CN101165983B - Current limiting short circuit protection circuit - Google Patents

Abstract

This invention discloses a protection circuit of limit short circuit including field effect transistors M0, M1, M2, M3, M4, power valves MP1 and MP2 and resistor R3, in which, a current mirror made upof M0, M1 and M2 is in the equal proportion to an image circuit and the sources of M0, M1 and M2 are connected to the earth, the drains of M1 and M2 are connected with the drains of M3 and M4, and M3and M4 form the image circuit, one end of R3 is connected with the sources of M3 and MP1, the other end is connected with the sources of M4 and MP2.

Description

A kind of current limiting short circuit protection circuit

Technical field

The present invention relates generally to the power management integrated circuit field, especially is applicable to the current limiting short circuit protection circuit of power management integrated circuit.

Background technology

Current, 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.All adopted 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.Yet power management chips such as DC-DC, LDO may be led because of application error or other contingency and put the output short circuit when being used, and will produce a very big electric current like this, enough burn chip.So; 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, must design the kinds of protect circuit for making power supply; such as the soft start of anti-surge, under-voltage, overheated, cross protective circuits such as flow short-circuit, phase shortage.

At present, relatively Chang Yong current limiting short circuit protection circuit mainly is the size of continuous detecting load current, and is very big unusual if detected value occurs, and system just thinks and overcurrent/short circuit produces overcurrent/short circuit shutdown signal.Simply tell about several frequently seen typical existing current limiting short circuit protection circuit below:

A. adopt the precision resistance scheme:

As shown in Figure 1, this scheme uses a plug-in precision resistance Rsense to connect with power tube MP1, comes the electric current of detection power pipe by the voltage of measuring the precision resistance two ends.Vgate is from the control signal of chip to power tube among the figure, and VCC is the input power supply, and VSS is simulation ground.Its operation principle is as follows: resistance R sense is a precision resistance that resistance is very little, and 0.2 Ω for example flows through resistance R sense during to power tube MP1 when electric current, and the pressure drop at the Rsense two ends is:

V _Rsense＝I _Rsense*Rsense (1)

Because the empty fugitive of amplifier answered, its input terminal voltage keeps equating (get R1 in the circuit and equal R2), thereby the voltage at R2 two ends equals V _RsenseThereby the electric current of the R2 that can obtain flowing through is directly proportional with Isense, can obtain the voltage Vsense that is directly proportional with Isense equally, and its size is:

$\mathrm{Vsense}=\frac{R3*\mathrm{Rsense}*\mathrm{Isense}}{R2}---\left(2\right)$

And the relative scale of R3/R2 is to do accurately than being easier in integrated circuit.The Vsense that obtains from above analysis has realized the detection to the power tube output current, thereby can compare by Vsense and a reference voltage V REF and do current limliting/short-circuit protection circuit.As Fig. 2, general COMP is a hysteresis comparator, and the high-low level of COMP_OUT output is used for judging whether overcurrent/short circuit.

B. adopt power tube self internal resistance scheme

Similar with top method, as shown in Figure 3, directly use the resistance of power tube self to detect its electric current.Suppose that power tube resistance is R _MP1, resistance R 1 equals R2, then can obtain:

$\mathrm{Vsense}=\frac{R3*R_{\mathrm{<figure-callout\; id="1"\; label="MP"\; filenames="H200610063149XE00013.png,H200610063149XE00031.png"\; state="\{\{state\}\}">MP</figure-callout>}1}*\mathrm{Isense}}{R2}---\left(3\right)$

${\mathrm{<figure-callout\; id="1"\; label="R\; MP"\; filenames="H200610063149XE00013.png,H200610063149XE00031.png"\; state="\{\{state\}\}">R</figure-callout>}}_{\mathrm{MP}}=\frac{1}{{\mathrm{\&mu;}}_n{C}_{\mathrm{ox}}\frac{L}{W}(V_{\mathrm{GS}}-V_{\mathrm{TH}})}---\left(4\right)$

The internal resistance of power tube MP1 changes with supply voltage or its gate source voltage, as following formula (4), thereby is not very accurate by the detected electric current of this scheme.

C. adopt tubule scheme with the power tube coupling

As shown in Figure 4, this circuit adopts the tubule MP2 that mates with power tube MP1 to detect electric current.Vgate is the output of error amplifier in the circuit, and VFB is the voltage that LDO feeds back to error amplifier.Get:

$\frac{W}{L_{\mathrm{MP}2}}=\frac{1}{N}\frac{W}{L_{\mathrm{MP}1}}---\left(5\right)$

Because the clamping action of amplifier, voltage VA equals VB, so can obtain:

$I_{\mathrm{MP}2}=\frac{1}{N}{I}_{\mathrm{MP}1}---\left(6\right)$

I _sen＝I _MP2 (7)

V _sense＝I _sen*R ₃ (8)

By above analysis; can obtain the voltage Vsence that is directly proportional with power tube MP1 electric current; thereby it can be used for doing the monitoring side of current limliting or short-circuit protection circuit; compare with a bandgap voltage reference again; just can form complete current limliting or short-circuit protection circuit; the scheme of the ratio of precision precision resistance of this electric circuit inspection electric current is low, and its shortcoming is the structure more complicated, and power consumption is bigger.

The basic thought of existing above several schemes is exactly to obtain a monitoring voltage Vsence that can monitor the output current size earlier, itself and a reference voltage is made comparisons to judge whether overcurrent/short circuit again.Such scheme is owing to need amplifier, a hysteresis comparator and a reference voltage V REF etc., circuit generally to seem complicated, and power consumption makes too greatly that generally current efficiency reduces greatly; And circuit is (as LDO; Charger etc.) when operate as normal; this current limliting/short-circuit protection circuit is in continuous detecting operating state relatively forever; wasted power consumption greatly; especially circuit (as LDO) load current be 0 or load current hour, this too much power consumption will reduce the efficient of system greatly.And the A scheme needs plug-in one the integrated precision resistance that is difficult to especially, has increased system cost, has reduced the efficient of system.

Summary of the invention

The object of the present invention is to provide a kind of current limiting short circuit protection circuit, this circuit low-power consumption is applicable to power management integrated circuit.

In order to solve the problems of the technologies described above; the technical solution used in the present invention comprises a kind of current limiting short circuit protection circuit; this circuit comprises first field effect transistor (M0); second field effect transistor (M1); the 3rd field effect transistor (M2); the 4th field effect transistor (M3); the 5th field effect transistor (M4); first power tube (MP1); second power tube (MP2) and first resistance (R3); described first field effect transistor (M0); second field effect transistor (M1) and the 3rd field effect transistor (M2) are formed current mirror equal proportion mirror image circuit; the source electrode of described first field effect transistor (M0); the source electrode of second field effect transistor (M1) all is connected with ground with the source electrode of the 3rd field effect transistor (M2); the drain electrode of described second field effect transistor (M1) links to each other with the drain electrode of described the 4th field effect transistor (M3); the drain electrode of described the 3rd field effect transistor (M2) links to each other with the drain electrode of described the 5th field effect transistor (M4); described the 4th field effect transistor (M3) and the 5th field effect transistor (M4) are formed mirror image circuit; one end of described first resistance (R3) links to each other with the source electrode of described the 4th field effect transistor (M3) and the source electrode of described first power tube (MP1), and the other end of described first resistance (R3) links to each other with the source electrode of described the 5th field effect transistor (M4) and the source electrode of described second power tube (MP2).

Adopt technique scheme, in conjunction with the following embodiment that will describe in detail, beneficial technical effects of the present invention is: current limiting short circuit protection circuit of the present invention does not need plug-in precision resistance and adopts the method for dynamically self regulating, only used extra small power consumption with regard to the higher precision that gets, thereby reduced design cost, improved current efficiency, and the short circuit over-current protection circuit response speed is fast; Current limiting short circuit protection circuit of the present invention almost is in closed condition, current sinking hardly when power supply core circuit operate as normal; When overcurrent/short-circuit conditions appears in the power supply core circuit, just consume certain power consumption; The core circuit load current be 0 or load current hour, short circuit over-current protection circuit can be closed automatically.

Feature of the present invention and advantage will be elaborated in conjunction with the accompanying drawings by embodiment.

Description of drawings

Fig. 1 is the existing current limiting short circuit protection circuit figure that utilizes precision resistance to detect current scheme.

Fig. 2 produces current limliting/short-circuit protection signal schematic representation for existing C OMP.

Fig. 3 is the existing current limiting short circuit protection circuit figure that utilizes the power tube self-resistance to detect current scheme.

Fig. 4 is the existing current limiting short circuit protection circuit figure that utilizes tubule mirror image power tube to detect current scheme

Fig. 5 is the circuit diagram of current limiting short circuit protection circuit one embodiment of the present invention.

Fig. 6 is the circuit diagram of another embodiment of current limiting short circuit protection circuit of the present invention.

Embodiment

As shown in Figure 5, be the circuit diagram of current limiting short circuit protection circuit one embodiment of the present invention.The current mirror equal proportion mirror image bias current Ibias that this current limiting short circuit protection circuit adopts the pipe first field effect transistor M0, the second field effect transistor M1, the 3rd field effect transistor M2 to form; The breadth length ratio of little second power tube MP2 and the big first power tube MP1 is 1: N; The mirror image ratio of the 4th field effect transistor M3, the 5th field effect transistor M4 is K; First resistance R 3 is one hundred other polycrystalline of ohm level (poly) resistance; VCC and VSS are respectively input voltage and simulation ground, and Vo is an output, and Io is a current loading.

The first field effect transistor M0, the second field effect transistor M1, the current mirror equal proportion mirror image circuit that the 3rd field effect transistor M2 forms, the first field effect transistor M0, the second field effect transistor M1, the source electrode of the 3rd field effect transistor M2 all is connected with ground, the second field effect transistor M1, the drain electrode of the 3rd field effect transistor M2 respectively with the 4th field effect transistor M3, the drain electrode of the 5th field effect transistor M4 links to each other, the 4th field effect transistor M3, the 5th field effect transistor M4 forms mirror image circuit, one end of first resistance R 3 links to each other with the source electrode of the source electrode of the 4th field effect transistor M3 and the first power tube MP1, and the other end of first resistance R 3 links to each other with the source electrode of the 5th field effect transistor M4 and the source electrode of the second power tube MP2.

Bias current Ibias necessarily makes M4 gate voltage V _{G, M4}Be in fixed value.When this LDO was in the normal load electric current, M4 was in the linear work district, thereby the Vocp current potential is high; When load current when excessive (comprising short circuit), M4 is in the operate in saturation district, thereby the Vocp current potential becomes low.Vocp can be used as the judgement signal of overcurrent/short circuit after through two reversers.Whole overcurrent/short-circuit protection circuit consumes the quiescent current of 3*Ibias.

As shown in Figure 6, this circuit is on the basis of the above in order to reduce the further improvement that power consumption improves current efficiency.Vbias is a bias voltage, can be shared with core circuit; MP3 is the tubule of the mirror image first power tube MP1, and wide long size ratio is 1: N, and its common gate voltage Vgate controls (being error amplifier and buffer) by core circuit in LDO; The MOC pipe is that overcurrent/short-circuit protection is clamped down on pipe; The MS3 that increases on the basis of Fig. 4 is to consider from the angle of saving quiescent dissipation to MS5, they the core circuit band little/guaranteed closing of overcurrent/short-circuit protection circuit (4,5 and 6 branch road) in the zero load; MS3 is produced by 1 to 3 branch road to gate voltage Vn and the Vp of MS5.Branch road 1-3 branch road has just been realized the dynamic switch to overcurrent/protective circuit like this, to save power consumption.

Branch road 3 is because diode connects constant, the promptly certain bias current that is in work all the time, and determined MS2 gate voltage V _{G, MS2}Size.The continuous mirror image first power tube MP1 of MP3, wide long size ratio is 1: N, the core circuit band little/zero load I _MP1The time, 2 of branch roads flow through

Electric current makes MS1 be in the linear work district, makes the gate voltage of MS2 be significantly smaller than threshold voltage V simultaneously _ThThereby branch road 1 and 2 consumes bias current hardly, makes Vn be in high potential, and is in buttoned-up status by 4 to 6 branch roads of Vn and Vp control.So when core circuit is being with little/zero load I _MP1The time, protective circuit has only branch road 3 to consume bias currents, so reduced greatly system's band little/power consumption during zero load, improved current efficiency.

When the load of core circuit band increases gradually, the electric current of MP3 mirror image

Also increase, MS1 becomes the saturation region gradually by linear zone, and the gate voltage of MS2 is also greater than its threshold voltage.This moment, Vn became electronegative potential by high potential, and this transformation directly makes 4 to 6 branch roads open, and makes current limliting/short-circuit protection in running order, to reach the purpose of current limliting/short-circuit protection.

When the load of core circuit band surpassed set value (such as 400mA), M4 changed to the saturation region by being operated in linear zone, and Vocp is by higher current potential step-down.Because Vocp step-down (such as 1.5V), MOC manage conducting, the buffer of a bigger electric current (such as 2mA) inflow core circuit, voltage Vgate voltage is just clamped like this, the output current of the first power tube MP1 with regard to embedding built in certain value.So when circuit generation overcurrent/short circuit phenomenon, it is a permissible value (this value is decided by the designer) that Fig. 5 circuit comes clamped output current by clamped voltage Vgate on the one hand, and system is in abnormal working position according to Vocp current potential step-down prompt system on the one hand.

Therefore when overcurrent/short circuit took place, circuit just was in a safe condition, and can not burn chip because of big electric current.

Claims (7)

1. current limiting short circuit protection circuit; it is characterized in that: comprise first field effect transistor (M0); second field effect transistor (M1); the 3rd field effect transistor (M2); the 4th field effect transistor (M3); the 5th field effect transistor (M4); first power tube (MP1); second power tube (MP2) and first resistance (R3); described first field effect transistor (M0); second field effect transistor (M1) and the 3rd field effect transistor (M2) are formed current mirror equal proportion mirror image circuit; the source electrode of described first field effect transistor (M0); the source electrode of second field effect transistor (M1) all is connected with ground with the source electrode of the 3rd field effect transistor (M2); the drain electrode of described second field effect transistor (M1) links to each other with the drain electrode of described the 4th field effect transistor (M3); the drain electrode of described the 3rd field effect transistor (M2) links to each other with the drain electrode of described the 5th field effect transistor (M4); described the 4th field effect transistor (M3) and the 5th field effect transistor (M4) are formed mirror image circuit; one end of described first resistance (R3) links to each other with the source electrode of described the 4th field effect transistor (M3) and the source electrode of described first power tube (MP1), and the other end of described first resistance (R3) links to each other with the source electrode of described the 5th field effect transistor (M4) and the source electrode of described second power tube (MP2).

2. current limiting short circuit protection circuit as claimed in claim 1; it is characterized in that: also comprise second resistance (R1), the 3rd resistance (R2) and electric capacity (C0); described the 3rd resistance (R2) end ground connection; the other end links to each other with an end of described second resistance (R1); the other end of described second resistance (R1) is connected the drain electrode of described first power tube (MP1) and the drain electrode of described second power tube (MP2), the other end ground connection of described electric capacity (C0) jointly with the continuous back of described electric capacity (C0) end.

3. current limiting short circuit protection circuit as claimed in claim 1 or 2 is characterized in that: described the 4th field effect transistor (M3), the 5th field effect transistor (M4) mirror image ratio are K.

4. current limiting short circuit protection circuit as claimed in claim 1 or 2 is characterized in that: described first resistance (R3) is other polycrystalline resistance of hundred ohm level.

5. current limiting short circuit protection circuit as claimed in claim 1 or 2, it is characterized in that: described first field effect transistor (M0), second field effect transistor (M1), the 3rd field effect transistor (M2) current mirror equal proportion mirror image bias current are Ibias, described bias current Ibias makes the gate voltage of described the 5th field effect transistor (M4) be in fixed value, when circuit was in the normal load electric current, described the 5th field effect transistor (M4) was in the linear work district; During excessive or short circuit, described the 5th field effect transistor (M4) is in the operate in saturation district when load current.

6. current limiting short circuit protection circuit as claimed in claim 1 or 2; it is characterized in that: also comprise the 6th field effect transistor (MS3); the 7th field effect transistor (MS4); the 8th field effect transistor (MS5) and the 9th field effect transistor (MOC); the source electrode of described the 6th field effect transistor (MS3) is connected with ground; its drain electrode links to each other with the grid of described first field effect transistor (M0); the source electrode of described the 7th field effect transistor (MS4) links to each other with the drain electrode of described first field effect transistor (M0); the source electrode of described the 8th field effect transistor (MS5) links to each other with the grid of described the 9th field effect transistor (MOC); the drain electrode of described the 8th field effect transistor (MS5) connects power supply VCC, and the source electrode of described the 9th field effect transistor (MOC) connects power supply VCC.

7. current limiting short circuit protection circuit as claimed in claim 6 is characterized in that: described the 9th field effect transistor (MOC) is that overcurrent/short-circuit protection is clamped down on pipe.

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