KR101642761B1 - Soft start apparatus and method for dc-dc converter - Google Patents

Abstract

Disclosed are a soft start apparatus and a soft start method for a DC-DC converter. The soft start apparatus for a DC-DC converter supplies a current in a linear mode to linearly increase an output voltage of a DC-DC converter, performs a switching operation according to a PWM duty in a switching mode to increase the output voltage to a target level, determines whether to enter the switching mode in the linear mode, and controls the PWM duty based on a control signal in the switching mode. Also, a corresponding apparatus generates a control signal having an initial slope in a mode-switching section to respond to the slope in an early stage of the switching mode to induce the PWM duty to gradually increase, and controls the PWM duty based on a current limit value during the switching mode. Accordingly, a momentary inrush current generated when switching to the switching mode after the linear mode can be effectively prevented, and a mode can be stably switched.

Description

Technical Field [0001] The present invention relates to a soft start device and a method for a DC-DC converter,

The present invention relates to a soft-start device and method for a DC-DC converter, and more particularly to a soft-start device and method for a DC-DC converter capable of effectively suppressing an instantaneous inrush current generated when switching to a switching mode after a linear mode .

An excessive inrush current may occur at the time of initial startup of the DC-DC converter performing the boost operation. Therefore, it is necessary to apply the soft start technique to prevent the inrush current.

Conventional soft start techniques include a linear charge method in which the output voltage of a DC-DC converter is increased by using a capacitor charging / discharging, a switching method in which the output voltage of the DC-DC converter is raised by changing the PWM duty in the soft- switching method.

In recent years, a soft start technique has been proposed in which the above-described linear charge method and switching method are combined to switch to a switching mode after the linear mode.

However, in this case, the current flowing in the inductor of the DC-DC converter rapidly increases (for example, within 2 to 3 cycle clocks) during the period in which the mode conversion from the linear mode to the switching mode takes place, resulting in an excessive inrush current.

Such instantaneous inrush current generation causes deterioration of the inductor, circuit damage, and excessive response of the output voltage.

Korean Patent Registration No. 10-1477626, Published on Dec. 30, 2014.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the problems of the conventional art as described above, and it is an object of the present invention to provide a DC-DC converter which can prevent instantaneous inrush current that occurs when switching to a switching mode after a linear mode, DC converter and a method thereof.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. There will be.

According to an aspect of the present invention, there is provided a soft start device for a DC-DC converter, the method comprising: determining whether to enter a switching mode from a linear mode; controlling the PWM duty based on a control signal in a switching mode; a mode switching controller for generating a control signal having a slope to induce the PWM duty to be gradually increased in response to the slope at the beginning of the switching mode; And an overcurrent prevention unit for limiting the current of the DC-DC converter by controlling the PWM duty based on a current limit value during a switching mode, wherein the linear charger maintains the mode switching control unit in a reset state during a linear mode, When the mode is terminated, the reset of the mode switching control unit is released to form the slope.

In the soft start device for a DC-DC converter according to the present invention, the mode switching control section controls the PWM duty to a lowest duty during a linear mode, and the PWM duty corresponding to the slope at the beginning of the switching mode, To be gradually increased.

In the soft start device for a DC-DC converter according to the present invention, the mode switching control section generates an error signal for switching to a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the DC-DC converter An error amplifier; A ramp controller for generating a control signal having an initial slope in response to an error signal output from the error amplifier; And a comparator for controlling the PWM duty based on the sum signal of the current sense signal and the ramp signal of the DC-DC converter in the switching mode and a control signal having an initial slope output from the ramp controller.

The soft-start device for a DC-DC converter according to claim 3, wherein the lamp controller is connected between an output terminal and a ground terminal of the error amplifier to linearly increase an internal resistance value at the beginning of a switching mode, And a variable resistance portion that forms an initial slope in the control signal.

In the soft-start device for a DC-DC converter according to the present invention, the linear charger maintains the lamp controller in a reset state during a linear mode, and when the linear mode ends, Reset can be disabled.

The soft start device for a DC-DC converter according to the present invention may further include a soft start timer for determining a soft start time by setting a current limit value of the overcurrent prevention portion, wherein the overcurrent prevention portion includes a current sense When the signal reaches the current limit value, the PWM duty can be controlled by generating a current limit signal.

Meanwhile, a soft start method for a DC-DC converter according to the present invention includes: linearly increasing an output voltage of a DC-DC converter from an initial level by supplying a current in a linear mode; Determining whether to enter the switching mode in the linear mode based on the change in the output voltage; Generating a control signal having an initial slope upon entering the switching mode; Controlling the PWM duty to be gradually increased in response to the slope at the beginning of the switching mode; Controlling the PWM duty based on a control signal stabilized at one voltage level past the slope after the beginning of the switching mode to raise the output voltage to a target level; And limiting the current of the DC-DC converter by controlling the PWM duty based on a current limit value during a switching mode, the method comprising: maintaining a reset state during a linear mode; Release the reset.
A soft start method for a DC-DC converter according to the present invention is characterized by comprising the steps of: generating an error signal for switching to a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the DC- A control signal having an initial slope can be generated in response to the error signal, and the control signal having an initial slope and a sum signal of the current sense signal and the ramp signal of the DC-DC converter at the beginning of the switching mode The PWM duty can be controlled on the basis.
The soft start method for a DC-DC converter according to the present invention may linearly increase an internal resistance value at the beginning of a switching mode so that an initial slope is formed in a control signal output according to the resistance value.

According to the soft start device and method for the DC-DC converter of the present invention, it is possible to effectively prevent instantaneous inrush current that appears when switching to the switching mode after the linear mode, and stable mode switching can be performed.

1 is a configuration diagram of a soft-start device for a DC-DC converter according to an embodiment of the present invention;
2 is an exemplary timing diagram for illustrating operation of a soft-start device for a DC-DC converter according to an embodiment of the present invention;
3 is a reference timing diagram for comparing and illustrating effects of a soft-start device for a DC-DC converter according to an embodiment of the present invention.

Hereinafter, a soft start apparatus and method for a DC-DC converter according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a configuration diagram of a soft start device for a DC-DC converter according to an embodiment of the present invention.

The present embodiment is for implementing a soft-start use with the linear mode and the switching mode, the soft-start period while the output voltage (V _OUT) of the DC-DC converter, but raised up to the target level, the output voltage for the linear region (V _OUT ) Is raised from the initial level by a predetermined level, and then the switching period is switched to raise the output voltage V _OUT back to the target level.

In Fig. 1, the inductor L is connected to an input power source.

The first power transistor N1 and the second power transistor N2 are connected in parallel to the inductor L of the DC-DC converter.

The first and second power transistors N1 and N2 may be implemented as MOS transistors.

The mode switch SW is selectively connected to the linear charger 10 and the PWM driver 20 according to mode switching.

In the linear mode, the mode switch SW is connected to the linear charger 10, and the gate of the first power transistor N1, which charges the output capacitor C, is connected to the linear charger 10. In the switching mode, the mode switch SW is connected to the PWM driver 20 so that the gate of the first power transistor N1 is connected to the PWM driver 20. [

The linear charger 10 operates in a linear mode and supplies current to the output capacitor C of the DC-DC converter to linearly increase the output voltage V _OUT .

In one embodiment, the linear charger 10 described above mirrors the current flowing in the inductor L and charges the output capacitor C by the mirrored current so that the output voltage V _OUT of the DC-DC converter is reduced from the initial level And is caused to rise linearly until the input voltage (V _IN ) level is almost reached.

The PWM driver 20 alternately switches the pair of power transistors N1 and N2 connected in parallel to the inductor L of the DC-DC converter in accordance with the PWM duty in the switching mode to generate the output voltage V _OUT ) From the input voltage (V _IN ) level to the target level.

During the switching period, the PWM duty of the PWM driver 20 is basically controlled by the PWM signal PWM_IN generated in the mode switching control unit 30. [

However, when the current sense signal i_sense corresponding to the current flowing in the inductor L reaches the current limit value Limit_ref, the overcurrent prevention unit 41 outputs the current limit signal I_LIMIT to control the PWM duty The current of the inductor L is limited.

The overcurrent prevention unit 41 has a function of limiting the amount of current that can instantaneously increase with the lowest duty control and controls the PWM duty based on the current limit value Limit_ref during the switching mode to control the inductor L of the DC- To protect the circuit.

The above-mentioned overcurrent prevention unit 41 may be implemented by a comparator. The comparator receives the current sense signal i_sense corresponding to the current flowing in the inductor L of the DC-DC converter and compares it with the current limit value Limit_ref. When the current sense signal i_sense reaches the current limit value Limit_ref The current limit signal I_LIMIT is outputted to the PWM driver 20 to control the PWM duty to the lowest duty.

The soft start timer 42 can set a current limit value (Limit_ref) of the overcurrent prevention unit 41 to determine a desired soft start time by using a current amount controllable.

The mode switching control unit 30 generates the PWM signal PWM_IN based on the control signal E / A OUT to determine whether to switch from the linear mode to the switching mode and increase the output voltage V _OUT in the switching mode Thereby controlling the PWM duty.

At this time, the mode switching control unit 30 is for realizing linear control at the time of mode switching and generates a control signal E / A OUT having an initial slope so that the control signal E / And induces the PWM duty to be gradually increased in response to the slope.

To this end, the mode switching control unit 30 may include an error amplifier 31, a ramp controller 32, and a comparator 35.

The error amplifier 31 compares the feedback voltage V _FB and the reference voltage V _REF at the time of departure from the linear mode and enters the switching mode. The error amplifier 31 outputs the output voltage V DC of the DC- (V _REF , V _FB ) obtained by receiving the feedback voltage V _FB (divided output voltage) obtained from the reference voltage V _OUT and receiving the reference voltage V _REF through the non-inverting Level error signal (E / A OUT ') for switching to the switching mode on the basis of the difference.

When the error amplifier 31 outputs a high level error signal E / A OUT ', the lamp controller 32 generates a control signal E / A OUT having an initial slope in response thereto.

The adder 36 adds the current sense signal i_sense fed back from the DC-DC converter and the ramp signal Ramp outputted from the ramp generator (not shown), and outputs the sum signal through the non-inverting (+) terminal And inputs it to the comparator 35.

A control signal E / A OUT having an initial slope provided through the lamp controller 32 is input to the inverting (-) terminal of the comparator 35.

The comparator 35 compares the sum of the current sensing signal i_sense and the ramp signal Ramp of the DC-DC converter during the switching mode and the control signal E / A OUT having the initial slope output from the ramp controller 32, And compares the two signals and generates a PWM signal PWM_IN according to the comparison result to control the PWM duty.

In one embodiment, the ramp controller 32 provides a forward slope with artificially linearity when the output of the error amplifier 31 transitions from a low level to a high level to produce a control signal E / A OUT having an initial slope, And a variable resistance unit 33 connected between the output terminal of the error amplifier 31 and the ground terminal as shown in FIG.

The variable resistor unit 33 gradually increases the internal resistance value in response to the application of a high level error signal E / A OUT 'from the error amplifier 31 so that the output voltage of the variable resistor unit 33 increases So that the initial slope is given to the control signal (E / A OUT) outputted in accordance with the resistance value of the variable resistor section (33).

The buffer 34 connected to the output terminal of the error amplifier 31 receives the output voltage of the linearly increasing variable resistor 33 and supplies it to the inverting (-) terminal of the comparator 35.

Described linear charger 10 maintains the lamp controller 32 of the mode switching control unit 30 in the reset state during the linear mode and controls the lamp controller 32 to form the initial slope of the control signal Thereby releasing the reset so that the lamp controller 32 can be operated.

For example, when the lamp controller 32 is implemented with the variable resistor 33, the linear charger 10 maintains the variable resistor 33 in the reset state during the linear mode, while the output voltage V _OUT is the input voltage V _IN ) level and terminates the linear mode, the reset of the variable resistance portion 33 is canceled so that the resistance value can be varied.

Accordingly, the internal resistance value of the variable resistor unit 33 gradually increases at the beginning of the switching period in which the linear mode is switched to the switching mode, and the error signal E / A OUT ' The initial slope of the control signal E / A OUT can be formed while the output voltage of the resistor 33 linearly increases.

The linear charger 10 holds the lamp controller 32 of the mode switching control unit 30 in the reset mode in the linear mode and releases the reset at the end of the linear mode to drive the lamp controller 32, (E / A OUT) is gradually changed by the linearity.

If the lamp controller 32 is not driven, a high level output of the error amplifier 31 is directly applied to the comparator 35 when the switching mode is entered, and one voltage level is applied to the control signal E / The PWM duty rapidly changes, resulting in an excessive response.

On the other hand, in the present embodiment, a control signal for controlling the PWM duty corresponding to the output (E / A OUT ') of the error amplifier 31 when the lamp controller 32 is not driven during the linear mode and enters the switching mode E / A OUT). At this time, a slope is given to the control signal E / A OUT by the operation of the lamp controller 32 to slowly change the PWM duty.

The ramp controller 32 does not directly raise the control signal E / A OUT to the high level at the time of entering the switching mode but gradually raises the slope so that the control signal E / A OUT) has a gentle level transition characteristic.

Accordingly, the sudden change in PWM duty at the time of mode switching can instantaneously increase the amount of current instantaneously, thereby preventing an excessive inrush current from occurring.

The PWM driver 20 described above turns on and off the two power transistors N1 and N2 alternately according to the PWM duty set in correspondence with the PWM signal PWM_IN applied from the comparator 35 in the switching mode Performs a switching operation to raise the output voltage (V _OUT ) to a target level.

Meanwhile, the comparator that implements the overcurrent prevention unit 41 detects the current flowing through the inductor L and transmits the current limit signal I_LIMIT to limit the current flowing in the inductor L to a current limit value or less. The degree of error depends on the performance of the comparator.

The use of high-performance comparators results in faster signal comparisons and propagations, which can provide nearly the same results as the design specifications, while increasing the value of the supply current.

In addition, since the comparator with a general structure that can be used for overcurrent prevention is for the protection function, a precise comparison value is not required. Therefore, if the current flowing in the inductor L of the DC-DC converter is limited by using a comparator having a general structure, a current value larger than a desired value is limited by a delay in signal comparison and transmission.

In this embodiment, linear control is performed in the mode switching mode in which the output of the error amplifier 31 is controlled to achieve linear PWM duty control in the period where the mode switching occurs, so that even if the high performance comparator is not used, ) Is prevented from rising sharply, and stable mode switching can be performed.

2 is an exemplary timing diagram for explaining the operation of the soft-start device for a DC-DC converter according to an embodiment of the present invention.

2, the soft start section D2 includes a first section SS1 operating in a linear mode, a second section SS2 being an initial section of the switching mode, a third section SS2 serving as a stabilization section after the start of the switching mode, (SS3).

2 (a) to 2 (b) show the output voltage V _OUT of the DC-DC converter, the output LCM of the linear charger 10, the output SS_T of the soft-start timer 42, ), A control signal (E / A OUT), and a current change (Inductor Current) flowing in the inductor (L) of the DC-DC converter.

The operation of the soft-start device for the DC-DC converter will be described below for each section.

First, in the first section SS1, the output voltage V _OUT rises due to the operation of the linear charger 10.

The linear charger 10 supplies the current of the output capacitor C by current mirroring with the first power transistor N1 for the boost operation to linearly change the output voltage V _OUT of the DC-DC converter from the initial level (Fig. 2 (A)).

When the output voltage V _OUT gradually increases during the linear charge operation, the voltage V _ds of the first power transistor N 1 decreases and the amount of the mirrored current decreases.

In order to prevent this, switching from the linear mode to the switching mode occurs.

The error amplifier 31 determines the switching to the switching mode based on the change of the output voltage V _OUT .

The above-described error amplifier 31 compares the reference voltage V _REF with the feedback voltage V _FB of the DC-DC converter to determine whether to switch from the linear mode to the switching mode, A high level error signal is generated.

The linear charger 10 terminates its operation to start the operation of the lamp controller 32 to switch to the switching mode at a time point when the output voltage V _OUT rises and almost reaches the input voltage V _IN level.

In one embodiment, the linear charger 10 outputs a high level reset signal LCM to the lamp controller 32 during the first section SS1 until the output voltage V _OUT reaches the input voltage V _IN And holds the lamp controller 32 in the reset state (B in Fig. 2). At this time, the reset signal LCM keeps the lamp controller 32 in the reset state and the control signal E / A OUT appears at the low level (Fig. 2E).

And the second section SS2, which is the initial section of the second switching mode.

The second section SS2 is a section for preventing a momentary inrush current that may occur when the linear mode is switched to the switching mode.

The PWM duty is controlled to the lowest duty as the control signal E / A OUT applied to the comparator 35 during the above-described linear mode is at the low level.

When the output voltage V _OUT reaches the input voltage V _IN level due to the operation of the linear charger 10 over time, the output of the linear charger 10 becomes low level (B in FIG. 2). At this time, the reset of the lamp controller 32 in the mode switching control unit 30 is released, and the lamp controller 32 is released from the reset state to start the operation.

As a result, an initial slope is formed in which the signal level linearly increases in the control signal E / A OUT (FIG.
The linear charger 10 maintains the reset state of the lamp controller 32 of the mode switching control unit 30 during the linear mode and releases the reset when the linear mode is ended to operate the lamp controller 32, So that an initial slope of the slope is formed.

When the lamp controller 32 is embodied as the variable resistance portion 33, the resistance value increases linearly from 0 OMEGA as the reset is released. Accordingly, the output voltage of the lamp controller 32 gradually rises, and the operation of the comparator 35 gradually loosens from the minimum duty control to increase the duty smoothly.

In one embodiment, the control signal E / A OUT starts at 0 [V] at the beginning of the second section SS2 and increases linearly during the second section SS2 as the resistance value changes Of the. Then, when the resistance value increases to the unit of M? (Mega Ohm), the lamp controller 32 becomes the high impedance state, and forced duty control by the lamp controller 32 becomes impossible, and the control goes to the third section SS3 .

The ramp controller 32 forms an initial slope of the control signal E / A OUT during the corresponding second section SS2 in the beginning of the switching mode so that the PWM duty is reduced in response to the initial slope of the control signal E / And gradually increases from the lowest duty to the maximum duty.

The linear PWM duty control of the lamp controller 32 prevents the inductor L from abruptly rising in the mode switching period (D1 in FIG. 2).

Third is the third period SS3 which is the stabilization period after the start of the switching mode.

In the third period SS3, the control signal E / A OUT is stabilized to a high level after the initial slope.

The PWM duty is normally controlled by the negative feedback of the error amplifier 31 in the third section SS3 after the initial slope of the control signal E / A OUT.

That is, in the third period SS3, the comparator 35 controls the PWM duty based on the control signal E / A OUT stabilized at the high level after passing through the slope after the start of the switching mode so that the output voltage V _OUT becomes the target level (Fig. 2 (a) and (b)).

In the second section SS2, the linear duty PWM control limits the abrupt duty change to naturally make the current limit. In the third section SS3, the current limiting is performed by the operation of the overcurrent prevention section 41. [

The overcurrent prevention unit 41 operates during the switching mode to limit the current of the DC-DC converter based on the current limit value Limit_ref (FIG.

In the third section SS3, driving is performed in the switching mode. In the soft start section D2, the low current limit value Limit_ref set by the overcurrent prevention section 41 is provided, Can be protected.

That is, the current limit value (Limit_ref) of the soft start section D2 is designed to be smaller than the normal operation section after the soft start section D2 so as to suppress abrupt current supply (FIG.

When a current larger than a desired current limit value Limit_ref flows during the rise of the output voltage V _OUT to the target level by the switching operation, the current limit signal I_LIMIT outputted from the overcurrent prevention unit 41 causes the PWM duty Is controlled.

After the soft start period (D2), the current limit value (Limit_ref) is changed to a larger value so as not to affect the current driving capability in the normal operation period.

The soft-start time can be determined by the output SS_T of the soft-start timer 42 (Fig. 2).

3 is a reference timing diagram for comparing and illustrating effects of the soft-start device for a DC-DC converter according to an embodiment of the present invention.

3A through 3E show the output voltage V _OUT of the DC-DC converter, the output SS_T of the soft-start timer 42, the current limit value Limit_ref when the lamp controller 32 is not driven, The output (E / A OUT ') of the error amplifier 31, and the current change (Inductor Current) flowing in the inductor L of the DC-DC converter.

During the linear mode, the lamp controller 32 is not driven and the output (E / A OUT ') of the error amplifier 31 appears at a low level. The PWM duty is controlled to the lowest duty.

The error amplifier 31 amplifies and outputs the difference between the feedback voltage V _FB and the reference voltage V _REF and the comparator 35 outputs the output E / A OUT 'of the error amplifier 31, The PWM duty is controlled to generate the desired output voltage V _OUT .

At this time, when the high level output (E / A OUT ') of the error amplifier 31 is applied to the comparator 35 in the initial period of entering the switching mode, the result is suddenly switched from the minimum duty control to the maximum duty control, Which rapidly increases the current of the inductor L (Fig. 3, D3).

In this embodiment, the control signal E / A OUT having the initial slope is generated in consideration of this point, and is controlled to be gently switched to the maximum duty control at the lowest duty control based on the linearity of the slope at the beginning of the switching mode.

This linear PWM duty control is performed within a very short time corresponding to the initial period of entering the switching mode and naturally restricts the current flowing in the inductor L of the DC-DC converter at the mode switching time (see FIG. 2, D1). The current of the inductor L is limited by the overcurrent prevention unit 41 in the period after the beginning of the switching mode.

For example, if the soft-start period D1 including the linear period and the switching period is set to several ms, the above-described linear PWM duty control is performed within the 100s section SS2 of the mode switching time.

Accordingly, it is possible to effectively limit the inrush current at the mode switching time without increasing the soft start time.

The configuration of the soft-start device for a DC-DC converter according to the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea of the present invention.

L: Inductor, C: Output capacitor,
N1, N2: power transistor, 10: linear charger,
20: PWM driver, 30: Mode switching control section,
31: error amplifier, 32: lamp controller,
33: variable resistor section, 34: buffer,
35: comparator, 41: overcurrent prevention part,
42: Soft start timer

Claims (9)

A linear charger that supplies current in a linear mode to linearly raise an output voltage of the DC-DC converter from an initial level;
A PWM driver for performing a switching operation according to a PWM duty in a switching mode to raise the output voltage to a target level;
Wherein the PWM control circuit controls the PWM duty based on a control signal in a switching mode and generates a control signal having an initial slope so as to generate a control signal in response to the slope in the initial stage of the switching mode, A mode switching control unit for inducing the duty to be gradually increased; And
And an over-current prevention unit for limiting the current of the DC-DC converter by controlling the PWM duty based on a current limit value during a switching mode,
Wherein the linear charger maintains the mode switching control unit in a reset state during the linear mode and releases the reset of the mode switching control unit to form the slope when the linear mode ends. 2. The apparatus according to claim 1,
Controls the PWM duty to the lowest duty during the linear mode,
And controls the PWM duty to gradually increase from a minimum duty to a maximum duty corresponding to the slope at an initial stage of the switching mode. 2. The apparatus according to claim 1,
An error amplifier for generating an error signal for switching to a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the DC-DC converter;
A ramp controller for generating a control signal having an initial slope in response to an error signal output from the error amplifier; And
And a comparator for controlling a PWM duty based on a sum signal of the current sense signal and the ramp signal of the DC-DC converter in a switching mode and a control signal having an initial slope output from the ramp controller, Device. The lamp controller according to claim 3,
And a variable resistor connected between the output terminal and the ground terminal of the error amplifier to linearly increase the internal resistance value at the beginning of the switching mode to form an initial slope in the control signal. delete The method according to claim 1,
Further comprising a soft start timer for determining a soft start time by setting a current limit value of the overcurrent prevention unit,
Wherein the overcurrent prevention unit generates a current limit signal when the current sense signal fed back from the DC-DC converter reaches a current limit value to control the PWM duty. Linearly increasing an output voltage of the DC-DC converter from an initial level by supplying current in a linear mode;
Determining whether to enter the switching mode in the linear mode based on the change in the output voltage;
Generating a control signal having an initial slope upon entering the switching mode;
Controlling the PWM duty to be gradually increased in response to the slope at the beginning of the switching mode;
Controlling the PWM duty based on a control signal stabilized at one voltage level past the slope after the beginning of the switching mode to raise the output voltage to a target level; And
Limiting the current of the DC-DC converter by controlling the PWM duty based on a current limit value during a switching mode,
Wherein the reset state is maintained during the linear mode, and when the linear mode is terminated, the reset is released to form the slope. 8. The method of claim 7,
Generating an error signal for switching to a switching mode based on a difference between a reference voltage and a feedback voltage obtained from an output voltage of the DC-DC converter upon entering the switching mode, Signal,
And the PWM duty is controlled based on the control signal having the initial slope and the sum signal of the current sense signal and the ramp signal of the DC-DC converter at the beginning of the switching mode. 9. The method of claim 8,
Wherein the initial slope is formed in a control signal output according to the resistance value by linearly increasing the internal resistance value at the beginning of the switching mode.

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