KR20070117917A - Dc/dc step-up converter and control method thereof - Google Patents

Abstract

A DC/DC step-up converter and a control method thereof are provided to avoid an inflow current of an inductor while maintaining a soft start to increase an output voltage from zero. An input part has an inductor(L1) and a first switch(10) electrically connected to the inductor at both ends thereof. A controller has a second switch(11) electrically connected to one end of the input part. An output part is electrically connected to one end of the input part, and has a third switch(12) and a capacitor(Co) for outputting an output signal of the input part. A switch controller controls the first to third switches. When the output voltage of the output part is lower than the input voltage of the input part, the first switch is turned on, the second switch is turned off, and the third switch is switched.

Description

DC / DC step-up converter and control method

1 shows an example of voltage and current characteristics of a conventional DC / DC step-up converter.

Figure 2 shows one embodiment of a DC / DC step-up converter according to the present invention.

FIG. 3 shows the characteristics of the output voltage and the reference voltage of the DC / DC step-up converter shown in FIG.

FIG. 4 illustrates output characteristics of the first and second latches RS1 and RS2 of the DC / DC step-up converter illustrated in FIG. 2 in comparison with the time axis of FIG. 3.

FIG. 5 illustrates the input characteristics of the inductor current of the DC / DC step-up converter shown in FIG. 2 and the inverting input terminal of the PWM comparator PWM_CP in comparison with the time axes of FIGS. 3 and 4.

Figure 6 shows another embodiment of a DC / DC step-up converter according to the present invention.

FIG. 7 shows the characteristics of the output voltage and the reference voltage of the DC / DC step-up converter shown in FIG.

FIG. 8 illustrates output characteristics of the first and second latches RS1 and RS2 of the DC / DC step-up converter illustrated in FIG. 6 in comparison with the time axis of FIG. 7.

FIG. 9 illustrates the input characteristics of the inductor current of the DC / DC step-up converter shown in FIG. 6 and the inverting input terminal of the PWM comparator PWM_CP in comparison with the time axes of FIGS. 7 and 8.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC step-up converter, and more particularly, to a DC / DC step-up converter for starting operation to increase an output voltage from zero.

DC / DC step-up converters are an important part of many power management systems. In many devices, since the supply voltage applied to the device must be higher than that of a commercial battery, a DC / DC step-up converter is used that raises and outputs the input voltage.

Conventional DC / DC step-up converters use a current mode control operation with peak current control. Current mode control operation measures the output voltage at the output load from a feed-back network, such as a resistor divider, and compares it with a reference voltage. Errors corresponding to the compared voltage difference are accumulated, and the accumulated error information is compared with the maximum current information of the inductor. The maximum current information of the inductor can be obtained from the current measuring circuit. This comparison adjusts the duty cycle of the power switch.

However, the conventional DC / DC step-up converter has a problem in starting capacity. Since the feedback output voltage is very small compared to the reference voltage of normal operation, the converter's power switch must be turned on for many periods to quickly increase the output voltage to the desired operating point. Therefore, there is a problem that a large amount of current flows in the inductor, and a large amount of energy is accumulated to cause a risk of damaging the device or degrading performance.

To solve this problem, many conventional DC / DC step-up converters solve the problem by slowly increasing the duty cycle of the power switch to reduce the soft-start in-rush current. Tried to. Figure 1 shows an example of the voltage and current characteristics of a conventional DC / DC converter in which the duty cycle limit is increased in 35%, 45%, 55%, and 65% steps. Therefore, the inductor inrush current is not so large. However, this conventional soft-start method has two problems.

First, since the maximum duty cycle at each stage is determined by the relationship of the output voltage, the switch of the converter is operated at the maximum duty cycle to increase the output voltage. Thus, the current flow is much larger than necessary to increase the output voltage, storing unexpected energy in the inductor.

Second, since the conventional DC / DC step-up converter uses a diode as a rectifier at the output stage, the output voltage does not increase from zero at the soft-start time, but increases from the vicinity of the input voltage level. Therefore, the converter has a predetermined output voltage even in the stopped state. This predetermined output voltage causes leakage of current in the load circuit and unexpected power consumption occurs. Recently, there is a DC / DC converter using a synchronous rectifier using a metal oxide silicon field effect transistor (MOSFET) instead of a diode. The synchronous rectifier keeps the output voltage at zero in the quiescent state, but at soft-start, the duty cycle of the power switch gradually increases, accumulating energy in the inductor and causing excess current to flow. This is because at the start of soft-start, the output voltage is very small compared to the input voltage. Because of this pressure difference, instead of discharging to decrease the current, when the main switch is turned on, the current begins to charge the inductor and is charged until the output switch is turned on. As a result, this current flow creates a problem.

It is an object of the present invention to prevent unexpected excess current from flowing during start-up operation.

Another object of the present invention is that when the output voltage is less than the input voltage, the input voltage itself is sufficient without accumulating energy to raise the output voltage.

It is yet another object of the present invention to provide a soft-start method for removing excess current when the output voltage is less than the input voltage and, incidentally, to control the peak current of the inductor well so that the output voltage becomes greater than the input voltage. In other words, it is to reduce unwanted excess current.

The DC / DC step-up converter according to the present invention includes an input unit including an inductor and a first switch electrically connected to both ends of the inductor; A control unit including a second switch electrically connected to one end of the input unit; An output unit electrically connected to one end of the input unit and including a third switch and a capacitor for outputting an output signal of the input unit; And a switch controller for controlling the first to third switches, wherein the switch controller is turned on in a first section when the output voltage of the output unit is smaller than the input voltage of the input unit. And the second switch is off, and the third switch is controlled to be switched.

Here, the switch control unit, the third switch is switched, the output voltage of the output unit is preferably increased from zero to a predetermined waveform.

The switch controller may control the third switch to be turned off when no current flows through the inductor or when the feedback signal from the output unit is greater than a predetermined reference voltage level.

Here, the switch control unit, in the second period when the output voltage is greater than the input voltage, no current flows in the inductor, or after the third switch is turned off, the second switch is turned on in the next switching cycle Preferably, the first switch is controlled to be turned on before being turned on.

Here, in the second period when the output voltage is greater than the input voltage, it is preferable to control to turn off the second switch when the current flowing through the inductor is greater than a predetermined reference current value.

The switch controller may be configured to generate a switching cycle when no current flows in the inductor or when a feedback signal from the output is greater than a predetermined reference voltage level in a second section when the output voltage is greater than an input voltage. It is preferable to control to turn off the third switch at the end of the.

Here, the switch control unit, in the second period when the output voltage is greater than the input voltage, the first switch to turn off, the second switch to turn off and the third switch for freewheeling (freewheeling) It is desirable to control to turn off.

The switch controller may be configured to turn on the second switch and turn off the first and third switches in a second section when the output voltage is greater than an input voltage, and then the current flowing through the inductor may be generated. When the current value is greater than the set current value, turn off the second switch, turn on the third switch, then turn off the second switch, turn on the third switch, and then When the feedback signal of the output is greater than a predetermined voltage level or when no current flows in the inductor or at the end of a switching cycle, the third switch is turned off, and then the third switch is turned off, Preferably, the first switch is turned on and then sequentially controlled such that the first switch is turned off at the beginning of the next switching cycle.

Here, one end of the inductor is electrically connected to one end of each of the first and third switches, and the other end of the third switch is preferably electrically connected to the capacitor.

Here, the switch control unit, the current sensing circuit for measuring the current flowing in the inductor and the second switch; An output signal feedback unit connected to the output unit to generate the feedback signal; A current ramp control circuit for controlling the slope of the inductor peak current signal; A first comparator for comparing the output signal of the output signal feedback unit with the output signal of the current ramp control circuit; A second comparator for comparing a signal by the current ramp control circuit and an output signal of the current sensing circuit; And an amplifier that, together with the current sensing circuit, provides a control loop to determine the peak current of the inductor.

In this case, the converter preferably includes two or more output units.

A control method of a DC / DC step-up converter according to the present invention includes a control unit including an input unit including an inductor and a first switch electrically connected to both ends of the inductor, and a second switch electrically connected to one end of the input unit. And an output part electrically connected to one end of the input part, the output part including a third switch and a capacitor for outputting an output signal of the input part, and a switch control part controlling the first to third switches. In the up-converter, in a first section in which the output voltage of the output is less than the input voltage of the input, (a) the first switch is on, the second switch is off, and Switching the third switch; And (b) turning off the third switch when no current flows in the inductor or when the feedback signal of the output unit is greater than a predetermined reference voltage level.

Here, in the second period in which the output voltage is greater than the input voltage, (c) no current flows in the inductor, or the second switch is turned on in the next switching cycle after the third switch is turned off. Preferably the step further comprises the step of turning on the first switch.

The method may further include turning off the third switch when the current flowing through the inductor is greater than a predetermined reference current value in a second section in which the output voltage is greater than the input voltage. .

Here, in the second period in which the output voltage is greater than the input voltage, (e) when no current flows through the inductor, or when the feedback signal of the output is greater than a predetermined voltage level, or at the end of a switching cycle, Preferably, the method further includes turning off the three switches.

Here, in a second period in which the output voltage is greater than the input voltage, (f) the first switch is turned on, the second switch is turned off and the third switch is turned on for freewheeling. It is preferable to further comprise the step of -off.

Here, in the second period in which the output voltage is greater than the input voltage, (g) turning on the second switch and turning off the first and third switches; (h) turning off the second switch when the current flowing through the inductor is greater than a predetermined reference current value; (i) turning off the third switch when the feedback signal of the output unit is greater than a predetermined reference voltage level or no current flows in the inductor; (j) the third switch is turned off and the first switch is turned on; And (k) the first switch is turned off at the beginning of the next switching cycle.

The present invention is a direct current / direct current step-up converter (hereinafter simply referred to as a “converter”) that includes a soft-start circuit. The present invention utilizes current-mode control such as soft-start method and peak-current control. The output voltage outputs the desired level of voltage in a predetermined shape from zero without in-rush current to the inductor. This soft-start time is divided into two sections.

In the first section, the freewheel switch, comparator, resistor-feedback network, and ramp generator when the output voltage rising from zero is less than the input voltage after the converter is operated. This allows the converter to act like an LDO (Low Drop Output) without an inductor. In this section the main switch is always off and the freewheel switch is always on. When the output voltage is less than the input voltage, these switches completely remove the inrush current generated by the conventional converter and maintain a sort-start state that causes the output voltage to increase from zero.

The second section of soft-start begins when the output voltage approaches the input voltage. In this section, the main switch is operated to store energy in the inductor of the converter and to raise the output voltage. The peak current is controlled by the peak current control method to limit the peak current of the inductor, the duty-cycle gradually increases, and the output voltage follows the ramp signal proportionally until the final required voltage is reached. .

These two periods of soft-start completely prevent in-rush current into the inductor and increase the output voltage from zero.

The freewheel switch is a switch for connecting both ends of the inductor. When the freewheel switch is turned on, both ends of the inductor are shorted. The word "freewheeling" comes from the phenomenon that when the switch is turned on, the residual current is freewheeled in the loop formed by the switch and the inductor. Since it has an equivalent series resistance (ESR) and the switch has on-resistance, the current charged in the inductor is reduced.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in more detail.

Figure 2 shows one embodiment of a DC / DC step-up converter according to the present invention.

The DC / DC step-up converter according to the present invention includes an input unit including an inductor L1 and a freewheel switch 10 connected to both ends of the inductor L1, and one end of the inductor L1 for controlling an output signal of the input unit. A control unit including a main switch 11 connected to one end thereof, an output unit including an output switch 12 for receiving and outputting an output signal of the input unit and a capacitor Co connected to the other end of the output switch 12, And a switch controller for controlling the switches 10, 11, and 12.

One end of the inductor L1 is electrically connected to one end of the main switch 11 and one end of the output switch 12, respectively, and the other end of the output switch 12 is electrically connected to the capacitor Co.

The switch controller includes a resistor divider R1-R2 that feeds back the output voltage V_out, a current sensing circuit 100 that senses current, a lamp generator 150 that generates a lamp signal Vramp, and a current lamp signal. Current lamp control circuit 140 to control the first latch (RS1) and second latch (RS2), the first and second comparators (CP1, CP2), the third comparator (PWM_CP), amplifier (OTA), digital Block 200 and the first and second switches (S1, S2).

The digital block 200 includes a gate driver 119 and a switch control digital block 120 for controlling the freewheel switch 10, the main switch 11, and the output switch 12. Controlled by frequency generator 130.

In normal operation of the converter, when the output voltage V_out is in a steady-state, the first comparator CP1 and the current ramp control circuit 140 consume current to save energy. In the stationary state without, increases the efficiency.

In this steady state, the output 500 of the first comparator CP1 is cut off and does not affect the operation of the converter. The first switch S1 is connected to the first terminal 1, and the current lamp control circuit 140 does not affect the voltage of the compensation capacitor Cc of the peak current control loop.

The chip-enable signal is a signal for operating the converter, whereby soft-start is initiated. In the present invention, the chip activation signal starts at time zero. When the converter is deactivated, the disable signal resets the first latch RS1 and the second latch RS2 to low, and the first switch S1 and the second switch S2 are respectively reset. It is connected to two terminals (2) and prepares a new soft-start.

V_battery shown in FIGS. 3 and 7 indicates the input voltage V_in.

As described above, the soft-start operation according to the present invention is divided into two sections. In the first section, the output voltage starts from zero and increases to the vicinity of the input voltage. The second section starts after the first section until the output voltage reaches the required voltage level. After that it is stabilized.

First Embodiment

A first embodiment according to the present invention will be described with reference to the drawings shown in Figs.

Figure 2 shows one embodiment of a DC / DC step-up converter according to the present invention.

FIG. 3 shows the characteristics of the output voltage and the reference voltage of the DC / DC step-up converter shown in FIG.

FIG. 4 illustrates output characteristics of the first and second latches RS1 and RS2 of the DC / DC step-up converter illustrated in FIG. 2 in comparison with the time axis of FIG. 3.

FIG. 5 illustrates the input characteristics of the inductor current of the DC / DC step-up converter shown in FIG. 2 and the inverting input terminal of the PWM comparator PWM_CP in comparison with the time axes of FIGS. 3 and 4.

The soft-start in the first embodiment includes two sections.

In the first section, after the converter shown in Fig. 2 is activated, the output voltage V_out is much smaller than the input voltage V_in and increases from zero. That is, V_out <V_in_d. Here, V_in_d = V_in-v, and v means a small voltage assigned to the freewheel switch 10 and the output switch 12 when the output switch 12 is turned on. . This v is set for the safe operation of the soft-start or for safely detecting the end of the first section. As a result, the output of the first comparator CP2 is set to a low state.

Before the chip is activated, the output 500 of the first latch RS1 is in a low state, and the freewheel switch 10 is kept on by the digital block 200, and main is maintained. The switch 11 remains off. Peak current control operation is not performed.

Preferably, the freewheel switch 10 is a PMOS switch, the main switch 11 is an NMMOS switch, and the output switch 12 is a PMOS switch.

Preferably, the first and second latches RS1 and RS2 are reset-set (RS) latches.

The output 320 of the current sensing circuit 100 and the output 520 of the PWM comparator PWM_CP are cut off and are ignored in the operation of the first section.

The output 320 of the current sensing circuit 100 indicates the state of the inductor L1 current. The output 320 of the current sensing circuit 100 is low when the inductor L1 current is 0 or more, and changes to high when the inductor L1 current passes 0. When the output 320 of the current sensing circuit 100 becomes high, the output switch 12 is turned off and the freewheel switch 10 is turned on.

The ramp signal Vramp generated by the ramp generator 150 increases from zero. Since the voltage of the ramp signal Vramp at the soft-start is smaller than the band gap reference voltage V-bandgap, the output of the third comparator CP3 is low, and the output 530 of the second latch RS2 is also low. The second comparator CP2 and the first latch RS1 are also low. The first switch S1 and the second switch S2 are connected to the second terminal 2 by the low signal, which is the output 530 of the second latch RS2.

The reference voltage Vref_ss400 is connected to the non-inverting input terminal (+) of the amplifier OTA and the inverting input terminal (-) of the first comparator CP1, and the reference voltage Vref_ss400 is connected by the current lamp control circuit 140. Is increased along the ramp signal Vramp until the ramp signal Vramp becomes greater than the bandgap reference voltage V_bandgab.

In the first section, the output signal 500 of the first comparator CP1 and the clock signal 131 of the frequency generator 130 are used to control the output switch 12.

At the beginning of each switching cycle, the digital block 200 turns on the output switch 12 and charges the output capacitor Co. The switching cycle is a cycle of switching the free wheel switch 10, the main switch 11, and the output switch 12 for one period. The increase in the output voltage V_output is divided by the resistor divider R1-R2, and the feedback voltage Vfb401 between R1 and R2 is compared with the increasing reference voltage Vref_ss400.

When the feedback voltage Vfb401 is greater than the reference voltage Vref_ss400, the output 500 of the first comparator CP1 is changed from low to high, and the output switch 12 is turned off by the digital block 200. do. When the feedback voltage Vfb401 is still greater than the reference voltage Vref_ss400, the output switch 12 is continuously turned off for a predetermined switching cycle, and the output 500 of the first comparator CP1 is also kept high.

The output switch 12 is turned on at the beginning of a new switching cycle after the reference voltage Vref_ss400, which is increased as the ramp signal Vramp increases, becomes greater than the feedback voltage Vfb401.

In the first section, the main switch 11 is turned off and the freewheel switch 10 is turned on. The freewheel switch 10 remains on, and when the output switch 12 is turned on, both ends of the inductor L1 are connected to help current flow to the output capacitor Co, and the inductor L1 Will charge a very small current. This very small current is discharged by the on-resistance of the freewheel switch 10 and the equivalent series resistance (ESR) of the inductor when the output switch 12 is turned off.

The freewheel current and freewheel switch 10 of the loop formed by the inductor L1 contribute to the loss, but the charged inductor current is so small that it is negligible. Preferably, when the size of the freewheel switch 10 is large enough, the on-resistance of the freewheel switch 10 will be close to zero, and no current will be charged in the inductor L1.

When the output voltage V_out is smaller than the input voltage V_in-v, the converter may include a freewheel switch 10, a first comparator CP1, a resistor-feedback network R1-R2, a digital block 200 and a lamp generator. 150 acts like an LDO without an inductor. Here, v means a small voltage assigned to the freewheel switch 10 and the output switch 12 when the output switch 12 is turned on.

Thus, in the first section, the main switch 11 is always in the off state, and the freewheel switch 10 is always in the on state. When the output voltage V_out is smaller than the input voltage V_in, the state of these switches 10 and 11 causes the output voltage V_out to increase from zero to be maintained in soft-start, while maintaining the conventional Inrush current from the inductor of the converter is completely eliminated.

The second section starts when the output voltage V_out approaches the input voltage V_in. That is, when V_out = V_in-v, the second section is started. Here, v denotes a voltage drop allocated to the output switch 12 and the freewheel switch 10.

In the second section, the main switch 11 is turned on to store energy in the inductor L1 and to raise the output voltage V_Out. The freewheel switch 10 is turned on after the current control circuit 100 senses that the current is zero or after the output switch 12 is turned off and before the main switch 11 is turned on. do.

The peak current is controlled by the peak current control method to limit the peak current of the inductor, the duty-cycle gradually increases, and the output voltage V_out is proportional to the ramp signal Vramp until the desired value is reached. Increase by enemy.

In the second section, since the first switch S1 and the second switch S2 are respectively connected to the second terminal 2, the first switch S1 and the second switch S2 are respectively connected to the current lamp control circuit 140 and the lamp generator 150. Therefore, the reference voltage Vref_ss400 becomes the ramp signal Vramp. The current lamp control circuit 140 may include a buffer, determine the voltage level of the compensation capacitor Cc, and limit the peak current of the inductor L1.

The current lamp control circuit 140 changes the waveform of the reference voltage Vref_ss400 shown in FIG. 3 into the waveform of the ramp signal 3001 having a difference between the low slope and the voltage level shown in FIG. This is in the active region of the amplifier (OTA) output, making it suitable for the current sensing circuit 100. Therefore, the input 300 of the inverting input terminal (-) of the PWM comparator PWM_CP is determined by the current ramp control circuit 140 and is not determined by the output of the amplifier OTA.

In the second section of the first embodiment, the first comparator CP1 adjusts the increasing output voltage V_out and proportionally follows the reference voltage Vref_ss400.

When the peak current information 310 is larger than the input 300 of the inverting input terminal (-) of the PWM comparator PWM_CP, the output 520 of the PWM comparator PWM_CP is changed to a high level, so that the digital block 200 is changed. Through this, the main switch 11 is turned off and the output switch 12 is turned on. As a result, the current is charged in the output capacitor Co.

The first comparator CP1 compares the feedback voltage Vfb401 and the reference voltage Vref_ss400. When the feedback voltage Vfb401 is greater than the reference voltage Vref_ss400 so that the output voltage substantially increases with the reference voltage Vref_ss400 corresponding to the ramp signal Vramp, the output switch 12 is turned off. do.

The freewheel switch 10 is turned on when the main switch 11 and the output switch 12 are turned off, so that a current is freewheeled in the loop of the inductor L1 and the freewheel switch 10.

In the second section, since the output voltage V_out is not smaller than the input voltage V_in, the inductor current is charged while the main switch 11 is turned on, and the peak current is sensed at the end of the duty cycle.

Since the peak inductor current is predetermined and sensed by the current lamp control circuit 140, the inflow current of the inductor L1 is predetermined and is not large, as shown in FIG. By controlling the current lamp control circuit 140, the maximum peak current can be maintained below 400 mA, and this peak current allows the output voltage V_out to reach the desired voltage level.

In the second section according to the first embodiment, the output voltage V_out is formed to increase proportionally along the reference voltage Vref_ss400 by the first comparator CP1, and the peak inductor current is the current lamp control circuit 140. Is determined in advance.

When the ramp signal Vramp reaches the bandgap reference voltage V_bandgap, the output voltage V_out reaches a desired voltage level.

The output of the third comparator CP3 is turned high and the output 530 of the second latch RS2 is set high, as shown in FIG. The first switch S1 and the second switch S2 are respectively connected to the first terminal 1.

As a result, the reference voltage Vref_ss400 reaches a steady state and becomes equal to the bandgap reference voltage V_bandgap. The first switch S1 and the second switch S2 are not changed until the converter is deactivated. At this point in the second section, the amplifier OTA controls the loop of the converter and adjusts the output voltage V_out to a steady state.

As the compensation capacitor Cc has a voltage determined by the current lamp control circuit 140 at the end of the soft-start, the residual energy stored in the inductor L1 is output as shown in Figs. Some overshoot is applied to the voltage V_out. However, as the reference voltage (Vref_ss400) is brought to a steady state, the amplifier (OTA) and the converter loop stabilizes it so that the peak current of the inductor can be directly reduced, and the output voltage (V_out) also reaches the steady state in a short time. Let's do it. The steady state of the reference voltage Vref_ss400 is not limited to the bandgap reference voltage V_bandgap.

Second Embodiment

A second embodiment according to the present invention will be described in detail with reference to the drawings shown in Figs.

Figure 6 shows another embodiment of a DC / DC step-up converter according to the present invention.

FIG. 7 shows the characteristics of the output voltage and the reference voltage of the DC / DC step-up converter shown in FIG.

FIG. 8 illustrates output characteristics of the first and second latches RS1 and RS2 of the DC / DC step-up converter illustrated in FIG. 6 in comparison with the time axis of FIG. 7.

FIG. 9 illustrates the input characteristics of the inductor current of the DC / DC step-up converter shown in FIG. 6 and the inverting input terminal of the PWM comparator PWM_CP in comparison with the time axes of FIGS. 7 and 8.

The second embodiment differs from the first embodiment in the control signal of the first switch S1. As shown in FIG. 6, the first switch S1 is controlled by the output 510 of the first latch RS1, not the output 530 of the first latch RS2. While the first latch RS1 is low, the first switch S1 is connected to the second terminal 2 so that the input of the inverting input terminal (-) of the PWM comparator PWM_CP is determined by the current lamp control circuit. .

The soft-start of the second embodiment is composed of two sections as in the first embodiment, and the first section is the same as the first section in the first embodiment. Therefore, the second section of the second embodiment will be described below.

In the second section, the first comparator CP1 is not used and does not affect the soft-start operation. Therefore, in the stop mode, the output 500 of the first comparator CP1 is shut off and there is no current consumption, thereby increasing efficiency.

In order to bring the input of the inverting input terminal (-) of the PWM comparator (PWM_CP) to the output active region of the amplifier (OTA), the current lamp control circuit 140 is used only in the first section of the soft-start. do. Accordingly, the current lamp control circuit 140 includes a voltage buffer for the fixed voltage obtained from the band gap reference voltage V_bandgap. At the end of the first section, the initial voltage of the compensation capacitor Cc in the second section is set.

When the second section starts and the first latch RS1 is changed to high, the first switch S1 controlled by the output 510 of the first latch RS1 is connected to the amplifier OTA from the second terminal. It is connected to the first terminal 1 to be connected.

The initial voltage of the compensation capacitor Cc is set to the active region of the amplifier OTA by the current lamp control circuit 140 at the end of the first section. The output voltage V_out is rectified while proportionally following the increasing reference voltage Vref_ss400. This control is implemented by a current loop and a voltage loop by the feedback resistor divider R1-R2, the amplifier OTA, the current sensing circuit 100, and the power switches 10, 11, 12.

Cycle cycles the main current (11) turn-on-> sense peak current information with the output voltage (300) of the amplifier (OTA)-> turn the main switch (11) off-> turn the output switch (12) On-> Detect inductor current discharged to zero-> Turn on output switch 12 and turn off freewheel switch 10.

In a certain cycle of the start of the second section, as shown in Fig. 9, the freewheel switch 10 is not turned on, and larger inductor current may flow in the continuous conduction mode (CCM). This is because the output voltage V_out is not much larger than the input voltage V_in, and the start voltage of the compensation capacitor Cc is set to be larger than the voltage level maintained by the small inductor peak current. That is, because the main switch 11 is kept switched during the minimum duty cycle.

However, since the current increases the output voltage V_out and the feedback voltage Vfb increases to be larger than the reference voltage Vref_ss400, the peak current is not so large as 400 mA or less. The loop in the converter causes the output voltage V_out to increase proportionally along the reference voltage Vref_ss400, thereby reducing the current, as shown in FIGS. 7 and 9.

In order for the output voltage V_Out to increase proportionally according to the ramp signal Vramp, as the ramp signal Vramp increases, the voltage / current loop including the amplifier OTA can supply sufficient charge to the output. Increase the peak inductor current.

When the ramp signal Vramp becomes larger than the bandgap reference voltage V_bandgap, the output of the third comparator CP3 is changed to high, and the output of the second latch RS2 is set to high. The reference voltage Vref_ss400 is in a steady state such as the bandgap reference voltage V_bandgap. At this time, the output voltage V_out proportional to the reference voltage Vref_ss400 reaches a desired voltage level and becomes a normal state. Here, the soft-start ends.

When the converter is deactivated and changed to the stop mode, the first latch RS1 and the second latch RS2 are reset low, and the second comparator CP2 and the third comparator CP3 at the next soft-start, respectively. Wait for a high level from the output of

In the present invention, a single output DC / DC step-up converter has been described as a temporary example, but it is also applicable to a soft-start without inrush current in a multiple output DC / DC converter. Accordingly, DC / DC converters with multiple outputs are also included in the scope of the present invention.

In the case of multiple outputs, a plurality of output switches for multiple outputs operate in the same manner as the output switch 12 in the first section and the second section of the embodiment of the present invention.

In the first interval, the other output switches for the multiple outputs may be turned on after the switching cycle begins, or after the output switch 12 is turned off.

In the second section, the other output switches for the multiple outputs may be turned on after the main switch 11 is turned off or after the output switch 12 is turned off.

According to the present invention, the inductor current of the inductor can be completely avoided while maintaining the soft-start which increases the output voltage from zero by the soft-start of two sections.

According to the present invention, it is possible to prevent unexpected excess current from flowing during the start-up operation.

According to the present invention, when the output voltage is smaller than the input voltage, the input voltage itself is sufficient without accumulating energy to raise the output voltage.

According to the present invention, the excess current can be removed when the output voltage is smaller than the input voltage and when the output voltage becomes larger than the input voltage.

Claims (17)

In a DC / DC step-up converter, An input unit including an inductor and a first switch electrically connected to both ends of the inductor; A control unit including a second switch electrically connected to one end of the input unit; An output unit electrically connected to one end of the input unit and including a third switch and a capacitor for outputting an output signal of the input unit; And It includes a switch control unit for controlling the first to third switches, The switch control unit, In a first section when the output voltage of the output unit is less than the input voltage of the input unit, the first switch is on, the second switch is off, and the third switch is switching. DC / DC step-up converter, controlled to be controlled. The method of claim 1, The switch control unit, The third switch is switched, and the output voltage of the output unit is increased from zero to a predetermined waveform. The method of claim 1, The switch control unit, And controlling the third switch to be turned off when no current flows in the inductor or when a feedback signal from the output portion is greater than a predetermined reference voltage level. The method of claim 1, The switch control unit, In the second period when the output voltage is greater than the input voltage, no current flows in the inductor, or the first switch is turned on in the next switching cycle after the third switch is turned off, but before the second switch is turned on in the next switching cycle. DC / DC step-up converter to control the turn on. The method of claim 1, And controlling the second switch to turn off when the current flowing through the inductor is greater than a predetermined reference current value in a second period when the output voltage is greater than an input voltage. The method of claim 1, The switch control unit, In the second period when the output voltage is greater than the input voltage, when no current flows in the inductor, or when the feedback signal from the output is greater than a predetermined reference voltage level or at the end of a switching cycle, the third switch. DC / DC step-up converter, controlling to turn off. The method of claim 1, The switch control unit, In a second period when the output voltage is greater than the input voltage, controlling to turn off the first switch, turn off the second switch and turn off the third switch for freewheeling. , DC / DC step-up converter. The method of claim 1, The switch control unit, In a second period when the output voltage is greater than an input voltage, when the current flowing through the inductor is greater than a preset current value after turning on the second switch, turning off the first and third switches, Turn off the second switch, turn on the third switch, then turn off the second switch, turn on the third switch, and then the feedback signal of the output unit The third switch is turned off when the voltage level is greater than the set voltage level or when no current flows in the inductor or at the end of a switching cycle, the third switch is then turned off, and the first switch is turned off. On and then sequentially controlling the first switch to turn off at the start of the next switching cycle. The method of claim 1, One end of the inductor is electrically connected to one end of each of the first and third switches, and the other end of the third switch is electrically connected to the capacitor. The method of claim 1, The switch control unit, A current sensing circuit measuring current flowing through the inductor and the second switch; An output signal feedback unit connected to the output unit to generate the feedback signal; A current ramp control circuit for controlling the slope of the inductor peak current signal; A first comparator for comparing the output signal of the output signal feedback unit with the output signal of the current ramp control circuit; A second comparator for comparing a signal by the current ramp control circuit and an output signal of the current sensing circuit; And An amplifier providing a control loop with the current sensing circuit to determine the peak current of the inductor Including, DC / DC step-up converter. The method of claim 1, And said converter comprises at least two said outputs. A control unit including an input unit including an inductor and a first switch electrically connected to both ends of the inductor, and a second switch electrically connected to one end of the input unit, and electrically connected to one end of the input unit, and output of the input unit. In the control method of the DC / DC step-up converter comprising an output unit including a third switch and a capacitor for outputting a signal and a switch control unit for controlling the first to third switches, In a first section in which the output voltage of the output unit is smaller than the input voltage of the input unit, (a) said first switch is on, said second switch is off, and said third switch is switching; And (b) turning off the third switch when no current flows in the inductor or when the feedback signal of the output unit is greater than a predetermined reference voltage level. The method of claim 12, In a second section in which the output voltage is greater than the input voltage, (c) turning on the first switch without current flowing through the inductor or after the third switch is turned off but before the second switch is turned on in the next switching cycle. / DC step-up converter control method. The method of claim 12, In a second section in which the output voltage is greater than the input voltage, (d) turning off the third switch when the current flowing in the inductor is greater than a predetermined reference current value. The method of claim 12, In a second section in which the output voltage is greater than the input voltage, (e) a DC / DC step further comprising turning off the third switch when no current flows in the inductor, or when the feedback signal of the output is greater than a predetermined voltage level or at the end of a switching cycle. How to control the up-converter. The method of claim 12, In a second section in which the output voltage is greater than the input voltage, (f) DC / DC step-up converter control further comprising the first switch turning on, the second switch turning off and the third switch turning off for freewheeling. Way. The method of claim 12, In a second section in which the output voltage is greater than the input voltage, (g) turning on the second switch and turning off the first and third switches; (h) turning off the second switch when the current flowing through the inductor is greater than a predetermined reference current value; (i) turning off the third switch when the feedback signal of the output unit is greater than a predetermined reference voltage level or no current flows in the inductor; (j) the third switch is turned off and the first switch is turned on; And (k) further comprising the step of turning off the first switch at the beginning of the next switching cycle.

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