CN210864451U

CN210864451U - DC-DC converter

Info

Publication number: CN210864451U
Application number: CN201921116362.1U
Authority: CN
Inventors: 郝强宇; 王日炎; 周伶俐; 贺黉胤; 万为
Original assignee: GUANGZHOU RUNXIN INFORMATION TECHNOLOGY CO LTD
Current assignee: GUANGZHOU RUNXIN INFORMATION TECHNOLOGY CO LTD
Priority date: 2019-07-16
Filing date: 2019-07-16
Publication date: 2020-06-26
Anticipated expiration: 2029-07-16

Abstract

The utility model discloses a DC-DC converter, including oscillator, error amplifier and supplementary soft start circuit, drive circuit, reference circuit exports first reference voltage to error amplifier, exports second reference voltage to the oscillator; the oscillator receives the feedback voltage after the output voltage is divided and a second reference voltage and generates a square wave and a triangular wave, the square wave is output to the error amplifier, and the triangular wave is output to the comparator; the error amplifier receives the square wave, the feedback voltage and a first reference voltage, and the voltage output by the error amplifier is input into the comparator under the control of the auxiliary soft start circuit; the comparator sends the compared level to the driving circuit, and drives the input voltage to output the output voltage through the BUCK circuit. The utility model discloses a when oscillator, error amplifier and supplementary soft start circuit control go up the electricity oscillator frequency slowly increase, the surge current is gone up in the steady voltage of output reduces, protection load circuit.

Description

DC-DC converter

Technical Field

The utility model relates to an integrated circuit field especially relates to a DC-DC converter.

Background

With the development of portable electronic devices, power management with high efficiency and high quality in integrated circuits becomes more and more important, and thus DC-DC (direct current converter, which refers to a device for converting electric energy of one voltage value into electric energy of another voltage value in a direct current circuit) plays an irreplaceable role in improving the efficiency of a chip power supply. However, during power-up of the DC-DC, rapid charging of the off-chip capacitor can generate a large inrush current in the off-chip inductor. This current may cause the output voltage to momentarily drop or rise, thereby causing the load circuit to malfunction or even break down. To solve this problem, a soft start circuit is required to reduce the power-up surge current.

The main soft start modes at present are: and controlling the duty ratio of a loop, controlling the current value of the inductor and controlling the reference voltage of the error amplifier. The former two soft start modes have the problems of unstable inductive current and low linearity of output voltage in the start stage; the third method uses a large number of digital circuits such as D flip-flops, edge check circuits, T flip-flops, etc. and a digital-to-analog converter DAC to convert digital signals into reference voltages, which can obtain smooth power-on current, but if a smoother reference voltage is desired, the number of required digital circuit bits increases, and the corresponding chip area occupied increases. The on-chip integrated DC-DC is only one of a small part of auxiliary circuits for supplying power to the chip, and the load current is not large, and it is not cost-effective to occupy too much area.

SUMMERY OF THE UTILITY MODEL

In order to overcome the defects of the prior art, the utility model aims to provide a DC-DC converter, through oscillator, error amplifier and supplementary soft start circuit control when going up oscillator frequency slowly increase, the surge current on the reduction of output steady voltage, protection load circuit.

The purpose of the utility model is realized by adopting the following technical scheme:

the DC-DC converter comprises an oscillator, an error amplifier, an auxiliary soft start circuit, a driving circuit and a reference circuit, wherein the reference circuit outputs a first reference voltage to the error amplifier and outputs a second reference voltage to the oscillator; the oscillator receives the feedback voltage obtained by dividing the output voltage and the second reference voltage and generates a square wave and a triangular wave, the square wave is output to the error amplifier, and the triangular wave is output to the comparator; the error amplifier receives the square wave, the feedback voltage and a first reference voltage, and the voltage output by the error amplifier is input into a comparator under the control of the auxiliary soft start circuit; and the comparator outputs the compared level to the driving circuit, and drives the input voltage to output the output voltage through the BUCK circuit.

Further, the error amplifier comprises a soft start circuit and a folded cascode amplifier, the soft start circuit receives the waveform output by the oscillator and charges a capacitor, and the output end of the capacitor is connected with the input end of the folded cascode amplifier; the input end of the folded cascode amplifier is connected with the reference circuit and receives the second reference voltage and the third reference voltage, and the output end of the folded cascode amplifier is connected with the comparator.

Furthermore, the soft start circuit comprises a switching tube and a resistor R₁Resistance R₂The input end of the soft start circuit receives the square wave output by the oscillator and controlsThe switch tube is controlled to be switched on and off; the resistor R₁By folding cascode amplifier M₇Connecting the switch tube to the resistor R₂Connecting the folded cascode amplifier M₈、M₉。

Further, the oscillator comprises a current mirror, a capacitor charge-discharge switching circuit and a feedback voltage control circuit, wherein the current mirror outputs current to be connected with the capacitor charge-discharge switching circuit and outputs triangular waves to the comparator; the feedback voltage control circuit is connected with the current mirror and prolongs the charging time through feedback voltage.

Furthermore, the oscillator also comprises a high-low level charging circuit and a square wave shaping driving circuit, wherein the high-low level charging circuit is connected with the capacitor charging and discharging switch circuit, and the high level and the low level of the triangular wave are controlled through a switch tube; the high-low level control circuit outputs square waves to the square wave shaping driving circuit, and the square wave shaping driving circuit outputs square waves to the error amplifier after being driven by the inverter.

Furthermore, the auxiliary soft start circuit comprises a current mirror, a capacitor and a switching tube; the reference current of the reference circuit controls the charging time of the capacitor through the current mirror, and controls the on and off of the switching tube, so that the output voltage of the error amplifier is controlled.

Further, the driving circuit comprises a logic circuit, wherein the logic circuit receives the level signal output by the comparator, converts the level signal into a PWM signal and outputs the PWM signal to the driving circuit.

Furthermore, the driving circuit comprises a power switch tube, the PWM signal controls the conduction and the cut-off of the power switch tube, the power voltage generates square waves through the conduction and the cut-off of the power switch tube, and the square waves are output through the filter circuit.

Furthermore, a first input end of the feedback voltage control circuit receives a second reference voltage generated by the reference circuit, a second input end of the feedback voltage control circuit receives the feedback voltage, and the charging current is reduced through the differential input pair, so that the charging time is prolonged.

Furthermore, the input end of the square wave shaping driving circuit is connected with the output end of the comparator, and the waveform signal generated by the comparator is subjected to phase inversion driving to output a square wave signal.

Compared with the prior art, the beneficial effects of the utility model reside in that:

the utility model provides a DC-DC converter, at the in-process of chip electricity, the frequency of oscillator can slowly increase, produces a variable square wave of frequency to error amplifier, a variable triangular wave of frequency to comparator, and the small capacitance that intermittent type nature electric current was on giving the integrated chip charges for error amplifier's reference voltage slowly rises. The output end of the DC-DC can slowly rise along with the rise of the reference voltage, namely, the rise time of the output voltage is increased, and the surge current of the inductor can be reduced, so that the effect of soft start is achieved, the upper surge current is reduced, and a load circuit is protected.

Drawings

Fig. 1 is a system block diagram of a DC-DC converter in an embodiment provided by the present invention;

fig. 2 is a feedback voltage controlled oscillator according to an embodiment of the present invention;

FIG. 3a is a waveform of an oscillator output without a soft start circuit;

fig. 3b shows an oscillator output waveform according to an embodiment of the present invention;

fig. 4 is a circuit diagram of a comparator in an embodiment provided by the present invention;

fig. 5 is a schematic diagram of an error amplifier with a soft start circuit according to an embodiment of the present invention;

FIG. 6 shows the error amplifier middle V in the embodiment provided by the present invention_REF1、V_FBAnd V_SA power-up waveform diagram of (1);

fig. 7 is a circuit diagram of an auxiliary soft start circuit according to an embodiment of the present invention;

fig. 8a is a schematic diagram of waveforms of square waves, output voltage and inductor current before the inductor when DC-DC power is applied to the embodiment of the present invention;

fig. 8b is a schematic diagram of waveforms of a square wave before an inductor, an output voltage and an inductor current without a soft start circuit when DC-DC is powered on.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and the detailed description, and it should be noted that the embodiments or technical features described below can be arbitrarily combined to form a new embodiment without conflict.

As shown in fig. 1-8, the present invention provides a DC-DC converter, which comprises an oscillator, an error amplifier, an auxiliary soft start circuit, a driving circuit, and a reference circuit, wherein the reference circuit outputs a first reference voltage to the error amplifier and a second reference voltage to the oscillator; the oscillator receives the feedback voltage obtained by dividing the output voltage and the second reference voltage and generates a square wave and a triangular wave, the square wave is output to the error amplifier, and the triangular wave is output to the comparator; the error amplifier receives the square wave, the feedback voltage and a first reference voltage, and the voltage output by the error amplifier is input into a comparator under the control of the auxiliary soft start circuit; and the comparator outputs the compared level to the driving circuit, and drives the input voltage to output the output voltage through the BUCK circuit.

In the process of electrifying the chip, the frequency of the oscillator is slowly increased to generate a square wave with variable frequency to the error amplifier and a triangular wave with variable frequency to the comparator, and the small capacitor on the integrated chip is charged by intermittent current so that the first reference voltage of the error amplifier slowly rises. The output end of the DC-DC can slowly rise along with the rise of the first reference voltage, the second reference voltage and the feedback voltage, namely the rise time of the output voltage is increased, and the surge current of the inductor can be reduced, so that the effect of soft start is achieved.

Specifically, as shown in FIG. 1, if the voltage V is outputted from the output terminal_OUTIn terms of breaking the loop, the output voltage V_OUTThrough a resistor R₁Resistance R₂The voltage division of (A) generates a feedback voltage V_FBThe first parameter is fed back to the negative input terminal of the error amplifier and generated by the reference circuitReference voltage V_REF1The positive end of the error amplifier is connected; feedback voltage V_FBA second reference voltage V generated by the reference circuit_REF2The output is sent to an oscillator, a square wave with variable frequency is generated and sent to an error amplifier, and a triangular wave with variable frequency is generated and sent to a comparator; the error amplifier generates a voltage V slowly rising with the power-on of the power supply voltage under the control of the auxiliary soft start circuit_EAAnd output to the comparator; level D output after comparison of comparator₁Converted into PWM signal D by logic circuit₂Then the power tube is controlled to be opened or closed through a driving circuit; input voltage V_INThrough a power switch tube M₁、M₂Is turned on and off to generate square wave V_SWAnd then forms a stable output voltage V after being filtered by a filter circuit_OUT。

As shown in fig. 2, a circuit diagram of an oscillator is shown. The oscillator comprises a current mirror, a capacitor charging and discharging switching circuit and a feedback voltage control circuit, wherein the current mirror outputs current to be connected with the capacitor charging and discharging switching circuit and outputs triangular waves to the comparator; the feedback voltage control circuit is connected with the current mirror and prolongs the charging time through feedback voltage. The oscillator also comprises a high-low level charging circuit and a square wave shaping driving circuit, wherein the high-low level charging circuit is connected with the capacitor charging and discharging switch circuit and controls the high level and the low level of the triangular wave through a switch tube; the high-low level control circuit outputs square waves to the square wave shaping driving circuit, and the square wave shaping driving circuit outputs square waves to the error amplifier after being driven by the inverter.

As shown in FIG. 2, I₀Which is an ideal current source, is generated by the reference circuit in the embodiment. M in FIG. 2₁-M₄、M₇、M₈、M₁₁、M₁₂Is a current mirror, M₅、M₆、M₁₃As switching tubes, M₉And M₁₀Is a differential input pair, M₁₄-M₁₉3 inverters are formed. Wherein M is₇W/L of is much greater than M₄，M₄And M₈W/L ratio of 1:1, M₉And M₁₀W/L ratio of 1:1, M₁₁And M₁₂The W/L ratio of (A) is N-1: and N is added. V_FBIs a feedback voltage of DC-DC, V_REF2A reference voltage generated by a reference circuit. I is₁、I₂、I₃、I₄、I₅Respectively is flowing through M₄、M₈、M₉、M₁₀、M₁₁Current between source and drain.

In the prior art, when the circuit of the oscillator is powered on, due to the existence of the capacitor C, the rising of the voltage at the positive end of the comparator, namely the SAW terminal, is slower than the rising of the voltage at the negative electrode, so that the comparator outputs a low level, and thus the CLKN is a low level; switch tube M at this moment₁₃And a switching tube M₆Turn-off, switch tube M₅Turned on, i.e. current I₁The capacitor C will be charged and the SAW voltage ramps up. When the SAW voltage is higher than the negative terminal voltage V₁When the voltage is large, the comparator is turned over, and CLKN is high level; switch tube M at this moment₁₃And a switching tube M₆On, switch tube M₅Closing; the capacitance will pass through the switch tube M₆The tube discharges, but due to the resistance R₃The parallel connection of (A) and (B) reduces the negative voltage of the comparator to V₂Therefore, the SAW voltage is ramped down to V₂. Thus, a triangular wave is obtained by circulating the SAW terminal, as shown in FIG. 3 (a).

In this embodiment, M₈、M₉、M₁₀、M₁₁、M₁₂Form a feedback voltage control circuit, wherein M₉And M₁₀Is a differential input pair, M₈、M₁₁、M₁₂Is a current mirror. In this embodiment, when the circuit is powered up, the DC-DC output voltage is also 0, i.e. the third reference voltage V _FB0, and a second reference voltage V_REF2First powered up, second reference voltage V_REF2Much greater than the third reference voltage V_FBThus current I₂Substantially all flowing into M₉A tube. In this case, the relationship between W and L is:

so that the above-mentioned chargerThe electric current is formed by₁Reduced to (1/N) I₁Namely, the charging time is greatly prolonged, and the power-on frequency is reduced.

When the voltage of the DC-DC output end rises, the third reference voltage V_FBRise, I₄Slowly increase, I₃The charging time is slowly reduced, namely the charging time is slowly increased; the third reference voltage V is used when the DC-DC voltage rises to the target value_FB>Second reference voltage V_REF2Substantially all of the current flowing into M₁₀Tube, I₃At this time, the oscillator returns to the normal frequency, and the DC-DC operates normally, as shown in fig. 3 (b).

At the same time due to the current mirror M₇W/L of is much greater than M₄In addition to the current mirror M₁₁The discharge path is increased, so the discharge time is much shorter than the charge time, i.e. the duty cycle of the output square wave CLK is very large, as the square wave in fig. 3 (b); this has a large attenuation effect on the charging speed of the capacitor in the error amplifier.

The comparator structure in the circuit is shown in fig. 4. M in FIG. 4₁、M₂Is a current mirror, M₃-M₁₂Is a single-ended amplifier structure, M₃、M₄For input pair, M₅-M₈The proportion of (2) determines the hysteresis interval of the comparator, and prevents the comparator from being turned over by mistake due to the burr voltage.

As shown in fig. 5, a circuit diagram of the error amplifier is shown. The error amplifier comprises a soft start circuit and a folding cascode amplifier, the soft start circuit receives the waveform output by the oscillator and charges a capacitor C, and the output of the capacitor C is connected with the input end of the folding cascode amplifier. The input end of the folded cascode amplifier is connected with the reference circuit and receives the second reference voltage and the feedback voltage, and the output end of the folded cascode amplifier is connected with the comparator.

The soft start circuit comprises a switch tube M₅Capacitor C and resistor R₁Resistance R₂The input end of the soft start circuit receives the square wave output by the oscillator, controls the on and off of the switch tube and charges the capacitor C; the resistor R₁By folding cascode amplifier M₇Connecting the switch tube to the resistor R₂Connecting the folded cascode amplifier M₈Folded cascode amplifier M₉。

M in the circuit of FIG. 5₁-M₄、M₆、M₁₀Is a current mirror, M₅Used as a switch, M₈、M₉、M₁₃-M₁₈For folded cascode amplifiers, R₃、M₁₁、M₁₂Forming a bias circuit for providing a gate voltage to the second stage of the amplifier. M₇And M₈、M₉Same size, R₁＝R₂。

When the DC-DC is electrified, a square wave with gradually increasing frequency can be obtained by the oscillator and is input to the CLK end of the circuit. When the power is on, the voltage V at the upper end of the capacitor is generated due to the existence of the capacitor C_SIs 0; controlling M at low level of square wave CLK₅Starting to charge the capacitor C; because the square wave duty ratio is very large and the low level time is very short, the charging speed is greatly reduced, and a slowly rising voltage V can be obtained_S. The positive terminal and the negative terminal of the input of the error amplifier are respectively a first reference voltage V_REF1And a third reference voltage V_FBAnd V and_Sthe power-up curve of (a) is shown in fig. 6.

At the beginning of power-on, because of V_SThe voltage is less than the first reference voltage V_REF1，M₁₇Is substantially entirely comprised of M₇Inflow, i.e. M₇、M₉、R₁、R₂Forming a source degeneration differential pair, with a feedback voltage V_FBVoltage following V_SSlow rise, its equivalent transconductance:

wherein g is_m7Is M₇、M₉Transconductance of the tube.

When V is_SGreater than a first reference voltage V_REF1When M is in contact with₁₇Is substantially entirely comprised of M₈Inflow, i.e. M₈、M₉Form a common differential pair, V_FBFollowing V_REF1Its equivalent transconductance:

G≈g_m8(3)

wherein g is_m8Is M₈、M₉Transconductance of the tube.

At this time, the error amplifier and the DC-DC converter enter a normal operation state. Because the stability of the DC-DC converter requires that the loop unit gain bandwidth needs to be less than 6 times of the frequency of the oscillator, but the frequency of the oscillator is lower during soft start; after source level degradation is used, the equivalent transconductance G follows a third reference voltage V_FBThe unit gain bandwidth of the DC-DC loop is increased in proportion to the transconductance of the error amplifier, so that the unit gain bandwidth of the DC-DC loop is smaller when the power is on, and the stability of the system is improved.

FIG. 7 is a schematic diagram of an auxiliary soft start circuit, which is composed of a simple current mirror M₁-M₄Capacitor C and switch tube M₅Composition is carried out; and the reference current of the reference circuit controls the charging time of the capacitor C through the current mirror, so that the on and off of the switching tube are controlled. Passing a reference current generated by a reference circuit through M₁-M₄The mirror image of the formed current mirror is below 1/100, and an on-chip capacitor C is charged; the charging time of the capacitor C can be reduced by reducing the bias current through mirroring, and the size of the capacitor C can also be reduced; before the capacitor is charged, the switch tube M₅The tube is conducted, the output end is connected to the output end of the error amplifier, and the switching tube M is connected at the moment₅The impedance is very low, the output end is pulled down to the ground potential, and the DC-DC converter cannot be started; the DC-DC converter can prevent the output of wrong level due to instantaneous high level caused by some non-ideal factors during power-on, and the power switching tube is turned on to cause power-on surge current, thereby playing a role in secondary protection. When the capacitor is charged, the switch tube M₅The tube is closed, the impedance is large, the output end of the error amplifier is not affected, and the DC-DC converter can be started and operated normally.

The converter can be integrated in a chip to be a chip, and can normally work at-55 to +125 ℃ in a test. The whole area of the converter circuit is 0.36mm²Wherein, because the converter comprises a feedback voltage control circuit in the oscillator, a soft start circuit in the error amplifier and an auxiliary soft start circuit, the total area of the additional increase is only 0.013mm²The working voltage is 2.5-3.6V, the output voltage is 1.8V, the load current is 400mA, and the working efficiency is 93%. The simulation of DC-DC without soft start and the up surge current in this embodiment is shown in fig. 8. Fig. 8a shows the DC-DC pre-inductor square wave, output voltage and inductor current with soft start, and fig. 8b shows the waveform without soft start. In FIG. 8, VSW is a square wave before the inductance of the DC-DC output terminal, IL is the inductor current, and VOUT is the output voltage. It can be seen that the addition of soft start can slowly increase the frequency of the oscillator during power-on, increase the power-on time, reduce the power-on surge current from 1.164A to 213mA, and make the output voltage curve rise more smoothly.

The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention cannot be limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are all within the protection scope of the present invention.

Claims

The DC-DC converter is characterized by comprising an oscillator, an error amplifier, an auxiliary soft start circuit, a driving circuit and a reference circuit, wherein the reference circuit outputs a first reference voltage to the error amplifier and outputs a second reference voltage to the oscillator; the oscillator receives the feedback voltage obtained by dividing the output voltage and the second reference voltage and generates a square wave and a triangular wave, the square wave is output to the error amplifier, and the triangular wave is output to the comparator; the error amplifier receives the square wave, the feedback voltage and a first reference voltage, and the voltage output by the error amplifier is input into a comparator under the control of the auxiliary soft start circuit; and the comparator outputs the compared level to the driving circuit, and drives the input voltage to output the output voltage through the BUCK circuit.
2. The DC-DC converter of claim 1, wherein the error amplifier comprises a soft start circuit and a folded cascode amplifier, the soft start circuit receiving the waveform output by the oscillator to charge a capacitor, the capacitor output terminal being connected to an input terminal of the folded cascode amplifier; the input end of the folded cascode amplifier is connected with the reference circuit and receives the second reference voltage and the third reference voltage, and the output end of the folded cascode amplifier is connected with the comparator.
3. The DC-DC converter according to claim 2, wherein the soft start circuit comprises a switching tube, a resistor R₁Resistance R₂The input end of the soft start circuit receives the square wave output by the oscillator and controls the on and off of the switch tube; the resistor R₁By folding cascode amplifier M₇Connecting the switch tube to the resistor R₂Connecting the folded cascode amplifier M₈、M₉。
4. The DC-DC converter according to claim 1, wherein the oscillator includes a current mirror, a capacitor charging and discharging switching circuit, and a feedback voltage control circuit, the current mirror outputs a current to the capacitor charging and discharging switching circuit, and outputs a triangular wave to the comparator; the feedback voltage control circuit is connected with the current mirror and prolongs the charging time through the feedback voltage.
5. The DC-DC converter according to claim 4, wherein the oscillator further comprises a high-low level charging circuit and a square wave shaping driving circuit, the high-low level charging circuit is connected with the capacitor charging and discharging switching circuit, and the high level and the low level of the triangular wave are controlled by a switching tube; the high-low level control circuit outputs square waves to the square wave shaping driving circuit, and the square wave shaping driving circuit outputs square waves to the error amplifier after being driven by the inverter.
6. The DC-DC converter of claim 1, wherein the auxiliary soft start circuit comprises a current mirror, a capacitor and a switching tube; the reference current of the reference circuit controls the charging time of the capacitor through the current mirror, and controls the on and off of the switching tube, so that the output voltage of the error amplifier is controlled.
7. The DC-DC converter according to claim 1, further comprising a logic circuit receiving the level signal output from the comparator, converting the level signal into a PWM signal, and outputting the PWM signal to the driving circuit.
8. The DC-DC converter according to claim 7, wherein the driving circuit comprises a power switch tube, the PWM signal controls the power switch tube to be turned on and off, a power supply voltage generates a square wave by the turning on and off of the power switch tube, and the output voltage is output through a filter circuit.
9. A DC-DC converter according to claim 4, wherein the feedback voltage control circuit has a first input terminal receiving the second reference voltage generated by the reference circuit and a second input terminal receiving the feedback voltage, and the charging current is reduced by the differential input pair to increase the charging time.
10. A DC-DC converter according to claim 5, wherein the input terminal of the square wave shaping driving circuit is connected to the output terminal of the comparator, and the waveform signal generated by the comparator is driven in reverse phase to output a square wave signal.