CN112653333A - Digital-analog hybrid control circuit and control method of DC-DC converter - Google Patents
Digital-analog hybrid control circuit and control method of DC-DC converter Download PDFInfo
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- CN112653333A CN112653333A CN202011506830.3A CN202011506830A CN112653333A CN 112653333 A CN112653333 A CN 112653333A CN 202011506830 A CN202011506830 A CN 202011506830A CN 112653333 A CN112653333 A CN 112653333A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
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Abstract
A digital-analog hybrid control circuit and control method of DC-DC converter, change the inductive voltage into the electric current and produce the corresponding frequency signal as the clock of the digital filter through the first current control oscillator, the digital filter calculates according to PWM signal in every clock cycle so as to produce the inductive current digital signal with same phase of inductive current; the output voltage of the DC-DC converter and the reference voltage are converted into a digital signal by the analog-to-digital converter and then processed into a current i by the second transconductance amplifierico2The frequency signal is converted into a clock of a second counter through a second current control oscillator, the second counter starts counting at the falling edge of the PWM signal, and the rising edge of the PWM signal stops counting and is reset, so that a ramp signal is generated; the compensation signal and the ramp signal are added and compared with the inductive current digital signal, and when the inductive current digital signal is smallerAnd controlling the PWM signal to turn high, and after a fixed on-time, turning the PWM signal to turn low.
Description
Technical Field
The invention belongs to the field of integrated circuits and switching power supplies, and relates to a digital-analog hybrid control circuit and a control method of a DC-DC converter.
Background
In recent years, the development of electronic technology is faster and faster, and the requirement on the power performance of the switch is higher and higher. The switch power supply mainly comprises a switch converter and a control circuit. The switching converter mainly has various topological structures such as Buck (Buck), Boost (Boost), Buck-Boost, half-bridge, full-bridge, forward, flyback and the like. The control circuit is used for monitoring the working state and the output signal of the switch converter and simultaneously generating a pulse control signal to control the switch tube so as to regulate the output and stabilize the output. Currently, switching power supplies are continuously developing towards: 1. high frequency, small size, light weight; 2. low noise; 3. and (4) controlling digitalization. The digital control can enable the switching power supply to achieve higher integration level, and can also eliminate the temperature drift of an analog element, so that the switching power supply achieves high anti-interference performance and high reliability. The digital control can set each parameter of the power supply module through programming, so that the modular management of the power supply is more convenient, and the requirements of different applications can be met through flexible configuration.
The traditional pulse width modulation is the most common control method of the switching converter, and the control idea is as follows: an error signal obtained by comparing the output voltage of the converter with the reference voltage is compensated by an error amplifier to generate a control voltage, the control voltage is compared with a sawtooth wave with fixed frequency to obtain a pulse control signal PWM, and the switching-on and switching-off of a switching tube are controlled by a driving circuit to realize the adjustment of the output voltage of the switching converter. In recent years, more and more applications require fast transient response speed of the power supply, for example, when some microprocessors are switched between standby, sleep and normal operation, the transient current rate is as high as 130A/μ s, which requires fast transient response speed of the power supply to meet the load requirement. The traditional control method of pulse width modulation is simple to implement, but the adoption of an error amplifier has the defects of poor transient performance, complex design of a compensation network and the like, so that the requirement of a load is difficult to meet.
Another common control method of a switching converter is pulse frequency modulation, and a conventional Constant On Time (COT) modulation control is one of the more common control methods of the switching converter, which has the following basic ideas: when each switching period starts, the switching tube is conducted, and the output voltage of the converter rises; after the constant on-time, the switching tube is turned off, the output voltage drops, and when the output voltage drops to the reference voltage, the switching tube is turned on again to start a new switching period. Compared with the control of pulse width modulation, the switching converter adopting the control method of pulse frequency modulation has good transient performance, but has poor steady-state accuracy.
Disclosure of Invention
Based on the defects that the traditional switch converter control method cannot give consideration to transient performance and steady-state performance, the invention provides a digital-analog hybrid control circuit and a control method of a DC-DC converter based on a pulse frequency modulation control method, integrates the advantages of analog control and digital control, can give consideration to good transient performance and steady-state performance at the same time, and has a simple control circuit structure and is easy for large-scale integration.
The technical scheme of the control circuit provided by the invention is as follows:
a digital-analog hybrid control circuit of a DC-DC converter comprises an analog control part and a digital control part,
the analog control part comprises a first transconductance amplifier, a second transconductance amplifier, a first current control oscillator, a second current control oscillator and an analog-to-digital converter,
two input ends of the first transconductance amplifier are respectively connected with two ends of an inductor in the DC-DC converter and are used for converting the inductor voltage of the DC-DC converter into a current signal and outputting the current signal;
the input end of the first current control oscillator is connected with the output end of the first transconductance amplifier and is used for generating and outputting a corresponding frequency signal according to the current signal output by the first transconductance amplifier;
two input ends of the second transconductance amplifier are respectively connected with the output voltage of the DC-DC converter and the reference voltage, and are used for converting the error voltage of the output voltage of the DC-DC converter and the reference voltage into an error current signal ierrAnd according to the error current signal ierrGenerating an output current of the second transconductance amplifier;
the input end of the second current control oscillator is connected with the output end of the second transconductance amplifier and is used for outputting a current i according to the second transconductance amplifierico2Generating and outputting corresponding frequency signals;
two input ends of the analog-to-digital converter are respectively connected with the output voltage of the DC-DC converter and the reference voltage and are used for converting the difference value of the output voltage of the DC-DC converter and the reference voltage into corresponding digital error voltage signals;
the digital control part comprises a digital filter, a digital compensator, a first counter, a second counter, an adder, a digital comparator and an on-time generation module,
the clock input end of the digital filter is connected with the frequency signal output by the first current control oscillator, the control input end of the digital filter is connected with the pulse control signal which is output by the on-time generation module and is used for controlling a switching tube in the DC-DC converter, and the output signal of the digital filter is accumulated or subtracted in each clock period of the digital filter and then output to the first input end of the digital comparator; if the pulse control signal in the clock period of the digital filter is at a high level, accumulating the output signals of the digital filter, and if the pulse control signal in the clock period of the digital filter is at a low level, accumulating the output signals of the digital filter;
the input end of the digital compensator is connected with the digital error voltage signal output by the analog-to-digital converter, and the output end of the digital compensator generates a compensation signal;
the clock input end of the second counter is connected with the frequency signal output by the second current control oscillator, the control end of the second counter is connected with the pulse control signal output by the on-time generation module, the second counter starts counting at the falling edge of the pulse control signal, and stops counting and resets at the rising edge of the pulse control signal;
the first input end of the adder is connected with the output end of the digital compensator, the second input end of the adder is connected with the output end of the second counter, and the output end of the adder is connected with the second input end of the digital comparator;
only when the output signal of the digital filter is lower than the output signal of the adder, the output signal of the digital comparator controls the pulse control signal output by the on-time generation module to be turned from low to high and controls the first counter to reset;
the clock input end of the first counter is connected with a system clock, the first counter restarts counting after resetting, and when the counting of the first counter reaches a preset conduction time counting value, the output signal counted by the first counter controls the pulse control signal output by the conduction time generation module to be turned from high to low.
Specifically, the second transconductance amplifier is configured to output the error current signal ierrThe output current generated is iico2＝i0×(i1-ierr)/i1Wherein i0Is a first reference current, i1Is a second reference current; by regulating said first reference current i0And/or the second reference current i1And changing the slope of the output signal of the second counter so as to change the time of the pulse control signal output by the on-time generation module from low to high.
Specifically, the initial value of the output signal of the digital filter is zero.
The invention also provides a corresponding control method based on the digital-analog mixed control circuit of the DC-DC converter, and the technical scheme is as follows:
a digital-analog hybrid control method of a DC-DC converter, which is used for generating and adjusting a pulse control signal for controlling a switching tube in the DC-DC converter, and comprises the following steps in each switching period of the DC-DC converter:
step one, converting the inductive current of the DC-DC converter into an inductive current digital signal with the same phase;
converting the difference value of the output voltage of the DC-DC converter and the reference voltage into a corresponding digital error voltage signal, and generating a compensation signal according to the digital error voltage signal;
step three, converting the output voltage of the DC-DC converter and the error voltage of the reference voltage into corresponding error current signals ierrFor the error current signal ierrProcessed to obtain a control current iico2(ii) a To control the current iico2The corresponding frequency signal obtained by conversion is used as a counting clock to count for the first time, the counting for the first time is started at the falling edge of the pulse control signal of the DC-DC converter, and is stopped and reset at the rising edge of the pulse control signal of the DC-DC converter;
and step four, superposing the counting value of the first counting obtained in the step three with the compensation signal obtained in the step two, and then comparing the superposed value with the inductive current digital signal obtained in the step one, when the comparison result shows that the inductive current digital signal obtained in the step one is lower, controlling the pulse control signal of the DC-DC converter to be turned from low to high, meanwhile, taking a system clock as a counting clock to start counting for the second time from zero, and controlling the pulse control signal of the DC-DC converter to be turned from high to low when the counting value of the second counting reaches a preset conduction time counting value.
Specifically, the specific method for acquiring the inductor current digital signal in phase with the inductor current of the DC-DC converter in the first step is as follows:
5.1, sampling the inductance voltage of the DC-DC converter and converting the inductance voltage into a corresponding current signal;
5.2, converting the current signal obtained in the step 5.1 into a corresponding frequency signal;
5.3, setting the initial value of the inductance current digital signal to be zero, taking the frequency signal obtained in the step 5.2 as a clock signal, and accumulating or subtracting the value of the inductance current digital signal in each clock cycle; and if the pulse control signal of the DC-DC converter in the current clock period is at a high level, accumulating the inductance current digital signal, and if the pulse control signal in the current clock period is at a low level, accumulating the inductance current digital signal.
In particular, according to the error current signal ierrCalculating the control current iico2The following equation is satisfied:
iico2＝i0×(i1-ierr)/i1
wherein i0Is a first reference current, i1Is a second reference current; by regulating said first reference current i0And/or the second reference current i1And changing the time for which the pulse control signal is turned from low to high.
The invention has the beneficial effects that: the invention combines analog control and digital control, when the load of the DC-DC converter changes, the change of the output voltage is immediately converted to the inductive current digital signal and the ramp signal of the current inner loop, and the change of the current digital signal is accelerated by the aid of the simulation, so that the turn-off time of the switching tube in the DC-DC converter can be quickly adjusted, and the transient performance of the DC-DC converter is improved. In addition, the voltage stabilization precision is higher through simulation assistance, and the steady state performance of the system is improved; through a digital control mode, the invention does not need complex loop compensation, simplifies a control loop and enhances the stability and transient response capability of a system.
Drawings
The following description of various embodiments of the invention may be better understood with reference to the following drawings, which schematically illustrate major features of some embodiments of the invention. These figures and examples provide some embodiments of the invention in a non-limiting, non-exhaustive manner. For purposes of clarity, the same reference numbers will be used in different drawings to identify the same or similar elements or structures having the same function.
Fig. 1 is a specific connection diagram of the digital-analog hybrid control circuit applied to a BUCK converter in the embodiment of the invention.
FIG. 2 shows two input signals i of a digital-analog hybrid control circuit in an embodiment of the present inventionL_sen、icAnd a working signal diagram of the pulse control signal PWM.
FIG. 3 is an inductive current signal i of the DC-DC converter when the load of the DC-DC switching converter suddenly changes in the embodimentLPulse control signal PWM and inductive current digital signal i in control circuitL_senDigital signal i output by addercThe simulated waveform of (2).
Fig. 4 is a partially enlarged view of the simulated waveform of fig. 3.
FIG. 5 shows the output voltage Vo and the inductor current i of the DC-DC converter when the load of the DC-DC switching converter suddenly changes in the embodimentLAnd a load current iOThe simulated waveform of (2).
Fig. 6 is a simulation waveform of the load step-down in fig. 5.
Fig. 7 is a simulation waveform of the step on load in fig. 5.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. Specific details of the embodiments described below, such as specific circuit configurations and specific parameters of these circuit elements, are provided to provide a better understanding of the embodiments of the invention, and it will be appreciated by those skilled in the art that embodiments of the invention may be practiced without some of these details or with other methods, components, materials, etc. in combination.
The present invention provides a digital-analog hybrid control circuit and a control method for a DC-DC converter, and the application of the present invention to a BUCK converter is described as an example below, but the control circuit and the control method of the present invention can also be applied to other types of DC-DC converters. As shown in FIG. 1, the BUCK converter comprises two switching tubes S1 and S2 connected between a power supply and ground, the connection of the two switching tubes is connected to the output end of the DC-DC converter through an inductor L, and a pulse control signal PWM generated by the digital-analog hybrid control circuit controls the on and off of the switching tubes S1 and S2 through a driving circuit.
As shown in fig. 1, the digital-analog hybrid control circuit proposed by the present invention includes an analog control portion and a digital control portion, wherein the analog control portion includes a first transconductance amplifier gm1, a second transconductance amplifier gm2, a first current-controlled oscillator ICO1, a second current-controlled oscillator ICO2 and an analog-to-digital converter ADC, and the digital control portion includes a digital filter, a digital compensator PI, a first Counter1, a second Counter2, an adder, a digital comparator CMP and an on-time generation module TON. The method comprises the steps of generating an inductive current digital signal through a first transconductance amplifier gm1, a first current control oscillator ICO1 and a digital filter to form a current inner loop, forming a voltage outer loop through an analog-to-digital converter (ADC), a digital compensator (PI) and an on-time generation module, and performing analog auxiliary ramp signal addition through a second transconductance amplifier gm2, a second current control oscillator ICO2 and a second Counter 2.
Two input ends of a first transconductance amplifier gm1 are respectively connected with two ends of an inductor L in the DC-DC converter, and the first transconductance amplifier gm1 samples the voltage of the two ends of the inductor L in the DC-DC converter, converts the inductor voltage into a current signal and then connects the current signal to the input end of a first current control oscillator ICO 1; the first current control oscillator ICO1 is used for generating a corresponding frequency signal according to the current signal output by the first transconductance amplifier gm1 and outputting the frequency signal to the clock input end of the digital filter; the control input end of the digital filter is connected with the pulse control signal PWM output by the conduction time generation module, and the output end of the digital filter generates an inductive current digital signal iL_sen。
The digital filter generates an inductor current digital signal iL_senThe process comprises the following steps:
the transfer function of the digital filter is
Where Y (z) represents the output of the digital filter, X (z) represents the input of the digital filter, K is the gain of the digital filter, TPIs the product of the sample time and the compensation pole. The digital filter uses the frequency signal output by the first current-controlled oscillator ICO1 as a clock signal, under which the digital filter outputs the inductive current digital signal i to it every clock periodL_senThe value of (a) is calculated once, if the pulse control signal PWM generated by the conduction time module is high in each calculation, the input X (z) is set to be 1, and if the pulse control signal PWM is low, the input X (z) is set to be-1; if the actual inductor current is initially 0, the initial value of the output Y (z) is preferably set to 0, when X (z) is 1, the output Y (z) is incremented up, and when X (z) is-1, the output Y (z) is decremented down, thereby generating an inductor current digital signal i in phase with the inductor current signalL_sen。
Two input ends of the second transconductance amplifier gm2 are respectively connected with the output voltage U of the DC-DC converter0And a reference voltage VrefThe second transconductance amplifier gm2 converts the output voltage U of the DC-DC converter0And a reference voltage VrefIs converted into an error current signal ierrAnd for the error current signal ierrProcessing is carried out to obtain the output current i of the second transconductance amplifier gm2ico2. The input terminal of the second current controlled oscillator ICO2 is connected with the output current i of the second transconductance amplifier gm2ico2And according to the output current i of the second transconductance amplifier gm2ico2Generating a corresponding frequency signal and then connecting the clock input end of the second Counter 2; the control terminal of the second Counter2 is connected to the pulse control signal PWM outputted from the on-time generating module, and the output terminal thereof generates a ramp signal.
The ramp signal is generated by the following process:
output voltage U of DC-DC converter0And a reference voltage VrefThe error current signal i is obtained by the second transconductance amplifier gm2err＝gm2×(Vref-U0) Gm2 is a second transconductance amplifierTransconductance of the device, for error current signal ierrIs processed to obtain iico2According to iico2The generated frequency signal is used as a counting clock signal of the second Counter2, and starts counting at the falling edge of the pulse control signal PWM, stops counting at the rising edge of the pulse control signal PWM and resets, and a new counting is not started until the falling edge of the next pulse control signal PWM comes, so as to obtain the ramp signal.
Due to iico2Is to ierrProcessed, i.e. the output current i of the second transconductance amplifier gm2ico2Is compared with the error current signal ierrThe correlated signal can be obtained by introducing a reference current and correlating it with an error current signal ierrAdded or multiplied to obtain a current iico2So that a current iico2Is adjusted. For example, some embodiments introduce a first reference current i0And ierrAdd to obtain iico2＝i0+ierr(ii) a Still other embodiments introduce the first reference current i0And a second reference current i1Obtaining iico2＝i0×(i1-ierr)/i1And of course, other calculation methods can be adopted. Due to the introduction of the reference current, the output current i of the second transconductance amplifier gm2 is enabledico2Is compared with the error current signal ierrCan be adjusted by the reference current. Preferably iico2＝i0×(i1-ierr)/i1Thus by adjusting the first reference current i0And/or a second reference current i1The time for which the pulse control signal PWM is turned from low to high can be changed, and the precision of the multiplication form is higher.
Two input ends of the analog-to-digital converter ADC are respectively connected with the output voltage U of the DC-DC converter0And a reference voltage VrefFor converting the output voltage U of the DC-DC converter0And a reference voltage VrefThe difference value is converted into a corresponding digital error voltage signal, and the digital error voltage signal passes through a digital compensator to obtain a digital compensation signal. The adder outputs the digital compensation signal from the digital compensatorAdding the slope signal output by the second Counter2 to obtain a digital signal ic。
Two input terminals of the digital comparator CMP are connected with a digital signal icAnd inductor current digital signal iL_senThe output signal is used to control the on-time generation module and the first Counter 1. In some embodiments, the digital signal icConnecting the positive input terminal of the digital comparator CMP to convert the inductor current digital signal iL_senConnecting the negative input of the digital comparator CMP, then at iL_senIs less than icWhen the output signal of the digital comparator CMP is high, otherwise, it is low; the pulse control signal PWM outputted from the on-time generation module is controlled to be turned from low to high at the rising edge of the output signal of the digital comparator CMP, and controls the first Counter1 to reset. If the other way round, the digital signal i is transmittedcConnecting negative input terminal of digital comparator CMP to obtain inductor current digital signal iL_senConnecting the positive input of the digital comparator CMP, then at iL_senIs less than icWhen the output signal of the digital comparator CMP is low, otherwise, it is high; the pulse control signal PWM outputted from the on-time generation module is controlled to be turned from low to high at the falling edge of the output signal of the digital comparator CMP, and controls the first Counter1 to reset. The connection of the two inputs of the digital comparator CMP does not affect the scope of protection of the invention.
The control process of the pulse control signal PWM is as follows:
digital comparator CMP at iL_senIs less than icThe first Counter1 generates a pulse signal to control the pulse control signal PWM to be turned from low to high, and simultaneously outputs a reset signal RST of the first Counter to reset the first Counter1, a clock input end of the first Counter is connected with the system clock SYS _ CLK, the system clock SYS _ CLK is used as a counting clock to restart counting after the first Counter1 is reset, and when the counting of the first Counter1 reaches a preset on-time counting value, the first Counter1 outputs a signal RST _ TON to control the pulse control signal PWM output by the on-time generation module to be turned from high to low, and the pulse control signal PWM is not turned to high again until a pulse signal of a next digital comparator comes. So as to circulate the above-mentioned steps,a continuous pulse control signal PWM is obtained.
Resetting the first Counter1 when the signal RST is in the first state, and not affecting the first Counter1 when the signal RST is in the second stateL_senIs less than icAt this time, the signal RST changes to the first state, and after a system clock SYS _ CLK, the signal RST changes to the second state. When the signal RST _ TON is in the first state, the pulse control signal PWM is controlled to be turned from high to low, and when the signal RST _ TON is in the second state, the pulse control signal PWM is not affected, and when the first Counter1 counts a predetermined fixed on-time count value, the signal RST _ TON is changed to the first state until the pulse signal RST _ TON of the next digital comparator CMP is changed to the second state. In some embodiments, the first state of the signal may be a low level, and the second state may be a high level, or vice versa, without affecting the scope of the present invention.
FIG. 2 is a waveform diagram showing the operation of two input signals and the pulse control signal PWM of the digital comparator according to the embodiment of the present invention, and the digital signal iL_senThe simulation is that the inductive current signal is in phase with the inductive current signal and has the same variation trend; digital signal icThe current-controlled oscillator is obtained by adding a compensation signal and a ramp signal, wherein the compensation signal is a DC value, one switching period of the DC-DC converter is updated by a digital compensator for one time, the ramp signal is generated by a second Counter2 under the frequency signal output by a second current-controlled oscillator ICO2, and the current-controlled oscillator introduces a first reference current i0And a second reference current i1For error current signal ierrIs processed such that the input signal i of the second current controlled oscillator ICO2ico2＝i0×(i1-ierr)/i1Thus by regulating the first reference current i0The slope of the steady-state ramp signal generated by the second Counter2 can be changed to adjust the second reference current i1The error current signal i can be changederrTo iico2The adjustment rate of the slope signal is changed, and when an error voltage exists, a corresponding error current is generated, so that the adjustment rate of the slope signal is changedVariable slope, pair iL_senAnd icIs changed at the collision point of iL_senIs less than icThen, after a fixed on-time, the pulse control signal PWM is turned down until the next iL_senIs less than icWhen this occurs, the pulse control signal PWM is turned up again, thus regulating the first reference current i0And/or a second reference current i1The time during which the pulse control signal PWM is turned from low to high can be changed.
Simulation analysis was performed on this example using MATLAB/Simulink software, and the results are as follows.
FIG. 3 shows an inductive current i of a switching converter according to an embodiment of the present invention when a load suddenly changesLInductor current digital signal iL_senDigital signal icAnd a simulated waveform of the pulse control signal PWM. Simulation conditions of the present embodiment: input voltage Vg5V, reference voltage Vref3.3V, inductance L0.18 uH, capacitance C1720 uF (equivalent series resistance 20m Ω), constant on-time Ton0.66 us. As can be seen from FIG. 3, the inductor current digital signal iL_senAnd the inductor current iLThe change direction is consistent when the load is suddenly changed.
Fig. 4 is a partially enlarged view of the simulated waveform of fig. 3 according to an embodiment of the present invention. In fig. 4, the inductor current digital signal i can be seenL_senAnd the inductor current signal iLPhase identity, where the inductor current fluctuates, iL_senProducing the same ripple, the digital signal icFrom the addition of the compensation signal and the ramp signal, it can be seen that the ramp signal is only generated at times when the pulse control signal PWM is low, iL_senIs less than icThe digital comparator generates a pulse signal and then the pulse control signal PWM goes high again. Transient response can be further improved through the ramp signal, and the working waveform shows that the transient response control circuit has better transient performance.
FIG. 5 shows an output voltage V of a switching converter according to an embodiment of the present invention when a load suddenly changes0Inductor current iLAnd a load current iOThe simulated waveform of (2). The load current is stepped from 30A to 21A at 0.832ms and the load is stepped from 21A to 30A at 1.668 ms. As can be seen from FIG. 5, the average output voltage is stabilized at 3.3V, the peak-to-peak value of the output voltage is 4.5mV, and the output voltage is adjusted and recovered quickly, so that the invention has high voltage stabilization precision and steady-state performance.
Fig. 6 is a simulated waveform of fig. 5 at a step-down of the load according to an embodiment of the present invention. In fig. 6, at 0.832ms, when the load changes from 30A to 21A in a step change, the output voltage can be quickly adjusted to return to the steady state, the adjustment time is 11us, and the peak-to-peak fluctuation of the output voltage is 19 mV.
Fig. 7 is a simulated waveform of the load of fig. 5 at a step in accordance with an embodiment of the present invention. In fig. 7, when the load is changed from 21A to 30A in a step manner at 1.668ms, the output voltage can be quickly adjusted to recover the steady state, the adjustment time is 11us, and the peak-to-peak fluctuation of the output voltage is 17mV, so that the control method provided by the invention has good load transient performance.
In summary, the present invention provides a digital-analog hybrid control circuit and a control method for a DC-DC converter, in which a first transconductance amplifier gm1 samples an inductor voltage of the DC-DC converter and converts the inductor voltage into a current signal, and the current signal is further mapped to a frequency signal by a first current controlled oscillator ICO1, a digital filter takes the frequency signal generated by the first current controlled oscillator ICO1 as a clock, and the digital filter controls the inductor current digital signal i per clock cycle under the control of a pulse control signal PWML_senUpdate is performed with PWM high, iL_senCumulative, PWM is low, iL_senIs subtracted to obtain a digital signal i in phase with the inductor currentL_sen(ii) a Simultaneously, the difference value of the output voltage of the DC-DC converter and the reference voltage is sampled by the analog-to-digital converter ADC to obtain a digital error voltage signal verrDigital error voltage signal verrObtaining a compensation signal after the compensation signal passes through a digital compensator PI and outputting the compensation signal to one input end of the adder; the second transconductance amplifier gm2 samples the difference between the output voltage of the DC-DC converter and the reference voltage to obtain an error current signal ierr，ierrAnd a reference current signal i0、i1Obtaining i by multiplicationico2＝i0×(i1-ierr)/i1，iico2The frequency signal converted by the second current controlled oscillator ICO2 is outputted to the second Counter2 as the counting clock of the second Counter2, the second Counter2 starts counting at the time of the falling edge of the pulse control signal PWM, stops counting and resets at the time of the rising edge of the pulse control signal PWM, the generated ramp signal is outputted to the other input end of the adder, the adder adds the compensation signal and the ramp signal to obtain the digital signal ic(ii) a Digital comparator CMP for converting the digital signal icAnd inductor current digital signal iL_senComparing, controlling the pulse control signal PWM generated by the on-time generation module TON to be turned high according to the comparison result when iL_senIs less than icWhen the first counter is started, the pulse control signal PWM signal is turned from low to high, the on-time generation module TON outputs a reset signal RST of the first counter to be low, and the RST signal is changed to be high after a system clock SYS _ CLK; the RST signal at low level resets the first Counter1, the first Counter1 resets and then counts again with the system clock SYS _ CLK as a counting clock, so that the RST signal at low level is output when a preset fixed on-time count value is counted, the RST signal at low level turns the pulse control signal PWM from high to low, and the pulse control signal PWM is turned high again and the RST signal at high again until the next pulse signal of the digital comparator CMP comes over. With this cycle, a stable PWM signal is generated to control the switching converter. The DC-DC converter adopts a control time sequence consisting of constant conduction, disconnection and constant conduction to control the conduction and the disconnection of a switching tube of the switching converter.
According to the embodiment and the simulation analysis, when the load of the DC-DC converter changes, the change of the output voltage is immediately converted to the current inner loop and the ramp signal, and the change of the current digital signal is accelerated due to the analog assistance, so that the conversion of the pulse signal of the comparator is accelerated, the change of the turn-off time is accelerated, and the transient performance of the converter is improved; in addition, the invention has high voltage stabilization precision, and the system does not need complex loop compensation, thereby simplifying the control loop.
Those skilled in the art can make various other specific changes and combinations based on the teachings of the present invention without departing from the spirit of the invention, and these changes and combinations are within the scope of the invention.
Claims (6)
1. A digital-analog hybrid control circuit of a DC-DC converter is characterized by comprising an analog control part and a digital control part,
the analog control part comprises a first transconductance amplifier, a second transconductance amplifier, a first current control oscillator, a second current control oscillator and an analog-to-digital converter,
two input ends of the first transconductance amplifier are respectively connected with two ends of an inductor in the DC-DC converter and are used for converting the inductor voltage of the DC-DC converter into a current signal and outputting the current signal;
the input end of the first current control oscillator is connected with the output end of the first transconductance amplifier and is used for generating and outputting a corresponding frequency signal according to the current signal output by the first transconductance amplifier;
two input ends of the second transconductance amplifier are respectively connected with the output voltage of the DC-DC converter and the reference voltage, and are used for converting the error voltage of the output voltage of the DC-DC converter and the reference voltage into an error current signal ierrAnd according to the error current signal ierrGenerating an output current i of the second transconductance amplifierico2；
The input end of the second current control oscillator is connected with the output end of the second transconductance amplifier and is used for outputting a current i according to the second transconductance amplifierico2Generating and outputting corresponding frequency signals;
two input ends of the analog-to-digital converter are respectively connected with the output voltage of the DC-DC converter and the reference voltage and are used for converting the difference value of the output voltage of the DC-DC converter and the reference voltage into corresponding digital error voltage signals;
the digital control part comprises a digital filter, a digital compensator, a first counter, a second counter, an adder, a digital comparator and an on-time generation module,
the clock input end of the digital filter is connected with the frequency signal output by the first current control oscillator, the control input end of the digital filter is connected with the pulse control signal which is output by the on-time generation module and is used for controlling a switching tube in the DC-DC converter, and the output signal of the digital filter is accumulated or subtracted in each clock period of the digital filter and then output to the first input end of the digital comparator; if the pulse control signal in the clock period of the digital filter is at a high level, accumulating the output signals of the digital filter, and if the pulse control signal in the clock period of the digital filter is at a low level, accumulating the output signals of the digital filter;
the input end of the digital compensator is connected with the digital error voltage signal output by the analog-to-digital converter, and the output end of the digital compensator generates a compensation signal;
the clock input end of the second counter is connected with the frequency signal output by the second current control oscillator, the control end of the second counter is connected with the pulse control signal output by the on-time generation module, the second counter starts counting at the falling edge of the pulse control signal, and stops counting and resets at the rising edge of the pulse control signal;
the first input end of the adder is connected with the output end of the digital compensator, the second input end of the adder is connected with the output end of the second counter, and the output end of the adder is connected with the second input end of the digital comparator;
only when the output signal of the digital filter is lower than the output signal of the adder, the output signal of the digital comparator controls the pulse control signal output by the on-time generation module to be turned from low to high and controls the first counter to reset;
the clock input end of the first counter is connected with a system clock, the first counter restarts counting after resetting, and when the counting of the first counter reaches a preset conduction time counting value, the output signal counted by the first counter controls the pulse control signal output by the conduction time generation module to be turned from high to low.
2. The digital-to-analog hybrid control circuit of a DC-DC converter according to claim 1, wherein the second transconductance amplifier is configured to output the error current signal ierrThe output current generated is iico2＝i0×(i1-ierr)/i1Wherein i0Is a first reference current, i1Is a second reference current;
by regulating said first reference current i0And/or the second reference current i1And changing the slope of the output signal of the second counter so as to change the time of the pulse control signal output by the on-time generation module from low to high.
3. The digital-to-analog hybrid control circuit of a DC-DC converter according to claim 1 or 2, wherein an initial value of the digital filter output signal is zero.
4. A digital-analog hybrid control method of a DC-DC converter, which is used for generating and adjusting a pulse control signal for controlling a switching tube in the DC-DC converter, and is characterized in that in each switching period of the DC-DC converter, the digital-analog hybrid control method comprises the following steps:
step one, converting the inductive current of the DC-DC converter into an inductive current digital signal with the same phase;
converting the difference value of the output voltage of the DC-DC converter and the reference voltage into a corresponding digital error voltage signal, and generating a compensation signal according to the digital error voltage signal;
step three, converting the output voltage of the DC-DC converter and the error voltage of the reference voltage into corresponding error current signals ierrFor the error current signal ierrProcessed to obtain a control current iico2(ii) a To control the current iico2The corresponding frequency signal obtained by conversion is used as a counting clock to count for the first time, the counting for the first time is started at the falling edge of the pulse control signal of the DC-DC converter, and is stopped and reset at the rising edge of the pulse control signal of the DC-DC converter;
and step four, superposing the counting value of the first counting obtained in the step three with the compensation signal obtained in the step two, and then comparing the superposed value with the inductive current digital signal obtained in the step one, when the comparison result shows that the inductive current digital signal obtained in the step one is lower, controlling the pulse control signal of the DC-DC converter to be turned from low to high, meanwhile, taking a system clock as a counting clock to start counting for the second time from zero, and controlling the pulse control signal of the DC-DC converter to be turned from high to low when the counting value of the second counting reaches a preset conduction time counting value.
5. The digital-analog hybrid control method of the DC-DC converter according to claim 4, wherein the specific method for acquiring the inductor current digital signal in phase with the inductor current of the DC-DC converter in the first step is as follows:
5.1, sampling the inductance voltage of the DC-DC converter and converting the inductance voltage into a corresponding current signal;
5.2, converting the current signal obtained in the step 5.1 into a corresponding frequency signal;
5.3, setting the initial value of the inductance current digital signal to be zero, taking the frequency signal obtained in the step 5.2 as a clock signal, and accumulating or subtracting the value of the inductance current digital signal in each clock cycle; and if the pulse control signal of the DC-DC converter in the current clock period is at a high level, accumulating the inductance current digital signal, and if the pulse control signal in the current clock period is at a low level, accumulating the inductance current digital signal.
6. The digital-analog hybrid control method of the DC-DC converter according to claim 4 or 5, characterized in thatAccording to said error current signal ierrCalculating the control current iico2The following equation is satisfied:
iico2＝i0×(i1-ierr)/i1
wherein i0Is a first reference current, i1Is a second reference current; by regulating said first reference current i0And/or the second reference current i1And changing the time for which the pulse control signal is turned from low to high.
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