator 200. Detection of a light load state is not particularly limited, and can be realized by various known methods. For example, the light load state may be detected by monitoring the voltage across the synchronous rectification transistor M2, or the light load state may be detected by monitoring the error voltage Verr output from the error amplifier 22. The normal load state means a state that is not a light load state.

  The normal load detection unit 44 detects that the light load state has changed to the normal load state. In the present embodiment, the detection voltage Vout2 is compared with a predetermined threshold voltage Vth2, and when Vout2 <Vth2, the transition from the light load state to the normal load state is detected. It may be detected by other methods.

When the light load state is detected by the light load detector 42, the controller 40 pauses at least a part of the control circuit 100 in order to reduce power consumption. The setting of the dormant state is specified by the enable signal Sen. For example, the control unit 40 may pause the error amplifier 22, the PWM comparator 24, and the oscillator 26 in a light load state.
Further, when the normal load detection unit 44 detects the return from the light load state to the normal load state, the control unit 40 returns a part of the control circuit 100 that has been stopped from the stop to perform a normal operation.

  Furthermore, the control unit 40 controls the state of the selector SW1. Specifically, the control unit 40 turns on the selector SW1 on the PWM signal Spwm side in the normal load state, and turns on the selector SW1 on the return pulse signal S1 side in the transition period from the light load state to the normal load state. .

  The driver circuit 10 determines the gate voltages Vg1 and Vg2 of the switching transistor M1 and the synchronous rectification transistor M2 based on either the PWM signal Spwm output from the pulse modulator 20 or the return pulse signal S1 (hereinafter referred to as pulse signal S2). To control. The switching transistor M1 is turned on when the gate voltage Vg1 is at a low level and turned off when the gate voltage Vg1 is at a high level. The synchronous rectification transistor M2 is turned on when the gate voltage Vg2 is at a high level and turned off when the gate voltage Vg2 is at a low level.

  The driver circuit 10 sets the ratio of the time during which the switching transistor M1 and the synchronous rectification transistor M2 are turned on based on the high level and low level duty ratio of the pulse signal S2, and turns the two transistors on and off in a complementary manner. Let In order to prevent the switching transistor M1 and the synchronous rectification transistor M2 from being turned on at the same time and causing a through current to flow, the driver circuit 10 has a period (dead time) during which the gate voltage Vg1 is at a high level and the gate voltage Vg2 is at a low level Provided every period.

  As a result, the driver circuit 10 drives the switching circuit 12 based on the pulse modulation signal Spwm in the normal load state, and the switching circuit 12 based on the return pulse signal S1 in the transition period from the light load state to the normal load state. Drive.

The above is the overall configuration of the control circuit 100 and the step-down switching regulator 200. Next, the operation of the step-down switching regulator 200 will be described.
2A to 2G are time charts showing the operation of the step-down switching regulator 200 of FIG. 6A shows the periodic voltage Vosc and the error voltage Verr, FIG. 4B shows the PWM signal Spwm, and FIG. 4C shows the detection voltage Vout2 when the switching circuit 12 is driven only by the PWM signal Spwm. (D) shows the return pulse signal S1, FIG. (E) shows the state of the selector SW1, (f) shows the pulse signal S2, and (g) shows the switching circuit 12 by the pulse signal S2. The detection voltage Vout2 when driven is shown.

  A normal load state is present before time t0. When the light load state is reached at time t0, the current flowing from the output capacitor C1 to the load decreases, and the output voltage Vout (detection voltage Vout2) increases. When the transition to the light load state is detected by the light load detector 42, the duty ratio of the PWM signal Spwm gradually decreases, and eventually the switching of the switching transistor M1 and the synchronous rectification transistor M2 is stopped. In the light load state, the operations of the error amplifier 22, the PWM comparator 24, the oscillator 26, and the like are also stopped. When the error amplifier 22 stops, the error voltage Verr decreases.

  When the switching of the switching transistor M1 and the synchronous rectification transistor M2 is stopped, the supply of charge to the output capacitor C1 is stopped, so that the detection voltage Vout2 gradually decreases.

  At time t1, the light load state returns to the normal load state. As a result, since a current flows from the output capacitor C1 to the load, the detection voltage Vout2 decreases. When the detection voltage Vout2 decreases to the threshold voltage Vth2, the normal load detection unit 44 detects the return to the normal load state, and the operations of the error amplifier 22, the PWM comparator 24, and the oscillator 26 are resumed. As a result, the error voltage Verr gradually increases with time. Here, since the error voltage Verr rises gently due to the influence of the capacitor C10 and the resistor R10, the duty ratio of the PWM signal Spwm gradually changes to the original duty ratio.

  In order to clarify the effect of the step-down switching regulator 200 according to the present embodiment, the operation when the return pulse signal generation unit 30 and the selector SW1 are not used will be described with reference to FIG. In this case, if the duty ratio of the PWM signal Spwm increases gently, the rise of the detection voltage Vout2 also becomes gentle, and the time τ1 until it coincides with the reference voltage Vref becomes long. This is a problem to be solved by the step-down switching regulator 200 according to the present embodiment.

  The step-down switching regulator 200 according to the present embodiment solves this problem as follows.

  The return pulse signal generation unit 30 generates a return pulse signal S1 whose duty ratio is determined regardless of feedback. During a predetermined period τ3 from time t2, the selector SW1 is turned on to the return pulse signal S1. The predetermined period τ3 may be determined according to the time required for the error voltage Verr to return to a somewhat large value after the operation of the error amplifier 22 is started.

That is, the switching transistor M1 and the synchronous rectification transistor M2 are turned on and off by the return pulse signal S1 having a duty ratio larger than that of the PWM signal Spwm. As a result, as shown in FIG. 5G, the detection voltage Vout2 rises more quickly than in the case shown in FIG. Thereafter, at time t3, the selector SW1 is turned on to the PWM signal Spwn side. After time t3, the output voltage Vout is adjusted by feedback so that the detection voltage Vout2 approaches the reference voltage Vref.
According to the step-down switching regulator 200 according to the present embodiment, the time τ2 until it coincides with the reference voltage Vref can be shortened compared to the time τ1 in FIG.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

In the embodiment, the case where the pulse width of the return pulse signal S1 is fixed to a predetermined value has been described, but the present invention is not limited to this. For example, the return pulse signal generation unit 30 may set the duty ratio of the return pulse signal S1 according to the ratio of the input voltage Vin and the target value (= Vref × (R1 + R2) / R2) of the output voltage Vout. . In the steady state of the normal load state, the following relationship is established between the target value of the output voltage Vout and the input voltage Vin.
Vout = Vin × Dx
Here, Dx is the ratio of the ON time of the switching transistor M1 and the synchronous rectification transistor M2, that is, the duty ratio of the PWM signal Spwm.

  Therefore, by setting the duty ratio of the return pulse signal S1 according to the target values of the input voltage Vin and the output voltage Vout, it is possible to return to normal operation in a shorter time.

  In the embodiment, a step-down switching regulator is described, but the present invention can also be applied to a step-up switching regulator.

  In the embodiment, the case where the control circuit 100 is integrated in one LSI has been described. However, the present invention is not limited to this, and some components are provided as discrete elements or chip components outside the LSI. Or you may comprise by several LSI.

  Further, in the present embodiment, the setting of high level and low level logical values is merely an example, and can be freely changed by appropriately inverting it with an inverter or the like.

1 is a circuit diagram showing a configuration of a step-down switching regulator according to an embodiment. 2A to 2G are time charts showing the operation of the step-down switching regulator of FIG.

Explanation of symbols

  100 control circuit, 102 input terminal, 104 switching terminal, 106 output terminal, 108 ground terminal, 200 step-down switching regulator, 10 driver circuit, 12 switching circuit, 20 pulse modulator, 22 error amplifier, 24 PWM comparator, 26 oscillator, 28 RS flip-flop, 30 return pulse signal generation unit, 40 control unit, 42 light load detection unit, 44 normal load detection unit, SW1 selector, C1 output capacitor, L1 inductor, M1 switching transistor, M2 synchronous rectification transistor, S1 return pulse signal.

Claims (5)

A control circuit for a switching regulator,
A switching circuit including a switching transistor and a synchronous rectification transistor connected in series between an input terminal and the ground, and applying a voltage at a connection point between the two transistors as one switching voltage to one end of an inductor connected to the outside of the control circuit When,
A pulse modulator that generates a pulse modulation signal in which a duty ratio is adjusted so that an output voltage of the switching regulator approaches a predetermined reference voltage;
A return pulse signal generator for generating a return pulse signal in which a duty ratio is set without correlation with the output voltage of the switching regulator;
A driver circuit that selects either the pulse modulation signal or the return pulse signal to switch the switching transistor and the synchronous rectification transistor;
When the light load state of the load driven by the switching regulator is detected, at least a part of the control circuit is suspended, and when the return from the light load state to the normal load state is detected, one of the suspended control circuits is detected. A control unit for operating the unit,
With
The control circuit, wherein the driver circuit selects the pulse modulation signal in a normal load state and selects the return pulse signal in a transition period from a light load state to a normal load state.   The control circuit according to claim 1, wherein the return pulse signal generation unit sets a duty ratio of the return pulse signal to a predetermined value. The return pulse signal generator is
2. The duty ratio of the return pulse signal is set according to a ratio between an input voltage applied to the input terminal and a target value of the output voltage defined by the reference voltage. Control circuit. A capacitor with one end grounded;
An inductor having one end connected to the other end of the capacitor;
The control circuit according to any one of claims 1 to 3, wherein the switching voltage is supplied to the other end of the inductor;
And a voltage at the other end of the capacitor is output. A switching regulator control method comprising:
Generating a pulse modulation signal whose duty ratio is controlled so that the output voltage of the switching regulator approaches a predetermined reference voltage;
Generating a return pulse signal in which the duty ratio is set without correlation with the output voltage of the switching regulator;
When a light load state of a load driven by the switching regulator is detected, at least a part of the control circuit of the switching regulator is suspended, and when a return from the light load state to the normal load state is detected, the suspended control is performed. Operating a portion of the circuit;
The pulse modulation signal is selected in a normal load state, and the return pulse signal is selected in a transition period from a light load state to a normal load state. Based on the selected signal, the switching transistor and the synchronous rectification transistor of the switching regulator Switching between
A control method comprising:

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