CN101165984A - Circuit for producing retarding window - Google Patents

Abstract

This invention relates to a circuit for generating a retarding window including a general comparator, a switch tube, a reference voltage and a resistor branch composed of resistor R3 and resistor R4 in series, the same phase input end of the comparator is connected with the reference voltage, the inverse input end is connected with the resistor branch and input current passes through the resistor branch and the inverse input end of the comparator, the source and drain of the switch tube is bridge-connected to the two ends of R3 and the drain is connected to the inverse input end of the comparator, the grid of the switch tube is connected to the output of the comparator, and when input current works normally, said reference voltage is set larger than the voltage of the inverse input end of the comparator. This invention utilizes gating of a switch tube to two resistors R3 and R4 to generate a retarding window and adjust it accurately.

Description

A kind of circuit that produces retarding window

Technical field

The present invention relates to a kind of circuit that produces retarding window, this circuit is applicable in the protective circuits such as excess temperature, overcurrent.

Background technology

Portable electric appts (as mobile phone, PDA, MP3 etc.) is mainly powered through low-voltage drop linear voltage regulator (LDO) and switching regulator direct current regulator (DCDC) by lithium battery at present, all adopts power tube in these power supply changeover devices.The quality index of power supply changeover device should be to be first principle with fail safe, reliability.Satisfy in the electrical technology index under the condition of normal instructions for use, under adverse circumstances and catastrophic failure situation, work safely and reliably for making power supply, must design kinds of protect circuit, such as protective circuits such as the soft start of anti-surge, under-voltage, excess temperature, overcurrents.For example, along with the continuous increase of SOC chip integrated functionality and scale and the fast development of portable use, the function of chip is more and more, and power consumption is increasing, causes the temperature of chip operation also more and more higher.But the too high temperature of chip can reduce its reliability greatly, even directly causes chip to produce hot stall.So thermal-shutdown circuit seems for power management chip and is even more important.Thermal-shutdown circuit is exactly to continue the detection chip temperature, establishes the upper limit (T if temperature surpasses _Off), will produce cut-off signals, if temperature drops to permissible value (T _On), will produce start signal, operation principle is as shown in Figure 1.Obviously, in order to prevent thermal oscillation, T _OffAnd T _OnCertain retarding window should be set, and all be to adopt hysteresis comparator to produce a temperature hysteresis window at present.

Fig. 2 a is a general comparator circuit symbol, and this comparator can compare two input analog signals and produce the circuit of a binary system output thus.Fig. 2 b is the curve of output of this comparator, and when the difference of positive and negative input is timing, comparator is output as high level (V _OH); When negative, comparator is output as low level (V _OL).And Fig. 3 a is a hysteresis comparator, and its input threshold value is the function of input (or output) level.Especially export and can change through threshold value when input, simultaneously, the input threshold value also can decrease, so must get back to a threshold value before the change state again in the output of comparator.More than changing to be presented in the curve of output shown in Fig. 3 b clearly: input begins and to when changing from negative value, exports constantly, reaches forward breakover point V up to input _TRP+The time, the output of comparator just begins to change; In case output uprises, actual breakover point is changed; When importing when the negative value direction reduces, export constant; Reach negative sense breakover point V up to input _TRP-The time, the output of comparator just begins to change.Regulate the dimension scale of the relative M6 of load pipe M3 and M7 in the hysteresis comparator circuit shown in Figure 3, just can regulate the size that obtains retarding window, be i.e. V among Fig. 3 (b) with M4 _TRP+-V _TRP-Size.

Fig. 4 is that an at present very common hysteresis comparator that utilizes produces temperature hysteresis window thermal-shutdown circuit.Branch road 1-3 is band-gap reference (Bandgap) circuit, and VREF is the temperature independent voltage that this circuit obtains, I _PTATIt is the electric current that is directly proportional with temperature that this circuit obtains.If two bipolar transistors are under unequal current density, the difference of their base-emitter voltage just is directly proportional with absolute temperature so, $I_{\mathrm{PTAT}}=\frac{1}{R_1}{V}_T\ln n,$ Wherein n represents the ratio of two bipolar transistor emitter area, V _TLnn represents the difference of base-emitter voltage of two PNP pipes of 1 branch road and 2 branch roads, is positive temperature coefficient.This electric current I that is directly proportional with temperature of MP1 and MP2 mirror image _PTAT

VA＝I _PTAT*R ₃(1)

VB＝V _Be(2)

Comparator input voltage VA is a positive temperature coefficient voltage as can be seen from expression formula (1), (2), and VB is a negative temperature coefficient voltage.VB＞VA under the normal use temperature conditions, the output VOUT of hysteresis comparator is a high potential; Along with the rising of temperature, VB diminishes, and it is big that VA becomes, up to some temperature threshold value T _Off, VB＜VA, the output VOUT of hysteresis comparator is an electronegative potential.This current potential has characterized circuit and whether has been in over-temperature condition.Owing to adopted hysteresis comparator, therefore produce a temperature hysteresis window, Fig. 4 circuit comparator output potential with the relation of temperature just as shown in Figure 1, T wherein _Off-T _OnIt is exactly the temperature hysteresis window.

As seen from the above analysis; traditional protective circuit all utilizes hysteresis comparator to produce retarding window; and the place one's entire reliance upon structure of hysteresis comparator of the retarding window that hysteresis comparator produces; promptly rely on the adjusting of hysteresis comparator load pipe dimension scale; and load pipe dimension scale is difficult for regulated at will, and the retarding window that causes traditional hysteresis comparator to produce is difficult for regulating.Therefore existing overheat protector or the current foldback circuit that utilizes hysteresis comparator to form all has the defective that retarding window is difficult for adjusting.

Summary of the invention

Technical problem to be solved by this invention is: a kind of circuit of new generation retarding window is provided, and this circuit has brought retarding window in design flexibly and the advantage of being convenient to regulate.

The present invention solves the problems of the technologies described above the technical scheme that is adopted to be:

A kind of circuit that produces retarding window comprises a general comparator, a switching tube, a reference voltage, and the resistance branch that is composed in series by first resistance and second resistance; The in-phase input end of described comparator connects reference voltage, and its inverting input connects described resistance branch, the flow through inverting input of resistance branch and comparator of input current; The source of described switching tube, drain electrode are connected across the described first resistance two ends, and drain electrode connects the inverting input of comparator, the output of the grid connection comparator of described switching tube; When input current during, described reference voltage is set greater than described comparator inverting input voltage in normal operating conditions.

The circuit of described generation retarding window, wherein: described switching tube adopts NPN type field effect transistor.

Produce the circuit of retarding window, wherein: when this circuit is used in the current foldback circuit, the detection electric current of described input current for being directly proportional with load current; When this circuit is used in the thermal-shutdown circuit, the positive temperature coefficient electric current of described input current for raising and increase with temperature, and the negative temperature coefficient voltage of described reference voltage for raising and diminish with temperature is set.

The circuit of described generation retarding window, wherein: described reference voltage is produced by the transistorized BE knot of a PNP.

A kind of circuit that produces retarding window comprises a general comparator, a switching tube, a reference voltage, an inverter and the resistance branch that is composed in series by first resistance and second resistance; The inverting input of described comparator connects reference voltage, and its in-phase input end connects described resistance branch, the flow through in-phase input end of resistance branch and comparator of input current, and the output of described comparator connects the input of inverter; The source of described switching tube, drain electrode are connected across the described first resistance two ends, and drain electrode connects the inverting input of comparator, the output of the grid connection inverter of described switching tube; When input current during, described reference voltage is set greater than described comparator in-phase input end voltage in normal operating conditions.

The circuit of described generation retarding window, wherein: described switching tube adopts NPN type field effect transistor.

Beneficial effect of the present invention is: circuit of the present invention no longer needs the hysteresis comparator in the traditional scheme, the adjusting of retarding window also is no longer dependent on the adjusting of hysteresis comparator load pipe ratio, only need to regulate the size of resistance R 3 and R4, just can be easy to and regulate more accurately retarding window, this has brought very big design flexibility in design.And this circuit can be realized on standard CMOS process, the circuit low cost of manufacture.

Description of drawings

Fig. 1 is a thermal-shutdown circuit operation principle schematic diagram;

Fig. 2 a is the general comparator circuit symbol;

Fig. 2 b is the curve of output of general comparator;

Fig. 3 a is the hysteresis comparator circuit schematic diagram;

Fig. 3 b is the hysteresis comparator transmission curve;

Fig. 4 utilizes hysteresis comparator to produce the thermal-shutdown circuit of temperature hysteresis window;

Fig. 5 produces the circuit of retarding window for the present invention;

Fig. 6 produces the thermal-shutdown circuit of retarding window circuit for adopting the present invention;

Fig. 7 is the temperature curve of thermal-shutdown circuit of the present invention;

Fig. 8 is the simulated temperature curve of the thermal-shutdown circuit of employing circuit of the present invention;

Fig. 9 is the current foldback circuit of prior art;

Figure 10 is applied to the schematic diagram of current foldback circuit for the present invention;

Figure 11 is second kind of circuit that produces retarding window of the present invention.

Embodiment

With embodiment the present invention is described in further detail with reference to the accompanying drawings below:

The circuit that the present invention produces retarding window is to utilize resistance and switching tube to produce one to be convenient to regulate and the retarding window of flexible design.This circuit comprises a general comparator, a switching tube MS as shown in Figure 5, and switching tube MS adopts NPN type field effect transistor, a reference voltage V _REF, and the resistance branch that is composed in series by first resistance R 3 and second resistance R 4; The in-phase input end of comparator connects reference voltage V _REF, its inverting input connects the resistance branch that R3, R4 form; The source of switching tube, drain electrode are connected across resistance R 3 two ends, and drain electrode connects the inverting input of comparator, the output of the grid connection comparator of switching tube.The input current I of node A flows through _InBe a variable, in thermal-shutdown circuit, input current I _InBe the electric current that is directly proportional with temperature, in current foldback circuit, input current I _InBe the detection electric current that is directly proportional with load current, and as input current I _InWhen normal operating conditions, reference voltage V is set _REFGreater than comparator inverting input voltage, promptly the in-phase input end voltage of comparator is greater than its inverting input voltage, and this moment, comparator was exported V _OUTBe high potential, switching tube MS conducting, resistance R 3 is equivalent to the bypass by switching tube MS; When excess temperature or overload cause input current I _InWhen rising to first critical value, the inverting input voltage of comparator is greater than its normal phase input end voltage, and this moment, comparator reversed, and it exports V _OUTBe electronegative potential, switching tube MS by, resistance R 3 no longer by switching tube MS bypass and and the R4 series connection.In order clearly to analyze circuit of the present invention how under the prerequisite that does not increase power consumption; utilize the switching tube gating of R3, two resistance of R4 is produced retarding window and realize the accurate adjusting of retarding window; below respectively with this circuit application in thermal-shutdown circuit and current foldback circuit, detailed in addition narration.

Thermal-shutdown circuit as shown in Figure 6, branch road 1-3 is the same with Fig. 4 prior art scheme.Utilize band-gap reference (Bandgap) circuit to produce a temperature independent reference voltage V REF, MP1 and MP2 mirror image obtain an input current I who is directly proportional with temperature _PTATComparator among the branch road 4-5 no longer needs hysteresis comparator and adopts and do not have sluggish general comparator replacement.Because input current I _PTATBe positive temperature coefficient, comparator input voltage VA is a positive temperature coefficient voltage, and in order to improve the sensitiveness of thermal-shutdown circuit, reference voltage VB is a negative temperature coefficient voltage that is produced by the transistorized BE knot of PNP.VB＞VA in the normal working temperature scope, comparator output V _OUTBe high potential, switching tube MS conducting.We design the conducting resistance r of switching tube MS _Ds＜＜R ₃, thereby in the normal working temperature scope, resistance R 3 is by switching tube MS bypass, simultaneously the conducting resistance r of switching tube MS _Ds＜＜R ₄So, have:

VA ₁＝I _PTAT1*R ₄(3)

VB ₁＝V _EB1(4)

VB in the normal working temperature scope ₁＞VA ₁Along with temperature rises, the I of positive temperature coefficient _PTATRising causes voltage VA to rise, and the voltage VB of negative temperature coefficient descends, when rising to the first critical temperature T _OffThe time, VB ₁＜VA ₁, comparator upset this moment, output voltage V _OUTBe electronegative potential, this characterization circuit is in the excess temperature situation.Comparator output this moment V _OUTClose for electronegative potential causes switching tube MS, resistance R 3 is no longer connected with R4 by switching tube MS bypass.Along with system closing, temperature descends, at this moment

VA ₂＝I _PTAT2*(R ₃+R ₄)(5)

VB ₂＝V _EB2(6)

When dropping to the second critical temperature T _OnThe time, VB ₂＞VA ₂, comparator upset, output V _OUTBe high potential, illustrative system returns to the temperature of a safety, can restart.Observe the temperature curve of thermal-shutdown circuit of the present invention shown in Figure 7, find that the state owing to switching tube MS had played a decisive action to voltage VA when temperature rose and temperature descends.In the temperature uphill process, MS is in conducting state always, and first critical temperature in the comparator upset has:

$I_{\mathrm{<figure-callout\; id="1"\; label="PTAT"\; filenames="A20061006325700132.png"\; state="\{\{state\}\}">PTAT</figure-callout>}1}*R_4=V_{\mathrm{EB},T_{\mathrm{off}}}$ Promptly ${\mathrm{<figure-callout\; id="1"\; label="I\; PTAT"\; filenames="A20061006325700132.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{PTAT}}=V_{\mathrm{BE},T_{\mathrm{off}}}/R_4---\left(7\right)$

In the temperature decline process, and MS is in closed condition always, and second critical temperature in the comparator upset has:

$I_{\mathrm{<figure-callout\; id="2"\; label="PTAT"\; filenames="A20061006325700142.png,A20061006325700151.png"\; state="\{\{state\}\}">PTAT</figure-callout>}2}*(R_3+R_4)=V_{\mathrm{EB},T_{\mathrm{on}}}$ Promptly ${\mathrm{<figure-callout\; id="2"\; label="I\; PTAT"\; filenames="A20061006325700142.png,A20061006325700151.png"\; state="\{\{state\}\}">I</figure-callout>}}_{\mathrm{PTAT}}=V_{\mathrm{EB},T_{\mathrm{on}}}/(R_3+R_4)---\left(8\right)$

We carry out following analysis according to formula (7) and (8): suppose T _Off≤ T _OnSet up, because I _PTATWith temperature be the relation of positive temperature coefficient, so I is arranged _PTAT1≤ I _PTAT2And V _EBWith temperature be the relation of negative temperature coefficient, so have $V_{\mathrm{EB},T_{\mathrm{off}}}\&GreaterEqual;V_{\mathrm{EB},T_{\mathrm{on}}},$ Substitution (7) and (8) formula obtain $V_{\mathrm{EB},T_{\mathrm{off}}}/R_4\&GreaterEqual;V_{\mathrm{EB},T_{\mathrm{on}}}/(R_3+R_4),$ Be I _PTAT1〉=I _PTAT2The hypothesis of conclusion and beginning is inconsistent, so T is arranged _Off＞T _On, promptly produced size and be T _Off-T _OnThe temperature hysteresis window.

By above analysis; when the temperature hysteresis window design of thermal-shutdown circuit; no longer need the hysteresis comparator in the traditional scheme; the adjusting of temperature hysteresis window is no longer dependent on the adjusting of hysteresis comparator load pipe ratio; only need to regulate the size of resistance R 3 and R4; can be easy to and regulate more accurately the temperature hysteresis window, this has brought very big design flexibility in design.The temperature curve of this circuit working shown in Figure 8 is one and realizes example.Branch road 1-5 quiescent current at room temperature is 2 microamperes (uA), R3=20K ohm, and R4=100K ohm, the temperature hysteresis window that obtains is 20 ℃.Under the certain situation of the quiescent current of every branch road, by regulating the size of R3 and R4, the size that can regulate retarding window flexibly.

Circuit of the present invention can be used in the current foldback circuit equally, is used for producing the electric current retarding window.Fig. 9 is the typical current foldback circuit of prior art.V _REFBe reference voltage, I _SenceBe output load current I _LOADMirror image detect current value, observe the mirror image proportionate relationship:

I _LOAD/I _sense＝K(9)

By comparison reference voltage V _REFAnd I _Sence* R ₄Size judges whether that load current is excessive.When the output load current value is in normal range (NR), V _REF＞I _Sence* R ₄, comparator output V _OUTBe high potential; As output load current increase, then I _SenceIncrease, up to the critical point of output load current, V _REF＜I _Sence* R ₄, then comparator is exported V _OUTBecome electronegative potential, this characterization system be in over-current state.In order to prevent current oscillation, adopted hysteresis comparator to produce an electric current retarding window in traditional current foldback circuit, load pipe dimension scale obtains its electric current retarding window in the hysteresis comparator by regulating.

Figure 10 is that this programme is applied in the current foldback circuit.It still utilizes resistor network and switching tube to produce the electric current retarding window.System power load I _LOADIn the time of in normal range (NR), reference voltage V _REF＞I _Sence* R ₄, comparator output V _OUTBe high potential, switching tube MS conducting; Current loading rises to the first critical value I _{LOAD, OFF}The time,

V _REF＝I _sence，off*R ₄(10)

Current loading is greater than the first critical value I _{LOAD, OFF}The time, comparator output V _OUTBe electronegative potential, this characterization system is in over-current state, and after this switching tube MS closes, V _REF＜I _Sence* (R ₃+ R ₄); When current loading begins to drop to the second critical value I _{LOAD, ON}The time,

V _REF＝I _sence，on*(R ₃+R ₄)(11)

Comparator output V _OUTRevert to high potential again, characterization system is in the normal current loading, switching tube MS conducting after this, V _REF＞I _Sence* R ₄The retarding window that we can obtain electric current according to above analysis is:

I _LOAD，OFF-I _LOAD，ON＝(I _sence，off-I _sence，on)*K

According to (10) and (11), the retarding window of electric current is: $(\frac{1}{R_4}-\frac{1}{R_3+R_4})*\mathrm{VREF}*K---\left(12\right)$

By regulating the size of resistance R 3 and R4, can very accurately obtain the electric current retarding window easily, make the design of retarding window not rely on hysteresis comparator.

Circuit of the present invention also has improvement project as shown in figure 11, what improvement project was different with the basic scheme shown in the figure is, the inverting input of comparator connects reference voltage, in-phase input end connects described resistance branch, the output of comparator has increased a reverser simultaneously, and the grid of switching tube MS connects the output of inverter.When input current during in normal operating conditions, reference voltage is set greater than comparator in-phase input end voltage, this moment, comparator was output as electronegative potential, inverter is output as high potential, switching tube MS is in conducting state, its operation principle is identical with basic scheme, is the accurate adjusting that utilizes the switching tube gating of R3, two resistance of R4 is produced retarding window and realize retarding window equally, does not repeat them here.

By as seen above-mentioned, circuit structure of the present invention is simple, under the prerequisite that does not increase any power consumption, utilized resistor network and a switching tube to realize retarding window, make the use that to break away from hysteresis comparator in the occasion that needs retarding window, and the present invention can make the easier more accurate adjusting of retarding window size; This circuit can be realized on standard CMOS process, the circuit low cost of manufacture.The excess temperature, current foldback circuit that circuit of the present invention is specially adapted to LDO, Charger or DC-DC also can be applied in the occasion that other needs retarding window simultaneously in using.

Should be understood that; the circuit of generation retarding window of the present invention; above-mentioned description at preferred embodiment is too concrete; can not therefore be interpreted as restriction to scope of patent protection of the present invention; for those of ordinary skills; can be equal to replacement or change according to technical scheme of the present invention and inventive concept thereof, and all these changes or replacement all should belong to the protection range of the appended claim of the present invention.

Claims (6)

1. circuit that produces retarding window is characterized in that: comprise a general comparator, a switching tube, a reference voltage, and the resistance branch that is composed in series by first resistance and second resistance; The in-phase input end of described comparator connects reference voltage, and its inverting input connects described resistance branch, the flow through inverting input of resistance branch and comparator of input current; The source of described switching tube, drain electrode are connected across the described first resistance two ends, and drain electrode connects the inverting input of comparator, the output of the grid connection comparator of described switching tube; When input current during, described reference voltage is set greater than described comparator inverting input voltage in normal operating conditions.

2. the circuit of generation retarding window according to claim 1 is characterized in that: described switching tube adopts NPN type field effect transistor.

3. the circuit of generation retarding window according to claim 2 is characterized in that: when this circuit is used in the current foldback circuit, and the detection electric current of described input current for being directly proportional with load current; When this circuit is used in the thermal-shutdown circuit, the positive temperature coefficient electric current of described input current for raising and increase with temperature, and the negative temperature coefficient voltage of described reference voltage for raising and diminish with temperature is set.

4. the circuit of generation retarding window according to claim 3 is characterized in that: described reference voltage is produced by the transistorized BE knot of a PNP.

5. a circuit that produces retarding window is characterized in that: comprise a general comparator, a switching tube, a reference voltage, an inverter and the resistance branch that is composed in series by first resistance and second resistance; The inverting input of described comparator connects reference voltage, and its in-phase input end connects described resistance branch, the flow through in-phase input end of resistance branch and comparator of input current, and the output of described comparator connects the input of inverter; The source of described switching tube, drain electrode are connected across the described first resistance two ends, and drain electrode connects the inverting input of comparator, the output of the grid connection inverter of described switching tube; When input current during, described reference voltage is set greater than described comparator in-phase input end voltage in normal operating conditions.

6. the circuit of generation retarding window according to claim 5 is characterized in that: described switching tube adopts NPN type field effect transistor.

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