CN100352155C - Sawtooth wave generating device in chip of electric current mode PWM DC-DC converter - Google Patents

Abstract

The present invention relates to a saw-tooth wave generating device which is integrated in chips (1 and 2) of a PWM DC-DC converter with a current mode. The present invention is characterized in that the saw-tooth wave generating device comprises a low-pass filter (3) and a voltage-current converter of which the input ends are orderly connected in series with and control clock signals CLK of DC-DC conversion switch circuits in the chips of the converter, and a controlled switch, a capacitor Cr and an electric earth which are connected in parallel. The device is integrated in the chips (1 and 2) which are supplied with electricity by VIN or VOUT which is obtained directly, obtains D*VIN or D* VOUT by the low-pass filter in the device to further obtain the feedback information required by the device according to the relation of the D* VIN and the D* VOUT so as to output compensation saw-tooth waves. Thus the device can obtain the other VOUT or VIN which can not be directly obtained without adding terminal pins of the chips so as to reduce the production cost and the installation cost of the chips and increase the integral working stable degree of the chips.

Description

Sawtooth waveforms generating means in the current mode PWM DC-DC converter chip

Technical field

The present invention relates to switch power technology, particularly method for generation that is used for the adaptive equalization sawtooth waveforms and the device thereof in the current mode PWM DC-DC converter.

Background technology

Pulse-width modulation Pulse Width Modulation is called for short PWM, the main PWM technology that adopts in the switching mode DC-DC converter, and its application is very extensive.PWM control is divided into current-mode and voltage mode two class modes.Current-mode has good stability, compensates advantages such as simple, has obtained using widely in the PWM power supply.

The type is boosted and decompression DC-DC converter, specifically as depicted in figs. 1 and 2, when the duty ratio D of the CLK of control switch circuit signal＞50%, the current-mode DC-DC converter may not steady operation, and saw-toothed wave generator is used for producing the sawtooth waveforms of doing compensation so that system can steady operation.In order to allow system stability work, the equivalent output current slope of sawtooth waveforms must satisfy formula [1] and require:

$\left|\mathrm{\&alpha;}\right|=|-\frac{m_2-m_a}{m_1+m_a}|<1---\left[1\right]$

In the formula [1], m _aEquivalent output current slope, m for sawtooth waveforms ₁Be slope, the m of electric current I IN during switch conduction ₂Be the slope of electric current I OUT at the switch blocking interval.To different DC-DC converter, m ₁And m ₂Value as shown in Table 1:

m _aUsually select:

m _a＝0.5m ₂-------------[2]

To guarantee | α | less than 1, shown in [3]:

$\left|\mathrm{\&alpha;}\right|=|-\frac{m_2-0.5m_2}{m_1+0.5{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C20051003707000132.png"\; state="\{\{state\}\}">m</figure-callout>}}_2}|=\frac{0.5m_2}{m_1+m_2}---\left[3\right]$

By table one as seen, m ₁And m ₂Value is determined by the value of VIN, VOUT and L.Yet VIN and VOUT have uncertain value usually, and this just brings great difficulty to compensation, thereby cause the unsteadiness of system.

When VIN and VOUT were changed, system can steady operation, m _aNeed change i.e. adaptive equalization with the variation of VIN and VOUT.

With the booster converter is example, and the adaptive equalization of adopting above table one and formula [2] to describe principle need be known the variation of VIN and VOUT, changes the equivalent output current slope m of sawtooth waveforms by the variation that detects VIN and VOUT _aTo reach adaptive equalization.

With the buck converter is example, and the adaptive equalization of adopting above table one and formula [2] to describe principle need be known the variation of VOUT, changes the equivalent output current slope m of sawtooth waveforms by the variation that detects VOUT _aTo reach adaptive equalization.

Yet as Fig. 1, in voltage boosting dc-DC converter chip 1, VOUT can directly obtain, and VIN inserts in the chip 1 by inductance, therefore can not directly obtain or need increase in addition the directly acquisition of terminal pin of chip 1; As Fig. 2, in decompression DC-DC converter chip 2, VIN can directly obtain, and VOUT draws from chip 2 by inductance, therefore can not directly obtain or need increase in addition the directly acquisition of terminal pin of chip 2.

Summary of the invention

The technical issues that need to address of the present invention are, how a kind of sawtooth waveforms generating means that is integrated in the current mode PWM DC-DC converter chip is provided, and the terminal pin that need not increase converter chip in addition can provide the adaptive equalization that meets the demands sawtooth waveforms.

At first, the key of dealing with problems is described: when the DC-DC converter steady operation, VIN, VOUT and D (the conducting duty ratio of switching circuit) are with having a fixing relation, as shown in Table 2:

The above-mentioned technical problem of the present invention solves like this, and a kind of sawtooth waveforms generating means is provided, and is integrated in the current mode PWM DC-DC converter chip, it is characterized in that, comprising:

Low pass filter, input connect the clock signal clk of the inner dc-dc conversion switching circuit of this converter chip of control;

Voltage to current converter, input is connected with the output of described low pass filter;

Controlled switch and capacitor C r in parallel, a ground connection, the other end connects the output of described voltage to current converter, and described controlled switch is pressed certain hour frequency closure/disconnection.

According to sawtooth waveforms generating means provided by the invention, described converter chip is the chip that boosts, and the power supply of this chip that boosts is provided by its output voltage VO UT.The high level of clock signal clk is VOUT like this, can obtain D*VOUT by low pass filter, has promptly obtained the value of VOUT-VIN according to table two, obtains the required feedback information of sawtooth waveforms generating means.

According to sawtooth waveforms generating means provided by the invention, described converter chip is the step-down chip, and the power supply of this step-down chip is provided by its input voltage VIN.The high level of clock signal clk is VIN like this, can obtain D*VIN by low pass filter, has promptly obtained the value of VOUT according to table two, obtains the required feedback information of sawtooth waveforms generating means.

According to sawtooth waveforms generating means provided by the invention, direct feeding system is the simplest, also can take other modes to guarantee that the high level of CLK obtains analog value.

The low pass filter that connects clock signal clk is a unique portion of the present invention:

According to sawtooth waveforms generating means provided by the invention, described low pass filter is the above RC passive low ventilating filter of single order or single order.

According to sawtooth waveforms generating means provided by the invention, described low pass filter is the above active low-pass filter of single order or single order.This scheme cost is minimum.

According to sawtooth waveforms generating means provided by the invention, described active low-pass filter comprises but is not restricted to RC or C active low-pass filter.

Following circuit part is the present invention and the basic identical or similar portions of existing sawtooth waveforms generating means, finishes basic identical or similar effect:

According to sawtooth waveforms generating means provided by the invention, described voltage to current converter comprises but is not restricted to controlled mirror current source.

According to sawtooth waveforms generating means provided by the invention, it is one amplifier that the input of described controlled mirror current source is provided with voltage amplification factor.Increase current output, the input voltage of controlled end can not changed with the load size.

According to sawtooth waveforms generating means provided by the invention, the control end of described controlled switch connects the clock signal clk of the inner dc-dc conversion switching circuit of described converter chip.

According to sawtooth waveforms generating means provided by the invention, the control end of described controlled switch connects the output of described converter chip internal oscillator.

Sawtooth waveforms generating means provided by the invention, be integrated in the current mode PWM DC-DC converter chip, this chip is by a kind of VIN that can directly obtain or VOUT power supply, obtain D*VIN or D*VOUT by the low pass filter that is integrated in this device, thereby compensate sawtooth waveforms according to D, the VIN of table two description and required all feedback informations outputs of deriving means that concern of VOUT; This device need not increase the chip lead pin and obtains VOUT or the VIN that another kind can not directly obtain like this, reduces chip and generates and installation cost, and improved the overall work stability.

Description of drawings

Further the present invention is described in detail below in conjunction with the drawings and specific embodiments.

Fig. 1 is the circuit theory schematic diagram of current-mode DC-DC voltage boosting converter

Fig. 2 is the circuit theory schematic diagram of current-mode dc-dc boost converter.

Fig. 3 is the circuit theory schematic diagram of the sawtooth waveforms generating means of the adaptive equalization that is used to boost provided by the invention among Fig. 1.

Fig. 4 is the circuit theory schematic diagram that is used for the sawtooth waveforms generating means of step-down adaptive equalization provided by the invention among Fig. 2.

Fig. 5 is the multistage RC low-pass filter circuit principle schematic of single order RC low pass filter among alternative Fig. 3 or Fig. 4.

Fig. 6 is the Active RC low-pass filter circuit principle schematic of single order RC low pass filter among alternative Fig. 3 or Fig. 4.

Fig. 7 is a voltage to current converter circuit theory schematic diagram among the another kind of Fig. 1 of voltage to current converter among alternative Fig. 3 or Fig. 4.

Embodiment

The present invention is that to the core contribution of DC-DC converter the sawtooth waveforms generating means that compensates usefulness only uses the VIN or the VOUT that can directly obtain, and at first, according to table two its operation principle is described:

See Table two, only need to measure the value of D and one of them value among VIN, the VOUT and converter chip all can directly obtain a kind of voltage, therefore another value that not directly obtains among VIN, the VOUT can be obtained by the relation in the table two, can obtain needed all feedback signals of adaptive equalization thereby need not increase terminal pin.

Below, the saw-toothed wave generator that booster converter () and buck converter (two) inside are used for adaptive equalization illustrates its principle and the concrete circuit of implementing respectively:

(1) booster converter: VOUT is commonly used to the converter chip power supply, and VIN then is free of attachment to converter chip.Therefore, VOUT is known, VIN the unknown, and we will obtain VIN by detecting VOUT and D.

M with booster converter in the table one ₂In value substitution formula [2], and according to the fixed relationship of VIN, VOUT and D in the table two, acquisition formula [4]:

$m_a=0.5{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C20051003707000132.png"\; state="\{\{state\}\}">m</figure-callout>}}_2=0.5(-\frac{\mathrm{VIN}-\mathrm{VOUT}}{L})=\frac{\mathrm{VOUT}-\mathrm{VIN}}{2L}=\frac{D\&CenterDot;\mathrm{VOUT}}{2L}---\left[4\right]$

Principle according to above-mentioned table two description, its saw-toothed wave generator specific implementation circuit as shown in Figure 3, this moment, VOUT was set to converter chip 1 power supply, clock CLK is by behind the low pass filter 3, because the high level of clock is VOUT, therefore, the output of filter will be the product of clock duty cycle and VOUT, i.e. D*VOUT; Give capacitor C r charging by voltage to current converter 4 again, because the comparator of voltage to current converter 4 inputs+and-the end input voltage is equal, then the electric current on the resistance R r is D*VOUT/Rr, gives capacitor C r charging behind this current mirror, and capacitor C r output voltage is changed to:

$\mathrm{\&Delta;Vramp}=\frac{D\&CenterDot;\mathrm{VOUT}}{\mathrm{Rr}\&CenterDot;\mathrm{Cr}}\mathrm{\&Delta;t}$

The i.e. variation slope m of this output voltage _a' be formula [5 ']:

${m_a}^{\&prime;}=\frac{\mathrm{\&Delta;Vramp}}{\mathrm{\&Delta;t}}=\frac{D\&CenterDot;\mathrm{VOUT}}{\mathrm{Rr}\&CenterDot;\mathrm{Cr}}---[5\text{'}]$

The variation slope of its equivalent output current is:

$m_a=\frac{{m_a}^{\&prime;}}{A\&CenterDot;\mathrm{Rs}}=\frac{D\&CenterDot;\mathrm{VOUT}}{A\&CenterDot;\mathrm{Rs}\&CenterDot;\mathrm{Rr}\&CenterDot;\mathrm{Cr}}---\left[5\right]$

The value modus ponens [6] of Rr and Cr wherein:

A·Rs·Rr·Cr＝2L -------------[6]

The variation slope of this saw-toothed wave generator equivalence output current satisfies the requirement of formula [4].

Wherein, low pass filter 3 is an integrated circuit unit, is single order RC passive low ventilating filter; Voltage to current converter 4 adds input amplifier for the image current source circuit, and this image current source circuit adopts 2 field effect transistor; Major part of the present invention is at low pass filter 3, and it realizes that need not increase terminal pin can obtain needed all feedback signals of adaptive equalization.In addition, adopt the CLK signal among the code book embodiment that control capacitance Cr discharges and recharges, also do not get rid of as adopting the signal of oscillator output among Fig. 1.

(2) buck converter: to buck converter, VIN is commonly used to the converter chip power supply, and VOUT then is free of attachment to converter chip.Therefore, VIN is known, and VOUT is unknown, and we will obtain VOUT by detecting VIN and D.

M with buck converter in the table one ₂In value substitution formula [2], and according to the fixed relationship of VIN, VOUT and D in the table two, acquisition formula [7]:

$m_a=0.5{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="C20051003707000132.png"\; state="\{\{state\}\}">m</figure-callout>}}_2=0.5\left(\frac{\mathrm{VOUT}}{L}\right)=\frac{\mathrm{VOUT}}{2L}=\frac{D\&CenterDot;\mathrm{VIN}}{2L}---\left[7\right]$

Principle according to above-mentioned table two description, its saw-toothed wave generator specific implementation circuit as shown in Figure 4, this moment, VIN was set to converter chip 1 power supply, clock CLK is by behind the low pass filter 3, because the high level of clock is VIN, therefore, the output of filter will be the product of clock duty cycle and VIN, i.e. D*VIN; Give capacitor C r charging by voltage to current converter 4 again, because the comparator of voltage to current converter 4 inputs+and-the end input voltage is equal, then the electric current on the resistance R r is D*VIN/Rr, gives capacitor C r charging behind this current mirror, and capacitor C r output voltage is changed to:

$\mathrm{\&Delta;Vramp}=\frac{D\&CenterDot;\mathrm{VIN}}{\mathrm{Rr}\&CenterDot;\mathrm{Cr}}\mathrm{\&Delta;t}$

The i.e. variation slope m of this output voltage _a' be formula [8 ']:

${m_a}^{\&prime;}=\frac{\mathrm{\&Delta;Vramp}}{\mathrm{\&Delta;t}}=\frac{D\&CenterDot;\mathrm{VIN}}{\mathrm{Rr}\&CenterDot;\mathrm{Cr}}---[8\text{'}]$

The variation slope of its equivalent output current is:

$m_a=\frac{{m_a}^{\&prime;}}{A\&CenterDot;\mathrm{Rs}}=\frac{D\&CenterDot;\mathrm{VIN}}{A\&CenterDot;\mathrm{Rs}\&CenterDot;\mathrm{Rr}\&CenterDot;\mathrm{Cr}}---\left[8\right]$

The value modus ponens [9] of Rr and Cr wherein:

A·Rs·Rr·Cr＝2L -------------[9]

The variation slope of this saw-toothed wave generator output voltage satisfies the requirement of formula [7].

Wherein, low pass filter 3 is an integrated circuit unit, is single order RC passive low ventilating filter; Voltage to current converter 4 adds input amplifier for the image current source circuit, and this image current source circuit adopts 2 field effect transistor; Major part of the present invention is at low pass filter 3, and it realizes that need not increase terminal pin can obtain needed all feedback signals of adaptive equalization.In addition, adopt the CLK signal among the code book embodiment that control capacitance Cr discharges and recharges, also do not get rid of as adopting the signal of oscillator output among Fig. 2.

In present technique field those of ordinary skill understanding scope, saw-toothed wave generator of the present invention can be done many distortion, wherein:

As Fig. 5, low pass filter 3 adopts multistage RC passive low ventilating filter.

As Fig. 6, low pass filter 3 adopts the Active RC low pass filter, and this mode realizes that simply cost is lower.The Active RC low pass filter can be single order or multistage, also can be ACTIVE C LOW-PASS FILTERS.

As Fig. 7, the mirror current source circuit part in the voltage-current converter 4 adopts 3 field effect transistor.

The above only is preferred embodiment of the present invention, and all equalizations of being done according to claim scope of the present invention change and modify, and all should belong to the covering scope of claim of the present invention.

Claims (10)

1, a kind of sawtooth waveforms generating means is integrated in the current mode PWM DC-DC converter chip (1,2), it is characterized in that, comprising:

Low pass filter (3), input connect the clock signal (CLK) of the inner dc-dc conversion switching circuit of this converter chip of control;

Voltage to current converter (4), input is connected with the output of described low pass filter;

Controlled switch and electric capacity (Cr) in parallel, a ground connection, the other end connects the output of described voltage to current converter, and described controlled switch is pressed certain hour frequency closure/disconnection.

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 2, described converter chip is the chip (1) that boosts, the power supply of this chip that boosts is provided by its output voltage (VOUT).

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 3, described converter chip is step-down chip (2), the power supply of this step-down chip is provided by its input voltage (VIN).

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 4, described low pass filter (3) is the above RC passive low ventilating filter of single order or single order.

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 5, described low pass filter (3) is the above active low-pass filter of single order or single order.

According to the described sawtooth waveforms generating means of claim 5, it is characterized in that 6, described active low-pass filter (3) is RC or C active low-pass filter.

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 7, described voltage to current converter (4) is controlled mirror current source.

According to the described sawtooth waveforms generating means of claim 7, it is characterized in that 8, it is one amplifier that the input of described controlled mirror current source is provided with the voltage multiple.

According to the described sawtooth waveforms generating means of claim 1, it is characterized in that 9, the control end of described controlled switch connects the clock signal (CLK) of the inner dc-dc conversion switching circuit of described converter chip.

10, according to the described sawtooth waveforms generating means of claim 1, it is characterized in that the control end of described controlled switch connects the output of described converter chip internal oscillator.

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