CN116414175A - Current-limiting protection circuit for low-dropout linear voltage regulator and linear voltage regulator - Google Patents
Current-limiting protection circuit for low-dropout linear voltage regulator and linear voltage regulator Download PDFInfo
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- G05—CONTROLLING; REGULATING
- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
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- G05F1/46—Regulating voltage or current wherein the variable actually regulated by the final control device is dc
- G05F1/56—Regulating voltage or current wherein the variable actually regulated by the final control device is dc using semiconductor devices in series with the load as final control devices
Abstract
The invention discloses a current-limiting protection circuit for a low-dropout linear voltage regulator and the linear voltage regulator, wherein the current-limiting protection circuit comprises: the device comprises a current sampling unit, a voltage comparison unit and a current limiting loop control unit; the first end of the current-limiting loop control unit is connected with the output end of the voltage comparison unit, the second end of the current-limiting loop control unit is connected with the output end of the current sampling unit, and the third end of the current-limiting loop control unit is connected with the grid electrode of the power tube; the current limiting loop control unit is used for switching on or switching off the current limiting according to the output of the voltage comparison unit, and feeding back the sampling current of the current sampling unit to the grid electrode of the power tube when the current limiting is switched on so as to limit the current flowing through the power tube. The embodiment of the invention can enable the LDO to accurately return to the normal working state in time when the LDO is over-current in a short time, is beneficial to avoiding the repeated restarting of the LDO, especially the LDO with complex starting process, and can reduce the current limiting threshold of the current limiting protection circuit so as to reduce the power of the LDO under the condition of over-current.
Description
Technical Field
The present invention relates to the field of integrated circuits, and more particularly, to a current limiting protection circuit for a low dropout linear voltage regulator and a linear voltage regulator.
Background
In order to protect a low dropout linear regulator (Low Dropout Regulator, LDO) circuit chip from irreversible damage caused by excessive output current or short circuit of an output terminal to ground, a current limiting protection circuit structure needs to be designed to limit the output current of the LDO circuit.
FIG. 1 is a schematic diagram of a current-limiting protection circuit of an LDO according to the prior art, wherein a portion 101 is an LDO loop circuit, a portion 102 is a conventional current-limiting protection circuit, and a first transistor M P1 The current equal to the current of the power tube MP is sampled and compared with the reference current IREF after the current mirror image. When the reference current IREF is greater than the sampling current, the potential of the first node VCON increases to inversely control the second transistor M P2 The gate of (2) is high level, the second transistor M P2 Turn-off, conversely, when the reference current IREF is smaller than the sampling current, the potential of the first node VCON decreases, and the second transistor M is controlled in opposite phase P2 And the power tube MP is opened to limit the voltage drop of the grid electrode of the power tube MP so as to achieve the purpose of current limiting.
Since the first node VCON is not only the second transistor M P2 The control end of the current comparator is the output end of the current-limiting judgment signal, namely the current-limiting control link needs to convert the sampled analog signal into a digital signal, as long as the sampled current is lower than the reference current IREF, the second transistor M P2 The current-limiting threshold is set to be far higher than the normal load current in practical application so as to prevent the false triggering of the current-limiting protection circuit. Because the current flowing through the power tube after current limiting is lower than the current value of normal operation of the power tube, when the LDO only flows excessively for a short time and resumes normal load current, the LDO cannot timely and accurately return to the normal operation state, and in order to protect the LDO from damage, the LDO needs to be powered on again, i.e. reloaded, so that the LDO, in particular the LDO with complicated starting process, is restarted repeatedly.
Disclosure of Invention
The invention provides a current-limiting protection circuit and a linear voltage stabilizer, which can enable an LDO to accurately return to a normal working state in time when the LDO is over-current in a short time, are beneficial to avoiding the repeated restarting of the LDO, especially the LDO with complex starting process, can reduce the current-limiting threshold value of the current-limiting protection circuit so as to reduce the power of the LDO under the condition of over-current, and can enable the sampled current flowing through a power tube to be more accurate, thereby enabling the current flowing through the power tube after the current is limited to be free from the influence of output voltage.
In a first aspect, an embodiment of the present invention provides a current limiting protection circuit for a low dropout linear regulator, including: the device comprises a current sampling unit, a voltage comparison unit and a current limiting loop control unit; the current sampling unit comprises a first input end, a second input end and an output end, wherein the first input end of the current sampling unit is connected with the grid electrode of the low-dropout linear voltage regulator power tube, the second input end of the current sampling unit is connected with the first electrode of the power tube, and the current sampling unit is used for sampling and outputting the current of the power tube; the first input end of the voltage comparison unit is connected with the output end of the current sampling unit, and the second input end of the voltage comparison unit is connected with a first reference voltage; the first end of the current-limiting loop control unit is connected with the output end of the voltage comparison unit, the second end of the current-limiting loop control unit is connected with the output end of the current sampling unit, and the third end of the current-limiting loop control unit is connected with the grid electrode of the power tube; the current limiting loop control unit is used for switching on or switching off the current limiting according to the output of the voltage comparison unit, and feeding back the sampling current of the current sampling unit to the grid electrode of the power tube when the current limiting is switched on so as to limit the current flowing through the power tube.
Optionally, the current-limiting loop control unit is further configured to continue to output and control the gate of the power tube before the load current is restored to the normal operating current and the output voltage of the power tube is restored to the normal operating voltage, and to perform soft shutdown when the output voltage of the power tube is restored to the normal value.
Optionally, the current limiting loop control unit includes a current mirror, a current limiting switch, and a first resistor; the first end of the current mirror is connected with the output end of the current sampling unit, the second end of the current mirror is connected with the grid electrode of the power tube, the third end of the current mirror is connected with the first end of the current limiting switch, the fourth end of the current mirror is connected with the power supply, and the current mirror is used for mirroring the current output by the current sampling unit according to a set proportion and feeding back the current to the grid electrode of the power tube; the control end of the current-limiting switch is connected with the output end of the voltage comparison unit, and the current-limiting switch is used for being turned on or turned off according to the voltage of the output end of the voltage comparison unit; the first end of the first resistor is connected with the second end of the current limiting switch, the second end of the first resistor is connected with the fifth end of the current mirror, and the first resistor is used for soft-switching off the output of the current mirror according to the magnitude of the sampling current.
Optionally, the current mirror comprises a first transistor and a second transistor; the grid electrode of the first transistor is respectively connected with the fifth end of the current mirror and the grid electrode of the second transistor, the first electrode of the first transistor is respectively connected with the grid electrode of the first transistor and the first end of the current mirror, and the second electrode of the first transistor is connected with the fourth end of the current mirror; the first pole of the second transistor is connected with the second end of the current mirror, and the second pole of the second transistor is connected with the third end of the current mirror.
Optionally, the current limiting switch comprises a third transistor; the grid electrode of the third transistor is connected with the control end of the current-limiting switch, the first electrode of the third transistor is connected with the first end of the current-limiting switch, and the second electrode of the third transistor is connected with the second end of the current-limiting switch.
Optionally, the current sampling unit includes a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, and a current source; a grid electrode of the fourth transistor is connected with a grid electrode of the power tube, a first electrode of the fourth transistor is connected with a power supply, and a second electrode of the fourth transistor is connected with a first electrode of the sixth transistor; the grid electrode of the fifth transistor is connected with the grid electrode of the sixth transistor, the first electrode of the fifth transistor is connected with the first electrode of the power transistor, the second electrode of the fifth transistor is connected with the current source, the second electrode of the sixth transistor is connected with the first electrode of the seventh transistor, and the grid electrode of the fifth transistor is connected with the second electrode of the fifth transistor; the grid electrode of the seventh transistor is connected with the grid electrode of the eighth transistor, the second electrode of the seventh transistor is grounded, the first electrode of the eighth transistor is connected with the output end of the current sampling unit, the second electrode of the eighth transistor is grounded, and the grid electrode of the seventh transistor is connected with the first electrode of the seventh transistor.
Optionally, the voltage comparing unit includes a hysteresis comparator, an inverting input end of the hysteresis comparator is connected to a first input end of the voltage comparing unit, a non-inverting input end of the hysteresis comparator is connected to a second input end of the voltage comparing unit, and an output end of the hysteresis comparator is connected to an output end of the voltage comparing unit.
In a second aspect, an embodiment of the present invention provides a linear voltage regulator, including the current limiting protection circuit provided in any one of the above embodiments; the linear voltage stabilizer also comprises an error amplifying unit and a power tube; the first input end of the error amplifying unit is connected with the output end of the linear voltage stabilizer, the second input end of the error amplifying unit is connected with the second reference voltage, the output end of the error amplifying unit is connected with the grid electrode of the power tube, the first pole of the power tube is used as the output end of the linear voltage stabilizer, and the second pole of the power tube is connected with the power supply.
Optionally, the linear voltage stabilizer further comprises a voltage division output unit, wherein the voltage division output unit is connected between the first pole of the power tube and the ground, and the voltage division output unit is used for outputting voltage to the output end of the linear voltage stabilizer according to the current of the power tube.
Optionally, the voltage division output unit comprises a second resistor and a third resistor, the second resistor and the third resistor are connected in series between the first pole of the power tube and the ground, and the common end of the second resistor and the third resistor is connected with the first input end of the error amplifying unit; the linear voltage stabilizer further comprises a capacitor, a first end of the capacitor is connected with the output end of the linear voltage stabilizer, and a second end of the capacitor is grounded.
The embodiment of the invention provides a current-limiting protection circuit for a low-dropout linear voltage regulator, which comprises a current sampling unit, a voltage comparison unit and a current-limiting loop control unit; the current sampling unit is used for sampling the current of the power tube and outputting the sampled current; the voltage comparison unit is used for outputting control voltage to the current-limiting loop control unit according to the voltage of the first input end and the second input end; the current limiting loop control unit is used for switching on or switching off the current limiting according to the output voltage of the voltage comparison unit, and feeding back the sampling current of the current sampling unit to the grid electrode of the power tube when the current limiting is switched on so as to clamp the current flowing through the power tube. The current limiting protection circuit provided by the embodiment of the invention outputs the digital signal to control the current limiting loop control unit to be turned on or turned off through the voltage comparison unit, the second end of the current limiting loop control unit is connected with the output end of the current sampling unit, and the sampling current is applied to feedback, so that all the input signals in the current limiting loop control unit are analog signals, the process of converting the analog signals into the digital signals is omitted, the current flowing through the power tube after current limiting is not lower than the current value of the normal work of the power tube through the regulation of negative feedback, and therefore, the normal load can be restored for short-time overload, the LDO can be timely and accurately returned to the normal work state, the LDO, especially the repeated restarting of the LDO with complex starting process, is avoided, the current limiting threshold of the current limiting protection circuit is reduced, and the power of the LDO under the condition of overcurrent is reduced. The first input end of the current sampling unit is connected with the grid electrode of the low dropout linear voltage regulator power tube, and the second input end of the current sampling unit is connected with the first electrode (the output end of the LDO) of the power tube, so that the current which flows through the power tube and is sampled by the current sampling unit is more accurate, and the current which flows through the power tube after current limiting is not influenced by output voltage.
It should be understood that the description in this section is not intended to identify key or critical features of the embodiments of the invention or to delineate the scope of the invention. Other features of the present invention will become apparent from the description that follows.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of an LDO current limiting protection circuit according to the prior art;
fig. 2 is a schematic structural diagram of a current limiting protection circuit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a current limiting protection circuit according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a current limiting protection circuit according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of another current limiting protection circuit according to an embodiment of the present invention;
FIG. 6 is a diagram illustrating a current limiting protection circuit according to an embodiment of the present invention;
FIG. 7 is a schematic diagram of a linear voltage regulator according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a structure of another linear voltage regulator according to an embodiment of the present invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
In the existing LDO current limiting protection technology suitable for high-speed and high-current, the traditional current limiting can achieve the function of chip protection. However, since the control signal of the current limiting control link is the output signal of the current comparator, the current limiting threshold needs to be set very high, so that the current limiting control link is difficult to be applied to an application scene with very low current limiting threshold. Because the current flowing through the power tube after current limiting is lower than the current value of the normal work of the power tube, when the LDO only overflows for a short time and recovers the normal load current, the overcurrent protection mode is difficult to recover the LDO to the normal work state, and the LDO needs to be powered on and started again, so that the LDO is recovered to the normal work state.
In view of the above, the embodiment of the invention provides a current limiting protection circuit for a low dropout linear regulator. Fig. 2 is a schematic structural diagram of a current limiting protection circuit according to an embodiment of the present invention, as shown in fig. 2, the current limiting protection circuit includes: a current sampling unit 10, a voltage comparing unit 20 and a current limiting loop control unit 30.
The current sampling unit 10 comprises a first input end, a second input end and an output end, the first input end of the current sampling unit 10 is connected with the grid electrode of the low-dropout linear voltage regulator power tube MP, the second input end of the current sampling unit 10 is connected with the first pole of the power tube MP, and the current sampling unit 10 is used for sampling and outputting the current of the power tube MP.
A first input end of the voltage comparison unit 20 is connected with an output end of the current sampling unit 10, and a second input end of the voltage comparison unit 20 is connected with a first reference voltage VREF1;
the first end of the current-limiting loop control unit 30 is connected with the output end of the voltage comparison unit 20, the second end of the current-limiting loop control unit 30 is connected with the output end of the current sampling unit 20, and the third end of the current-limiting loop control unit 30 is connected with the grid electrode of the power tube MP; the current-limiting loop control unit 30 is configured to turn on or off current limiting according to the output of the voltage comparing unit 20, and when the current limiting is turned on, feedback the sampling current of the current sampling unit 10 to the gate of the power tube MP to limit the current flowing through the power tube MP.
The first pole of the power tube MP is connected to the output terminal of the low dropout linear regulator, that is, the first pole of the power tube MP can be used as the output terminal of the low dropout linear regulator, and the second pole of the power tube is connected to the power source VIN. It can be understood that when the current limiting protection circuit is not operating, the current flowing through the power tube MP is equal to the output current (load current) of the LDO; when the current limiting protection circuit works, the current flowing through the power tube MP is not equal to the load current of the LDO, that is, when the current limiting protection circuit works, the current flowing through the power tube MP can be smaller than the load current of the LDO, and the current flowing through the power tube MP can also be larger than the load current of the LDO.
The current sampling unit 10 samples a current flowing through the power tube MP. The type of the current sampling unit 10 may be an integrated circuit having a current sampling function, or may be a circuit having a current sampling function, which is built by a separate transistor, which is not particularly limited in the present invention. The power tube MP works in a saturation region, and current flowing through the power tube MP
Wherein kn represents the technological parameter of the power tube MP, W/L is the width-to-length ratio of the power tube MP, V GS Representing the voltage between the grid and the source of the power tube MP, V DS Representing the voltage between the drain and source of the power tube MP, V T The threshold voltage of the power tube MP is shown. Therefore, the first input end of the current sampling unit 10 is connected with the grid electrode of the low dropout linear voltage regulator power tube MP, the second input end of the current sampling unit 10 is connected with the first electrode of the power tube MP, and accurate sampling of the current flowing through the power tube MP can be achieved, so that the current flowing through the power tube after current limiting is not influenced by output voltage, namely, the current flowing through the power tube after current limiting is not influenced by voltage between the drain electrode and the source electrode.
The voltage comparing unit 20 compares the voltage of the output terminal of the current sampling unit 10 with a first reference voltage VREF1, and generates a control voltage for controlling the current limiting loop control unit 30. Alternatively, the voltage comparing unit 20 may be provided with the high-precision first reference voltage VREF1 by a reference voltage source. The first input terminal of the voltage comparing unit 20 may be a non-inverting input terminal or an inverting input terminal; the second input terminal of the voltage comparing unit 20 may be a non-inverting input terminal or an inverting input terminal.
The current limit loop control unit 30 turns on or off the current limit according to the output of the voltage comparing unit 20. Illustratively, when the voltage comparing unit 20 outputs a high level, the current limiting loop control unit 30 turns off the current limiting; when the voltage comparing unit 20 outputs a low level, the current limiting loop control unit 30 turns on the current limiting, and feeds back the sampling current of the current sampling unit 10 to the gate of the power tube MP to clamp the current flowing through the power tube MP.
With continued reference to fig. 2, the working principle of the current-limiting protection circuit for the low dropout linear regulator is as follows: the current sampling unit 10 samples and outputs the current of the power tube MP, and the voltage comparing unit 20 compares the voltage at the output end of the current sampling unit 10 with the first reference voltage VREF1 to generate a control voltage for controlling the current limiting loop control unit 30; the current limit loop control unit 30 turns on or off the current limit according to the output of the voltage comparing unit 20. Illustratively, when the voltage at the output terminal of the current sampling unit 10 is less than the first reference voltage VREF1, the voltage comparing unit 20 outputs a high level, and the current limiting loop control unit 30 turns off the current limiting; when the voltage at the output end of the current sampling unit 10 is greater than the first reference voltage VREF1, the voltage comparing unit 20 outputs a low level, the current limiting loop control unit 30 starts current limiting, and the sampling current of the current sampling unit 10 is fed back to the gate of the power tube MP to limit the current flowing through the power tube MP.
The current limiting protection circuit comprises a current sampling unit, a voltage comparison unit and a current limiting loop control unit; the current sampling unit is used for sampling the current of the power tube and outputting the sampled current; the voltage comparison unit is used for outputting control voltage to the current-limiting loop control unit according to the voltage of the first input end and the second input end; the current limiting loop control unit is used for switching on or switching off the current limiting according to the output voltage of the voltage comparison unit, and feeding back the sampling current of the current sampling unit to the grid electrode of the power tube when the current limiting is switched on so as to limit the current flowing through the power tube. The current limiting protection circuit provided by the embodiment of the invention outputs the digital signal to control the current limiting loop control unit to be turned on or turned off through the voltage comparison unit, the second end of the current limiting loop control unit is connected with the output end of the current sampling unit, and the sampling current is applied to feedback, so that all the input current in the current limiting loop control unit is analog signals, no process of converting the analog signals into the digital signals is performed, the current flowing through the power tube after current limiting is not lower than the current value of the normal operation of the power tube, and therefore, the normal load can be restored in a short time and accurately, the LDO can be returned to the normal operation state in time, the repeated restarting of the LDO, especially the LDO with complex starting process is avoided, and the current limiting threshold of the current limiting protection circuit is reduced, so that the power under the condition of LDO overcurrent is reduced. The first input end of the current sampling unit is connected with the grid electrode of the low dropout linear voltage regulator power tube, and the second input end of the current sampling unit is connected with the first electrode (the output end of the LDO) of the power tube, so that the current which flows through the power tube and is sampled by the current sampling unit is more accurate, and the current which flows through the power tube after current limiting is not influenced by output voltage.
Fig. 3 is a schematic structural diagram of another current limiting protection circuit according to an embodiment of the present invention, where, based on the above embodiments, as shown in fig. 3, the current limiting loop control unit 30 is further configured to continue to output and control the gate of the power tube MP before the load current is restored to the normal operating current and the output voltage of the power tube MP is restored to the normal operating voltage, and to be turned off softly when the output voltage of the power tube MP is restored to the normal value.
The soft-off refers to a process in which the gate voltage of the transistor in the current-limiting loop control unit 30 slowly drops when the output voltage of the power transistor MP is restored to a normal value, that is, the conduction channel between the drain and the source of the transistor is not completely lost.
Specifically, when the load current is recovered to be normal, that is, the current sampled by the current sampling unit 10 is gradually reduced, in the process, the current limiting loop control unit 30 works together with the LDO main loop to prevent the LDO main loop from rapidly pulling up the large current caused by the output voltage of the power tube MP; when the load current is recovered to the normal working current and before the output voltage of the power tube MP is recovered to the normal working voltage, the current-limiting loop control unit 30 is turned off in a soft way, the LDO main loop works, the LDO main loop stabilizes the output voltage, and when the voltage signal at the output end of the voltage comparison unit 20 is turned from a low level to a high level, the current-limiting loop control unit 30 is turned off thoroughly.
The current limiting loop control unit 30 includes a current mirror 301, a current limiting switch 302, and a first resistor R1; the first end of the current mirror 301 is connected with the output end of the current sampling unit 10, the second end of the current mirror 301 is connected with the grid electrode of the power tube MP, the third end of the current mirror 301 is connected with the first end of the current limiting switch 302, the fourth end of the current mirror 302 is connected with the power source VIN, and the current mirror 301 is used for mirroring the current output by the current sampling unit 10 according to a set proportion and feeding back and outputting the current to the grid electrode of the power tube MP; the control end of the current limiting switch 301 is connected to the output end of the voltage comparing unit 20, and the current limiting switch 302 is used for switching on or switching off according to the voltage of the output end of the voltage comparing unit 20; the first end of the first resistor R1 is connected to the second end of the current limiting switch 302, the second end of the first resistor R1 is connected to the fifth end of the current mirror 301, and the first resistor R1 is used for soft-switching off the output of the current mirror 301 according to the magnitude of the sampling current.
Specifically, since the first resistor R1 is a fixed resistor, the resistance value is unchanged, but the resistance of the channel between the source and the drain of the transistor in the current mirror 301 will become larger along with the decrease of the sampling current, so when the load current returns to the normal working current and before the output voltage of the power tube MP returns to the normal working voltage, the sampling current at the output end of the current sampling unit 10 mainly flows through the first resistor R1, so that the current mirror 301 shunts the smaller tail current source, soft turn-off of the current-limiting loop control unit 30 is realized, the output voltage of the power tube MP is slowly restored in a current-limiting manner, and when the voltage signal at the output end of the voltage comparing unit 20 is turned from low level to high level, the current-limiting loop control unit 30 is thoroughly turned off.
With continued reference to fig. 3, the working principle of the current-limiting protection circuit for the low dropout linear regulator is as follows: the current sampling unit 10 samples and outputs the current of the power tube MP, and the voltage comparing unit 20 compares the voltage at the output end of the current sampling unit 10 with the first reference voltage VREF1 to generate a control voltage for controlling the current limiting loop control unit 30; the current limit switch 302 turns on or off the current limit according to the output of the voltage comparing unit 20. Illustratively, when the voltage at the output terminal of the current sampling unit 10 is less than the first reference voltage VREF1, the voltage comparing unit 20 outputs a high level, the current limiting switch 302 is turned off, and the current mirror 301 does not operate; when the voltage at the output end of the current sampling unit 10 is greater than the first reference voltage VREF1, the voltage comparing unit 20 outputs a low level, and the current limiting switch 302 is turned on. The first process: the current mirror 301 mirrors the current output by the current sampling unit 10 according to a set proportion and feeds back the current to the gate of the power tube MP to clamp the current flowing through the power tube MP, and at this time, the output voltage VOUT of the LDO drops. The second process: before the load current is restored to the normal operating current and the output voltage VOUT of the LDO is restored to the normal operating voltage, the transistor in the current mirror 301 is turned off (the current-limiting loop control unit 30 is still operated at this time) because of the first resistor R1, the LDO main loop continues to operate, and when the output voltage of the LDO is restored to the normal operating voltage, the voltage signal at the output end of the hysteresis comparator 201 is turned from low level to high level, and the current-limiting switch 302 is turned off, i.e., the current-limiting loop control unit 30 is turned off, and the LDO main loop stabilizes the output voltage VOUT. If the load current is still in an overcurrent state within a certain counting time, an overcurrent signal is sent out, the LDO and the current limiting protection circuit are turned off, and the current of the power tube MP is continuously sampled through the current sampling unit 10 after restarting. Before the load current is restored to the normal working current and the output voltage VOUT of the LDO is restored to the normal working voltage, the transistor in the current mirror 301 is turned off through the first resistor R1, which is beneficial to avoiding repeated restarting of the LDO. When the output voltage of the LDO is recovered to the normal working voltage, the voltage signal at the output end of the hysteresis comparator 201 is turned from low level to high level, and the current-limiting switch 302 is turned off, i.e. the current-limiting loop control unit 30 is turned off, so that the LDO main loop stabilizes the output voltage VOUT, and the LDO can be timely and accurately returned to the normal working state.
Fig. 4 is a schematic structural diagram of another current limiting protection circuit according to an embodiment of the present invention, where, based on the above embodiments, as shown in fig. 4, a current mirror 301 includes a first transistor M1 and a second transistor M2; the gate of the first transistor M1 is connected to the fifth end of the current mirror 301 and the gate of the second transistor M2, respectively, the first pole of the first transistor M1 is connected to the gate of the first transistor M1 and the first end of the current mirror 301, respectively, and the second pole of the first transistor M1 is connected to the fourth end of the current mirror 301; a first pole of the second transistor M2 is connected to the second terminal of the current mirror 301, and a second pole of the second transistor M2 is connected to the third terminal of the current mirror 301.
The current limit switch 302 includes a third transistor M3; the gate of the third transistor M3 is connected to the control terminal of the current-limiting switch 301, the first pole of the third transistor M3 is connected to the first terminal of the current-limiting switch 301, and the second pole of the third transistor M2 is connected to the second terminal of the current-limiting switch 302.
Fig. 5 IS a schematic diagram of a current limiting protection circuit according to another embodiment of the present invention, where, based on the above embodiments, as shown in fig. 5, the current sampling unit 10 includes a fourth transistor M4, a fifth transistor M5, a sixth transistor M6, a seventh transistor M7, an eighth transistor M8, and a current source IS.
The grid electrode of the fourth transistor M4 is connected with the grid electrode of the power tube MP, the first electrode of the fourth transistor M4 is connected with the power source VIN, and the second electrode of the fourth transistor M4 is connected with the first electrode of the sixth transistor M6; the gate of the fifth transistor M5 IS connected to the gate of the sixth transistor M6, the first pole of the fifth transistor M5 IS connected to the first pole of the power transistor MP, the second pole of the fifth transistor M5 IS connected to the current source IS, the second pole of the sixth transistor M6 IS connected to the first pole of the seventh transistor M7, and the gate of the fifth transistor M5 IS connected to the second pole of the fifth transistor M5; the gate of the seventh transistor M7 is connected to the gate of the eighth transistor M8, the second pole of the seventh transistor M7 is grounded, the first pole of the eighth transistor M8 is connected to the output terminal of the current sampling unit 10, the second pole of the eighth transistor M8 is grounded, and the gate of the seventh transistor M7 is connected to the first pole of the seventh transistor M7.
The current flowing through the second transistor M2 during current limiting is constant as the tail current of the error amplifier in the LDO, and the output end of the error amplifier is connected with the gate of the power tube MP. The fourth transistor M4 mirrors the current of the power transistor MP, and the size ratio of the fourth transistor M4 to the power transistor MP is 1: n. N is generally in the range of 1000 to 100000. Where N represents the aspect ratio of the fourth transistor M4.
Optionally, the size ratio of the fifth transistor M5 to the sixth transistor is 1:1, and the size ratio of the seventh transistor M7 to the eighth transistor M8 is 1:1. When the ratio of the current flowing through the fourth transistor M4 to the current flowing through the second transistor M2 is k:1, the ratio of the current flowing through the power transistor MP to the current flowing through the fourth transistor M4 is N:1, the current flowing through the power transistor MP is constant at iout=n×k×il, and IL is the tail current of the error amplifier in the LDO. The voltage of the first pole of the sixth transistor M6 is equal to the output voltage VOUT of the LDO (i.e., the output voltage of the power transistor MP) through the first current mirror formed by the fifth transistor M5 and the sixth transistor M6, so that the sampling accuracy of the fourth transistor M4 can be improved.
The working process of the current sampling unit 10 is as follows:
when the current flowing through the power transistor MP is smaller, the current mirrored to the fourth transistor M4 is also smaller, and the voltage of the first pole of the sixth transistor M6 is equal to the output voltage VOUT of the LDO (i.e., the output voltage of the power transistor MP) through the first current mirror formed by the fifth transistor M5 and the sixth transistor M6, and the current is mirrored to the second current mirror formed by the seventh transistor M7 and the eighth transistor M8.
The first transistor M1, the second transistor M2, and the third transistor M3 of the current-limiting loop control unit 30, the fourth transistor M4, the fifth transistor M5, and the sixth transistor M6 of the current sampling unit 10 each include PMOS, and the seventh transistor M7 and the eighth transistor M8 each include NMOS.
The voltage comparison unit 20 comprises a hysteresis comparator 201, wherein an inverting input end of the hysteresis comparator 201 is connected with a first input end of the voltage comparison unit 20, a non-inverting input end of the hysteresis comparator 201 is connected with a second input end of the voltage comparison unit 20, and an output end of the hysteresis comparator 201 is connected with an output end of the voltage comparison unit 20.
The hysteresis comparator 201 has two threshold voltages. When the voltage of the inverting input terminal is changed from large to small, corresponding to the lower threshold voltage, and when the voltage is smaller than the lower threshold voltage by a little, the output jumps to high level; when the voltage input of the inverting input terminal is changed from small to large, the output jumps to low level when the voltage input is corresponding to the upper threshold voltage and is larger than the upper threshold voltage by a little. Between the two threshold voltages, the output remains the original output. Therefore, the first reference voltage VREF1 may vary with the inversion of the output.
With continued reference to fig. 5, the working principle of the current-limiting protection circuit for the low dropout linear regulator is as follows: the fourth transistor M4 samples the current of the power transistor MP, the seventh transistor M7 is a mirrored transistor, the sampled current is mirrored to the eighth transistor M8 of the mirrored transistor and then output, the hysteresis comparator 201 compares the voltage at the output end of the current sampling unit 10 with the first reference voltage VREF1 (the first reference voltage VREF1 will change along with the inversion of the output), and a control voltage for controlling the current-limiting loop control unit 30 is generated; the third transistor M3 turns on or off the current limit according to the hysteresis comparator 201 output. Illustratively, when the voltage at the output terminal of the current sampling unit 10 is reduced from large to small, which is a little smaller than the first reference voltage VREF1 (when the first reference voltage VREF1 is a negative voltage), the voltage comparing unit 20 outputs a high level, the third transistor M3 is turned off, and the current mirror 301 does not operate; when the voltage at the output end of the current sampling unit 10 is changed from small to large, and is slightly larger than the first reference voltage VREF1 (the first reference voltage VREF1 is a positive voltage at this time), the voltage comparing unit 20 outputs a low level, and the third transistor M3 is turned on, and this operation stage is divided into two processes. The first process: the current mirror 301 mirrors the current output by the current sampling unit 10 according to a set proportion and feeds back the current to the gate of the power tube MP to clamp the current flowing through the power tube MP, and at this time, the output voltage VOUT of the LDO drops. The second process: before the load current is restored to the normal operating current and the output voltage VOUT of the LDO is restored to the normal operating voltage, the first transistor M1 and the second transistor M2 in the current mirror 301 are turned off (the first transistor M1 and the second transistor M2 still operate at this time) because of the first resistor R1, the LDO main loop continues to operate, and when the output voltage of the LDO is restored to the normal operating voltage, the voltage signal at the output terminal of the hysteresis comparator 201 is turned from low level to high level, the third transistor M3 is turned off, that is, the current limiting loop control unit 30 is turned off, and the LDO main loop stabilizes the output voltage VOUT. If the load current is still in an overcurrent state within a certain counting time, an overcurrent signal is sent out, the LDO and the current limiting protection circuit are turned off, and the current of the power tube MP is continuously sampled through the fourth transistor M4 after restarting. Before the load current is restored to the normal working current and the output voltage VOUT of the LDO is restored to the normal working voltage, the first transistor M1 and the second transistor M2 are turned off through the first resistor R1, which is beneficial to avoiding repeated restarting of the LDO.
Fig. 6 is a graph of a working process of the current limiting protection circuit according to the embodiment of the present invention, as shown in fig. 6, the working process graph may be applicable to the current limiting protection circuit shown in fig. 5. Referring to fig. 5 and 6, illustratively, 601 represents a current curve (load current curve) flowing through a load, 602 represents a current curve flowing through a power tube MP, 603 represents an output voltage curve of an LDO, and the operation of the current limiting protection circuit includes a plurality of stages.
In the first stage t1, i.e. the LDO is in the normal operation stage, the current flowing through the power tube MP is smaller than the current limiting threshold ICL, and the current limiting loop control unit 30 is not operated at this time, and the current flowing through the power tube MP is equal to the load current. When the load current rises to the current limit threshold ICL, the hysteresis comparator 201 issues a current limit signal, which opens the current limit loop control unit 30, and enters the second phase t2 of the current limit process.
In the second stage t2, the load current is near the current limiting threshold ICL, the current limiting loop control unit 30 works to limit the current flowing through the power tube MP to be lower than the load current, so that the output voltage VOUT of the LDO is reduced, the power in the LDO chip is reduced, and the purpose of protecting the LDO chip is achieved.
In the third stage t3, the load current is restored to the normal operating current IOUT, nom, before the output voltage of the LDO is restored to the normal operating voltage VOUT, nom, the first transistor M1 and the second transistor M2 are turned off (the current-limiting loop control unit 30 is still operated at this time) because of the first resistor R1, so as to prevent the LDO main loop from rapidly pulling up the large current caused by the output voltage VOUT of the LDO, and when the output voltage VOUT of the LDO is restored to the normal operating voltage VOUT, nom, the voltage signal at the output end of the hysteresis comparator 201 is turned from low level to high level, and the third transistor M3 is turned off (i.e., the current-limiting loop control unit 30 is turned off), so that the LDO main loop stabilizes the output voltage VOUT.
Fig. 7 is a schematic structural diagram of a linear voltage regulator according to an embodiment of the present invention, as shown in fig. 7, where the linear voltage regulator includes the current limiting protection circuit according to any one of the above embodiments. Fig. 7 schematically shows a case where the linear voltage regulator includes the current limiting protection circuit provided in fig. 5.
The linear voltage stabilizer also comprises an error amplifying unit 40 and a power tube MP; the first input end of the error amplifying unit 40 is connected with the output end of the linear voltage stabilizer, the second input end of the error amplifying unit 40 is connected with the second reference voltage VREF2, the output end of the error amplifying unit 40 is connected with the grid electrode of the power tube MP, the first pole of the power tube MP is used as the output end of the linear voltage stabilizer, and the second pole of the power tube MP is connected with the power supply VIN.
The error amplifying unit 40 may be a single channel class AB gain with PMOS differential input pair. The error amplifying unit 40 compares the feedback voltage with the second reference voltage VREF2 to generate an error voltage for controlling the gate of the power transistor MP, and adjusts the on-current flowing through the power transistor MP to stabilize the output voltage VOUT of the LDO. Wherein the error amplifying unit 10 can be provided with a high-precision reference voltage VREF2 by a reference voltage source. The first input terminal of the error amplifying unit 40 may be a non-inverting input terminal or an inverting input terminal; the second input terminal of the error amplifying unit 40 may be a non-inverting input terminal or an inverting input terminal. Fig. 7 schematically shows a case where the first input terminal of the error amplifying unit 40 is a non-inverting input terminal and the second input terminal of the error amplifying unit 40 is an inverting input terminal.
The power tube MP is also called a regulator tube, and its main function is to input a channel for supplying a large current to a load. The second pole of the power tube MP is connected with the power supply VIN, and the first pole of the power tube MP is connected with the output end of the LDO. That is, the first pole of the power transistor MP may be the output terminal of the LDO. The power tube MP includes, but is not limited to, NPN tube, PNP tube, PMOS tube, or NMPS tube. Fig. 7 schematically shows a case where the power transistor MP adopts a PMOS transistor. The output voltage VOUT at the output of the linear regulator drives the load to which it is connected. In addition, the channel length of the power tube MP is generally smaller and the width thereof is larger, that is, the width-to-length ratio of the power tube MP is generally larger, generally greater than or equal to 1000, so that the gate of the power tube MP has larger parasitic capacitance.
The working principle of the linear voltage stabilizer is that the output current flowing through the power tube MP is regulated through the negative feedback function, so that the output voltage VOUT is kept stable. With continued reference to fig. 7, the second reference voltage VREF2 is coupled to the inverting input of the error amplifying unit 40, and the output voltage VOUT couples the generated feedback voltage to the non-inverting input of the error amplifying unit 40 through a feedback network. When the output voltage VOUT decreases, the output voltage VOUT is transmitted to the non-inverting input terminal of the error amplifying unit 40 through the feedback network, the voltage at the inverting input terminal of the error amplifying unit 40 decreases, the difference between the second reference voltage VREF2 and the feedback voltage decreases, the gate voltage of the power transistor MP decreases, the difference between the gate and source voltages increases, the drain current of the power transistor MP increases, i.e., the output current increases, the output voltage VOUT increases, and further decrease of the output voltage VOUT is suppressed, so that the output voltage VOUT remains stable. Conversely, when the output voltage VOUT increases, the voltage at the non-inverting input terminal of the error amplifying unit 40 increases, the difference between the second reference voltage VREF2 and the feedback voltage increases, the gate voltage of the power transistor MP increases, the drain current of the power transistor MP decreases, i.e., the output current of the LDO decreases, and the output voltage VOUT decreases. Thus, the linear voltage stabilizer is always in a deep negative feedback state to continuously correct the output voltage VOUT, so that the output voltage VOUT is always stable.
Fig. 8 is a schematic structural diagram of another linear voltage regulator according to an embodiment of the present invention, where, as shown in fig. 8, the linear voltage regulator further includes a voltage division output unit 50, the voltage division output unit 50 is connected between a first pole of the power tube MP and ground, and the voltage division output unit 50 is configured to output a voltage to an output terminal of the linear voltage regulator according to a current of the power tube MP.
The voltage division output unit 50 comprises a second resistor R2 and a third resistor R3, the second resistor R2 and the third resistor R3 are connected in series between a first pole of the power tube MP and the ground, and a common end of the second resistor R2 and the third resistor R3 is connected with a first input end of the error amplifying unit 40;
the linear voltage stabilizer further comprises a capacitor CL, a first end of the capacitor CL is connected with the output end of the linear voltage stabilizer, and a second end of the capacitor CL is grounded.
The working process of the linear voltage stabilizer is as follows:
the second resistor R2 and the third resistor R3 collect the output voltage VOUT of the output terminal of the linear voltage regulator, input the collected voltage to the non-inverting input terminal of the error amplifying unit 40, compare with the second reference voltage VREF2 of the inverting input terminal of the error amplifying unit 40, amplify the comparison result, and output the amplified signal to the gate of the power tube MP.
When the output voltage VOUT drops due to load variation or other reasons, that is, the voltage at the common terminal a drops, the potential at the common terminal a is transmitted to the non-inverting input terminal (first input terminal) of the error amplifying unit 40 through the feedback network, and compared with the second reference voltage VREF2 at the inverting input terminal (second input terminal) of the error amplifying unit 40, the output voltage of the error amplifying unit 40 is reduced, so that the voltage at the gate of the power tube MP drops, the voltage at the source of the power tube MP is unchanged, further the absolute value |vgs| of the differential pressure between the gate and the source of the power tube MP increases, the drain current of the power tube MP increases, the output current increases, and the capacitor CL is charged, so that the output voltage VOUT rises, and one feedback control is completed, so that the potential at the common terminal a returns to the normal potential.
When the output voltage VOUT increases, the voltage at the common terminal a increases, the output voltage of the error amplifying unit 40 increases, so that the voltage at the gate of the power tube MP increases, the voltage at the source of the power tube MP does not change, and further the absolute value |vgs| of the voltage difference between the gate and the source of the power tube MP decreases, the drain current of the power tube MP decreases, the output current decreases, the capacitor CL discharges to supply current to the load, and the output voltage VOUT at the output terminal of the LDO decreases. Therefore, the feedback voltage fed back to the error amplifying unit 40 is also reduced, the output voltage of the error amplifying unit 40 is reduced, the voltage of the gate electrode of the power tube MP connected to the output end of the error amplifying unit 40 is pulled down, the absolute value |vgs| of the voltage difference between the gate electrode and the source electrode of the power tube MP is increased, the output current of the load is increased, the capacitor CL stops discharging, the output voltage VOUT of the LDO output end is not reduced any more, and the voltage starts to rise. Therefore, the linear voltage stabilizer is always in a deep negative feedback state, and continuously corrects the output voltage VOUT of the LDO output end, so that the output voltage VOUT of the LDO output end is always stable.
The above embodiments do not limit the scope of the present invention. It will be apparent to those skilled in the art that various modifications, combinations, sub-combinations and alternatives are possible, depending on design requirements and other factors. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of the present invention.
Claims (10)
1. A current limiting protection circuit for a low dropout linear voltage regulator, comprising: the device comprises a current sampling unit, a voltage comparison unit and a current limiting loop control unit;
the current sampling unit comprises a first input end, a second input end and an output end, wherein the first input end of the current sampling unit is connected with a grid electrode of a low-dropout linear voltage regulator power tube, the second input end of the current sampling unit is connected with a first electrode of the power tube, and the current sampling unit is used for sampling and outputting the current of the power tube;
the first input end of the voltage comparison unit is connected with the output end of the current sampling unit, and the second input end of the voltage comparison unit is connected with a first reference voltage;
the first end of the current-limiting loop control unit is connected with the output end of the voltage comparison unit, the second end of the current-limiting loop control unit is connected with the output end of the current sampling unit, and the third end of the current-limiting loop control unit is connected with the grid electrode of the power tube; the current limiting loop control unit is used for switching on or switching off current limiting according to the output of the voltage comparison unit, and feeding back the sampling current of the current sampling unit to the grid electrode of the power tube when the current limiting is switched on so as to limit the current flowing through the power tube.
2. The current limiting protection circuit according to claim 1, wherein the current limiting loop control unit is further configured to continue to output and control the gate of the power tube before the load current returns to the normal operation current and the output voltage of the power tube returns to the normal operation voltage, and to be turned off softly when the output voltage of the power tube returns to the normal value.
3. The current limiting protection circuit according to claim 1 or 2, wherein the current limiting loop control unit comprises a current mirror, a current limiting switch and a first resistor; the first end of the current mirror is connected with the output end of the current sampling unit, the second end of the current mirror is connected with the grid electrode of the power tube, the third end of the current mirror is connected with the first end of the current limiting switch, the fourth end of the current mirror is connected with a power supply, and the current mirror is used for reducing the current output by the current sampling unit according to a set proportion in a mirror image mode and feeding back and outputting the current to the grid electrode of the power tube; the control end of the current limiting switch is connected with the output end of the voltage comparison unit, and the current limiting switch is used for being turned on or turned off according to the voltage of the output end of the voltage comparison unit; the first end of the first resistor is connected with the second end of the current limiting switch, the second end of the first resistor is connected with the fifth end of the current mirror, and the first resistor is used for soft-switching off the output of the current mirror according to the magnitude of the sampling current.
4. A current limiting protection circuit according to claim 3, wherein the current mirror comprises a first transistor and a second transistor;
the grid electrode of the first transistor is respectively connected with the fifth end of the current mirror and the grid electrode of the second transistor, the first pole of the first transistor is respectively connected with the grid electrode of the first transistor and the first end of the current mirror, and the second pole of the first transistor is connected with the fourth end of the current mirror; the first pole of the second transistor is connected with the second end of the current mirror, and the second pole of the second transistor is connected with the third end of the current mirror.
5. A current limiting protection circuit according to claim 3, wherein the current limiting switch comprises a third transistor;
the grid electrode of the third transistor is connected with the control end of the current-limiting switch, the first electrode of the third transistor is connected with the first end of the current-limiting switch, and the second electrode of the third transistor is connected with the second end of the current-limiting switch.
6. The current limiting protection circuit of claim 1, wherein the current sampling unit comprises a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor, an eighth transistor, and a current source;
The grid electrode of the fourth transistor is connected with the grid electrode of the power tube, the first electrode of the fourth transistor is connected with a power supply, and the second electrode of the fourth transistor is connected with the first electrode of the sixth transistor;
the grid electrode of the fifth transistor is connected with the grid electrode of the sixth transistor, the first electrode of the fifth transistor is connected with the first electrode of the power transistor, the second electrode of the fifth transistor is connected with the current source, the second electrode of the sixth transistor is connected with the first electrode of the seventh transistor, and the grid electrode of the fifth transistor is connected with the second electrode of the fifth transistor;
the grid electrode of the seventh transistor is connected with the grid electrode of the eighth transistor, the second electrode of the seventh transistor is grounded, the first electrode of the eighth transistor is connected with the output end of the current sampling unit, the second electrode of the eighth transistor is grounded, and the grid electrode of the seventh transistor is connected with the first electrode of the seventh transistor.
7. The current limiting protection circuit of claim 1, wherein the voltage comparison unit comprises a hysteresis comparator, an inverting input of the hysteresis comparator is connected to a first input of the voltage comparison unit, a non-inverting input of the hysteresis comparator is connected to a second input of the voltage comparison unit, and an output of the hysteresis comparator is connected to an output of the voltage comparison unit.
8. A linear voltage regulator comprising the current limiting protection circuit of any one of claims 1-7;
the linear voltage stabilizer also comprises an error amplifying unit and a power tube;
the first input end of the error amplifying unit is connected with the output end of the linear voltage stabilizer, the second input end of the error amplifying unit is connected with a second reference voltage, the output end of the error amplifying unit is connected with the grid electrode of the power tube, the first electrode of the power tube is used as the output end of the linear voltage stabilizer, and the second electrode of the power tube is connected with a power supply.
9. The linear voltage regulator of claim 8, further comprising a voltage division output unit connected between the first pole of the power tube and ground, the voltage division output unit configured to output a voltage to an output terminal of the linear voltage regulator according to a current of the power tube.
10. The linear voltage regulator of claim 8, wherein the voltage division output unit comprises a second resistor and a third resistor, the second resistor and the third resistor are connected in series between a first pole of the power tube and ground, and a common terminal of the second resistor and the third resistor is connected with a first input terminal of the error amplification unit;
The linear voltage stabilizer further comprises a capacitor, wherein a first end of the capacitor is connected with the output end of the linear voltage stabilizer, and a second end of the capacitor is grounded.
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