Current stepping turn-back protection circuit

Abstract

The invention discloses a current stepping turn-back protection circuit which is applied to a low-dropout linear voltage regulator, so that current stepping turn-back protection can be realized without arranging high-power-consumption devices such as a voltage comparator in the low-dropout linear voltage regulator. The cost of setting current stepping turn-back protection in the low dropout linear regulator is reduced; according to the low-dropout linear regulator with the current stepping turn-back protection function, the power consumption in the circuit is reduced while the output current is controlled, the purpose that the current stepping turn-back protection technology is applied to the low-power-consumption scene of the low-dropout linear regulator can be further achieved, the operation power consumption of the low-dropout linear regulator with the current stepping turn-back protection function is reduced, and the service life of the low-dropout linear regulator is prolonged. And the implementation scheme of realizing the current stepping turn-back protection function in the low-dropout linear voltage regulator by a user is simplified.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current step-back protection, and in particular to a current step-back protection circuit. BACKGROUND

[0002] In the use of LDO (Low Dropout Regulator) with current step-back protection, current protection can effectively prevent damage to devices caused by excessive load current. Among them, current step-back protection is a common function of overcurrent protection, which can reduce the output current according to the output voltage condition to prevent the output power tube from being damaged by heat, and can also protect the entire circuit system to further ensure the stable operation of the system.

[0003] At present, the LDO structure with current step-back protection function generally includes a voltage comparison circuit, a current comparison circuit, a current limiting circuit, etc. The circuit module for realizing the current step-back protection function is generally the voltage comparison circuit, which will have one or more comparators inside for comparing and determining whether the output voltage is lower than the threshold value, and then reducing the reference current size in the current comparison circuit to control the current limiting circuit to limit the current output by the LDO, thereby completing the current step-back protection function. However, the traditional current step-back protection structure is too complex to implement, and the cost is too high, which will increase the normal working power consumption of the LDO, making it difficult to apply the implementation scheme of this technology to low-power requirements. SUMMARY

[0004] To solve the above technical problems, the present application provides a current step-back protection circuit applied to a low dropout regulator, which includes an operational amplifier, an output circuit, a current feedback circuit and a voltage dividing circuit.

[0005] The first input end of the current step-back protection circuit is connected with the output circuit, and the second input end of the current step-back protection circuit is connected with the voltage dividing circuit.

[0006] The voltage dividing circuit is connected with the first input end of the operational amplifier, and the output end of the current step-back protection circuit is connected with the second input end of the operational amplifier through the current feedback circuit.

[0007] Among them, the third input end of the operational amplifier is used to receive a reference voltage, the output end of the operational amplifier is connected with the output circuit, and the output circuit is connected with the current feedback circuit and the voltage dividing circuit.

[0008] The voltage dividing circuit is configured to output a first feedback voltage to the operational amplifier, and the current step foldback protection circuit is configured to output a second feedback voltage to the operational amplifier through the current feedback circuit.

[0009] The current step foldback protection circuit comprises a first transistor, a current source and a flip-flop.

[0010] The first input end of the first transistor is connected with the output circuit, the second input end of the first transistor is connected with the voltage dividing circuit, the output end of the first transistor is connected with the first end of the current source, the second end of the current source is grounded, the first end of the current source is connected with the first end of the flip-flop, and the second end of the flip-flop is connected with the current feedback circuit.

[0011] The first transistor is configured to detect voltage change of the voltage dividing circuit and output current to the current source based on the voltage change on the voltage dividing circuit, and the flip-flop is configured to output a current signal to the current feedback circuit based on the current output by the first transistor and the current of the current source, so as to control the second feedback voltage output by the current feedback circuit to the operational amplifier.

[0012] The voltage dividing circuit comprises a first resistor, a second resistor and a third resistor, the first end of the first resistor is connected with the output circuit, the second end of the first resistor is connected with the first end of the third resistor through the second resistor, and the second end of the third resistor is grounded; the second end of the first resistor is connected with the second input end of the first transistor, and the first end of the third resistor is connected with the second input end of the operational amplifier, so as to output the first feedback voltage to the operational amplifier.

[0013] The first transistor is configured to output current according to voltage drop on the first resistor, so as to control the second feedback voltage output by the current feedback circuit to the operational amplifier.

[0014] The current feedback circuit comprises a second transistor, a third transistor, a fourth resistor, a fifth resistor, a sixth resistor and a seventh resistor.

[0015] The first input end of the second transistor is connected with the output circuit through the fifth resistor, the second input end of the second transistor is connected with the second input end of the third transistor, and the output end of the second transistor is grounded; the first input end of the third transistor is connected with the output circuit through the sixth resistor, the second input end of the third transistor is connected with the second end of the flip-flop, and the output end of the third transistor is grounded.

[0016] a first end of the fifth resistor is connected with a first end of the fourth resistor, a second end of the fifth resistor is grounded, a first end of the seventh resistor is connected with a first end of the sixth resistor, and a second end of the seventh resistor is grounded;

[0017] a first end of the fifth resistor is connected with a third input end of the operational amplifier.

[0018] The output circuit comprises a fourth transistor, a fifth transistor, a sixth transistor and a seventh transistor,

[0019] a first input end of the fourth transistor and a first input end of the fifth transistor are connected with a power supply, a second input end of the fourth transistor and a second input end of the fifth transistor are connected with an output end of an operational amplifier, an output end of the fourth transistor is connected with a first input end of the sixth transistor, an output end of the fifth transistor is connected with a first input end of the seventh transistor, a second input end of the sixth transistor is connected with a second input end of the seventh transistor, an output end of the sixth transistor and an output end of the seventh transistor are connected with the current feedback circuit, and a second input end of the seventh transistor is connected with an output end of the seventh transistor.

[0020] the output end of the fourth transistor is connected with the current step-back protection circuit and the voltage dividing circuit.

[0021] The output current of the fourth transistor is greater than the output current of the fifth transistor, and the output current of the sixth transistor is equal to the output current of the seventh transistor.

[0022] When the first feedback voltage is greater than the second feedback voltage, the set output voltage of the low-dropout linear regulator is a product of the reference voltage and a first coefficient, and the first coefficient is equal to a sum of resistances of the first resistor, the second resistor and the third resistor divided by the resistance of the third resistor.

[0023] When the first feedback voltage is less than or equal to the second feedback voltage, and the output voltage of the low-dropout linear regulator is greater than a threshold voltage, the output current of the low-dropout linear regulator is limited to a first output current, and the first output current is equal to a product of the reference voltage and a second coefficient divided by a resistance of the fifth resistor and the fourth resistor in parallel, and the second coefficient is a ratio of the output current of the fourth transistor to the output current of the fifth transistor.

[0024] The threshold voltage is equal to a product of a voltage difference between the first input end and the second input end of the first transistor and a third coefficient.

[0025] wherein the third coefficient is a sum of the resistance value of the first resistor, the resistance value of the second resistor and the resistance value of the third resistor divided by the resistance value of the first resistor.

[0026] wherein when the first feedback voltage is less than or equal to the second feedback voltage and the output voltage of the low dropout linear regulator is less than the threshold voltage, the output current of the low dropout linear regulator is limited to a second output current, the second output current is equal to a product of the first output current and a fourth coefficient, and the fourth coefficient is equal to the resistance value of the fourth resistor divided by a sum of the resistance value of the fourth resistor and the resistance value of the fifth resistor.

[0027] The current step back protection circuit provided by the present application is applied to the low dropout linear regulator, so that the current step back protection can be realized in the low dropout linear regulator without setting high-power consumption devices such as voltage comparators, the cost of setting the current step back protection in the low dropout linear regulator is reduced, the power consumption in the circuit is reduced while the output current control is realized, the purpose of applying the current step back protection technology to the low-power consumption scene of the low dropout linear regulator is further achieved, and the implementation scheme of the user for realizing the current step back protection function in the low dropout linear regulator is simplified. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0029] wherein:

[0030] Figure 1 is a schematic diagram of an embodiment of a low dropout linear regulator with current step foldback protection;

[0031] Figure 2 is a structural schematic diagram of an embodiment of the application, which provides a current step foldback protection circuit and a low dropout linear regulator;

[0032] Figure 3 is Figure 2 is a running IV characteristic diagram of a low dropout linear regulator.

[0033] Corresponding reference signs indicate corresponding parts throughout the drawings. The drawings are only given for illustrative purposes and are non-limiting. The drawings show: DETAILED DESCRIPTION

[0034] The scheme of the embodiments of the application will be described in detail below with reference to the accompanying drawings.

[0035] In the following description, for purposes of explanation and not limitation, specific details are set forth such as particular architectures, interfaces, techniques, etc. in order to provide a thorough understanding of the application. However, it will be apparent to those skilled in the art that the application can be practiced in other embodiments that depart from these specific details.

[0036] Reference throughout this specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. It is expressly understood that the described embodiments are merely example structures of the application and that one of ordinary skill in the art would, upon inspective of this application, envision other methods of equivalent structure and / or function.

[0037] The term "and / or" in this application merely describes an associated relationship between associated objects, which means that there can be three relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. In addition, the character " / " in this application generally means that the front and rear associated objects are in an "or" relationship. In addition, "multiple" in this application means two or more than two. In addition, the term "at least one" in this application means any one of multiple or any combination of at least two of multiple, for example, including at least one of A, B and C can mean including any one or more elements selected from the set consisting of A, B and C. In addition, the terms "first", "second", "third" in this application are only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0038] The existing LDO with current step foldback protection function is generally as follows Figure 1As shown, the circuit module mainly realizing the current step-back protection function is a voltage comparison circuit, which internally has one or more comparators for comparing and determining the output voltage with the voltage threshold, and then reducing the reference current in the current comparison circuit, controlling the current limiting circuit to limit the current output by the LDO, to complete the current step-back protection function. However, the traditional current step-back protection structure is too complex to implement, has high implementation cost, and increases the normal working power consumption of the LDO, so that the implementation scheme of this technology is difficult to apply to low-power requirements.

[0039] The application provides a current step-back protection circuit, which, by cooperating with resistance string voltage division and single-stage current source load common-source MOS tube amplification circuit, enables the equivalent back protection threshold voltage to be flexibly set, thereby avoiding the circuit complexity brought by the double-ended comparator, and reducing the implementation cost and power consumption thereof in the low-dropout linear regulator.

[0040] Specifically, please refer to Figure 2 The current step-back protection circuit 1 provided by the application is applied to the low-dropout linear regulator 2 and participates in the circuit back protection process of the low-dropout linear regulator 2. It can be understood that the current step-back protection circuit 1 provided by the application can also participate in the current step-back protection process of other circuit modules that need to set the current step-back protection function.

[0041] The current step-back protection circuit 1 provided by the application is described in detail below in combination with the structure of the low-dropout linear regulator 2:

[0042] The low-dropout linear regulator 2 includes an operational amplifier 11, an output circuit 12, a current feedback circuit 13, and a voltage dividing circuit 14.

[0043] The first input end of the current step-back protection circuit 1 is connected with the output circuit 12, the second input end of the current step-back protection circuit is connected with the voltage dividing circuit, the voltage dividing circuit 14 is connected with the first input end of the operational amplifier 11, and the current step-back protection circuit 1 is connected with the second input end of the operational amplifier 11 through the current feedback circuit 13.

[0044] The third input end of the operational amplifier 11 is used to receive a reference voltage Vref, the output end of the operational amplifier 11 is connected with the output circuit 12, and the output circuit 12 is also connected with the current feedback circuit 13 and the voltage dividing circuit 14.

[0045] The voltage dividing circuit 14 is used to output a first feedback voltage V FB to the operational amplifier 11, the current step-back protection circuit 1 is used to output a second feedback voltage V OCP_FB to the operational amplifier 11 through the current feedback circuit 13, and the operational amplifier 11 is used to determine the output voltage based on the first feedback voltage V FBSecond feedback voltage V OCP_FB The output parameters of the output circuit 12 are controlled, wherein the output parameters of the output circuit 12 may include at least one of the output current and the output voltage, so as to realize current step back protection for the low dropout linear regulator.

[0046] Specifically, such as Figure 2 As shown, operational amplifier 11 is a three-input operational amplifier U, used to control the entire subsequent loop. It has two positive input terminals and one negative input terminal. The negative input terminal is used to receive the reference voltage, and the two positive input terminals are used to receive the first feedback voltage V respectively. FB Second feedback voltage V OCP_FB Operational amplifier 11 will be based on a signal with a higher voltage input at its two positive input terminals (i.e., the first feedback voltage V). FB Second feedback voltage V OCP_FB The loop is controlled by a feedback voltage with a relatively high voltage value.

[0047] The voltage divider circuit 14 can divide the output voltage Vout of the output circuit 12, that is, the first feedback voltage V FB To provide a voltage that is proportional to the output voltage, the magnitude of the output voltage can be fed back. The current step foldback protection circuit 1 outputs a second feedback voltage V through the current feedback circuit 13. OCP_FB This can be related to the output current. Therefore, the operational amplifier 11 can be based on the first feedback voltage V. FB Or the second feedback voltage V OCP_FB The output parameters of output circuit 12 are controlled.

[0048] In fact, when the low-dropout linear regulator 2 is operating normally, the first feedback voltage V FB It will be equal to the reference voltage Vref, the first feedback voltage V FB Greater than the second feedback voltage V OCP_FB The output voltage Vout of the output circuit 12 is a first specific value.

[0049] When the current required by the external load increases, it will cause the second feedback voltage V to rise. OCP_FB Rise until the reference voltage Vref and the first feedback voltage V FB The second feedback voltage is equal to V OCP_FB At this time, in order to avoid excessive output current (overcurrent), the first stage of the internal start-up current step-back protection of the low dropout linear regulator 2 limits the output current of the output circuit 12 to a second specific value.

[0050] When the current required by the external load rises, it is equivalent to the resistance of the external load dropping, and the output voltage Vout of the equivalent output circuit 12 becomes smaller, which causes the first feedback voltage V FB to drop, and the first feedback voltage V FB becomes smaller than the second feedback voltage V OCP_FB . The current step-back protection circuit 1 outputs the second feedback voltage V OCP_FB through the current feedback circuit 13, and the second feedback voltage V OCP_FB takes effect, completely taking over the internal circuit of the low-dropout linear regulator 2 and performing the second phase of current step-back protection on the low-dropout linear regulator 2, so that the output current (the output current of the output circuit 12) of the low-dropout linear regulator 2 is limited to a third specific value.

[0051] The current step-back protection circuit 1 provided in the application participates in the current step-back protection process of the low-dropout linear regulator 2, limits the output current of the output circuit 12 multiple times, avoids the situation that the output current is too large and causes damage to the circuit device, realizes multiple protection of the circuit, improves the safety of the low-dropout linear regulator 2, and improves the safety of the subsequent circuit connected to the low-dropout linear regulator 2.

[0052] The reference voltage Vref mainly provides a constant reference voltage for the output circuit 12 to further control the output voltage value or the output current value of the output circuit 12. The first feedback voltage V FB is a feedback signal of the output circuit 12 and is a feedback mechanism in the low-dropout linear regulator 2, which is used to reflect and control the voltage output of the output circuit 12. The second feedback voltage V OCP_FB is an overcurrent protection feedback signal of the output circuit 12, which is used to detect the output current of the output circuit 12, limit the maximum value of the output current of the output circuit 12, and realize protection of the circuit system.

[0053] The current step-back protection circuit 1 provided in the application is applied to the low-dropout linear regulator 2, so that the low-dropout linear regulator 2 can realize current step-back protection without setting high-power consumption devices such as voltage comparators, realizes the current step-back protection function at a low cost, reduces the implementation power consumption of the overall circuit in the low-dropout linear regulator 2, simplifies the implementation scheme of the current step-back function in the low-dropout linear regulator 2, and improves the practicability of the current step-back protection circuit 1.

[0054] The output circuit 12 can also be connected to a load capacitor CL and a load resistor RL (that is, the external load as described above) respectively. The load capacitor CL mainly serves as the load capacitor of the LDO, and the load resistor RL mainly serves as the load of the equivalent LDO and can be equivalent to the impedance of the entire load.

[0055] In an embodiment, the low-dropout linear regulator 2 further comprises a voltage buffer circuit 15 arranged between the operational amplifier 11 and the output circuit 12, wherein the voltage buffer circuit 15 can comprise a buffer composed of a source follower or the like structure, for isolating the high output impedance of the operational amplifier and the high parasitic capacitance of the power transistor, and improving the stability of the low-dropout linear regulator 2.

[0056] Optionally, the current step foldback protection circuit 1 comprises a first transistor Q1, a current source I, and a flip-flop F, wherein the first input end of the first transistor Q1 is connected with the output circuit 12, the second input end of the first transistor Q1 is connected with the voltage dividing circuit 14, the output end of the first transistor Q1 is connected with the first end of the current source I, the second end of the current source I is grounded, the first end of the current source is connected with the first end of the flip-flop F, and the second end of the flip-flop F is connected with the current feedback circuit 13, wherein the flip-flop F can comprise a first inverter F1 and a second inverter F2 connected in series, and the first transistor Q1 can be a PMOS (P-Metal-Oxide-Semiconductor) transistor.

[0057] The first transistor Q1 is configured to detect the voltage change on the voltage dividing circuit 14 and output a current to the current source I based on the voltage change on the voltage dividing circuit 14, and the flip-flop F is configured to output a circuit signal (the circuit signal can comprise a high-level signal and a low-level signal) to the current feedback circuit 13 based on the current output by the first transistor Q1 and the current of the current source I, and control the second feedback voltage V OCP_FB .

[0058] Specifically, the first transistor Q1 is configured to detect the voltage change on the voltage dividing circuit 14, and the voltage dividing circuit 14 is configured to divide the output voltage Vout, so that the first transistor Q1 can actually detect the voltage change of the output voltage Vout and output a current according to the voltage change of the output voltage Vout. Therefore, the size of the output voltage Vout of the output circuit 12 can be determined by the size of the output current of the first transistor Q1.

[0059] Further, the current source I is mainly configured to provide a reference current for the current step foldback protection circuit 1 and form a current source load single-ended common-source amplifier with the first transistor Q1 to realize the current step foldback function, wherein the size of the current output by the current source I can be set by the user according to the requirements, and the present application does not make any settings. The flip-flop F can be a Schmitt trigger, which is mainly a circuit structure with hysteresis characteristics, and uses different rising threshold and falling threshold to avoid false triggering caused by internal noise of the circuit system.

[0060] When the output current of the first transistor Q1 is greater than the reference current, the flip-flop F can receive a high level signal, and the circuit signal output by the flip-flop F to the current feedback circuit 13 is a high level signal; when the output current of the first transistor Q1 is less than the reference current, the end of the flip-flop F connected with the current source I is pulled down to the ground, that is, the flip-flop F inputs a low level signal, and the circuit signal output by the flip-flop F to the current feedback circuit 13 is a low level signal, and the second feedback voltage V OCP_FB is controlled.

[0061] In summary, by the cooperation of the devices in the current step-back protection circuit 1, the size change of the output voltage Vout of the output circuit 12 can be determined, and the feedback signal is controlled, without setting a high energy consumption circuit such as a comparator, so that the circuit cost and power consumption are reduced, and the implementation scheme of the current step-back function in the low dropout linear regulator 2 is simplified.

[0062] Optionally, the voltage dividing circuit 14 includes a first resistor R1, a second resistor R2 and a third resistor R3, and the first resistor R1, the second resistor R2 and the third resistor R3 form a resistor voltage dividing network to provide an output voltage dividing feedback voltage for the current step-back protection circuit 1 and the operational amplifier 11.

[0063] The first end of the first resistor R1 is connected with the output circuit 12, the second end of the first resistor R1 is connected with the first end of the third resistor R3 through the second resistor R2, the second end of the third resistor R3 is grounded, the second end of the first resistor R1 is connected with the second input end of the first transistor Q1, and the first end of the third resistor R3 is connected with the second input end of the operational amplifier 11, so as to output the first feedback voltage V FB to the operational amplifier 11. OCP_FB .

[0064] The voltage difference between the second input end and the first input end of the first transistor Q1 determines the state of the first transistor Q1 and the current size of the output end of the first transistor Q1, the first input end of the first transistor Q1 is connected with the first end of the first resistor R1, and the second input end of the first transistor Q1 is connected with the second end of the first resistor R1, that is, the voltage difference between the second input end and the first input end of the first transistor Q1 is equal to the voltage drop on the first resistor R1. Therefore, the voltage drop on the first resistor R1 will affect the output current of the first transistor Q1, and then affect the second feedback voltage V OCP_FB .

[0065] Wherein, since the first end of the first resistor R1 is connected with the output circuit 12, and the second end of the third resistor R3 is grounded, the sum of the voltage drop on the first resistor R1, the voltage drop on the second resistor R2 and the voltage drop on the third resistor R3 is equal to the output voltage Vout of the output circuit 12. The first feedback voltage V FB is equal to the voltage drop on the third resistor R3, and the second feedback voltage V FB is equal to the voltage drop on the second resistor R2. The output voltage Vout can be fed back. And the voltage drop on the first resistor R1 can also represent the output voltage Vout. The current step-back protection circuit 1 can determine the size of the output voltage Vout and the threshold voltage V foldback , and then adjust the second feedback voltage V OCP_FB output by the current feedback circuit 13.

[0066] Optionally, the current feedback circuit 13 comprises a second transistor Q2, a third transistor Q3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6 and a seventh resistor R7. Wherein, the second transistor Q2 and the third transistor Q3 can be NMOS (N-Metal-Oxide-Semiconductor) transistors, which are used as switching tubes to control the equivalent impedance size of the output current conversion voltage of the detection output circuit 12, and further realize the current step-back protection in the low-dropout linear regulator 2.

[0067] The first input end of the second transistor Q2 is connected with the output circuit 12 through the fourth resistor R4, the second input end of the second transistor Q2 is connected with the second input end of the third transistor Q3, the output end of the second transistor Q2 is grounded, the first input end of the third transistor Q3 is connected with the output circuit 12 through the sixth resistor R6, the second input end of the third transistor Q3 is connected with the second end of the flip-flop F, and the output end of the third transistor Q3 is grounded. The first end of the fifth resistor R5 is connected with the first end of the fourth resistor R4, the second end of the fifth resistor R5 is grounded, the first end of the seventh resistor R7 is connected with the first end of the sixth resistor R6, the second end of the seventh resistor R7 is grounded, and the first end of the fifth resistor R5 is connected with the third input end of the operational amplifier 11.

[0068] Wherein, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6 and the seventh resistor R7 are current sampling resistors, which mainly convert the detected output current into voltage and output an equivalent voltage signal (i.e. the second feedback signal V OCP_FB ). In an embodiment, the resistance value of the fourth resistor R4 can be equal to the resistance value of the sixth resistor R6, and the resistance value of the fifth resistor R5 can be equal to the resistance value of the seventh resistor R7.

[0069] Specifically, when the output voltage Vout of the output circuit 12 is greater than the threshold voltage Vfoldback When the output current of the first transistor Q1 is greater than the reference current of the current source I, that is, when the flip-flop F outputs a high level signal, the second transistor Q2 and the third transistor Q3 are turned on, at this time, the fourth resistor R4 and the fifth resistor R5 are connected in parallel, and the first end of the fourth resistor R4 and the fifth resistor R5 outputs the second feedback voltage V OCP_FB .

[0070] When the output voltage Vout of the output circuit 12 is less than the threshold voltage V foldback , the first transistor Q1 is less than the reference current of the current source I, the flip-flop F outputs a low level signal, the second transistor Q2 and the third transistor Q3 are cut off, and then the fourth resistor R4 is disconnected, and only the first end of the fifth resistor R5 outputs the second feedback voltage V OCP_FB .

[0071] The embodiment is based on the comparison result of the output voltage Vout and the threshold voltage V foldback , to control the conduction of the second transistor Q2 and the third transistor Q3 in the current feedback circuit 13, so as to change the equivalent impedance in the current feedback circuit 13, and then change the size of the second feedback voltage V OCP_FB . OCP_FB .

[0072] Optionally, the output circuit 12 comprises a fourth transistor Q4, a fifth transistor Q5, a sixth transistor Q6 and a seventh transistor Q7, wherein the fourth transistor Q4 and the fifth transistor Q5 can be PLDMOS (P-type Lateral Diffused Metal Oxide Semiconductor), and the fifth transistor Q5 and the sixth transistor Q6 can be PMOS.

[0073] Specifically, the first input terminals of the fourth transistor Q4 and the fifth transistor Q5 are connected to the power supply Vin, the second input terminals of the fourth transistor Q4 and the fifth transistor Q5 are connected to the output terminals of the operational amplifier 11, the output terminal of the fourth transistor Q4 is connected to the first input terminal of the sixth transistor Q6, the second input terminal of the sixth transistor Q6 is connected to the second input terminal of the seventh transistor Q7, the output terminals of the sixth transistor Q6 and the seventh transistor Q7 are connected to the current feedback circuit 13. Specifically, the output terminal of the sixth transistor Q6 is connected to the first input terminal of the third transistor Q3 through the sixth resistor R6, the output terminal of the seventh transistor Q7 is connected to the first input terminal of the second transistor Q2 through the fourth resistor R4, the second input terminal of the seventh transistor Q7 is connected to the output terminal of the seventh transistor Q7, and the output terminal of the fourth transistor Q4 is connected to the current step foldback protection circuit 1 and the voltage divider circuit 14. Specifically, the output terminal of the fourth transistor Q4 is also connected to the first input terminal of the first transistor Q1 and the first terminal of the first resistor R1.

[0074] Specifically, the fourth transistor Q4 and the fifth transistor Q5 form a current mirror, and the sixth transistor Q6 and the seventh transistor Q7 also form a current mirror. The fourth transistor Q4 is used to provide the output voltage Vout and output current of the output circuit 12, while the fifth transistor Q5 is used to detect the output current of the output circuit 12. The output current of the fourth transistor Q4 can be greater than the output current of the fifth transistor Q5. In one embodiment, the ratio between the output current of the fourth transistor Q4 and the output current of the fifth transistor Q5 is n, where n is a natural number much greater than 1. It is understood that this application does not limit the specific value of n and can be set by the user based on actual needs.

[0075] The current mirror composed of the sixth transistor Q6 and the seventh transistor Q7 is used to control the drain voltages of the fourth transistor Q4 and the fifth transistor Q5 to be equal, so as to ensure the mirror accuracy of the fifth transistor Q5. The output current of the sixth transistor Q6 can be equal to the output current of the seventh transistor Q7.

[0076] Furthermore, the electrical parameters of the low-dropout linear regulator 2 are described in detail below:

[0077] In one embodiment, at the first feedback voltage V FB Greater than the second feedback voltage V OCP_FB At this time, that is, the low-dropout linear regulator 2 is operating normally and the current step foldback protection is not triggered. At this time, the operational amplifier 11 is based on the first feedback voltage V FB The output circuit 12 is controlled, and the set output voltage V of the low dropout linear regulator 2 is set. Oset (The set output voltage V of output circuit 12)Oset , i.e. the first specific value as mentioned above) is the product of the reference voltage Vref and a first coefficient, the first coefficient being equal to the sum of the resistance value of the first resistor R1, the resistance value of the second resistor R2 and the resistance value of the third resistor R3 divided by the resistance value of the third resistor R3. Wherein, the set output voltage V Oset of the low-dropout linear regulator 2 is the output voltage of the low-dropout linear regulator 2 when the low-dropout linear regulator 2 is in normal operation.

[0078] Specifically, the set output voltage V Oset may be represented as:

[0079]

[0080] Wherein, Vref is the reference voltage, R1 is the resistance value of the first resistor R1, R2 is the resistance value of the second resistor R2, and R3 is the resistance value of the third resistor R3.

[0081] The size of the voltage output by the output circuit 12 when the low-dropout linear regulator 2 is in normal operation can be obtained by formula (1).

[0082] Further, if the required current of the load RL (the equivalent current required on the load resistor RL when the low-dropout linear regulator 2 is in normal operation) rises, the second feedback voltage V OCP_FB output by the current feedback circuit 13 will rise accordingly, until the second feedback voltage V OCP_FB is equal to the reference voltage Vref, triggering the first stage of the current step-back protection to limit the output current of the output circuit 12, at which time the output voltage Vout of the output circuit 12 drops, and the first feedback voltage V FB is less than or equal to the second feedback voltage V OCP_FB , the operational amplifier 11 can control the output of the output circuit 12 based on the second feedback voltage V OCP_FB , and at this time, the output voltage Vout of the low-dropout linear regulator 2 is greater than the threshold voltage V foldback . At this time, the output current of the low-dropout linear regulator 2 is limited to the first output current I OCP1 , i.e. the second specific value as mentioned above, the first output current I OCP1 is the product of the reference voltage Vref and a second coefficient, divided by the resistance value of the fifth resistor R5 and the fourth resistor R4 in parallel, and the second coefficient is the ratio of the output current of the fourth transistor Q4 and the output current of the fifth transistor Q5.

[0083] Specifically, the first output current I OCP1 may be represented as:

[0084]

[0085] Wherein, n is the ratio of the output current of the fourth transistor Q4 and the output current of the fifth transistor Q5, and R4||R5 is the equivalent resistance of the fourth resistor R4 and the fifth resistor R5 in parallel.

[0086] Wherein, as described above, the second feedback voltage V OCP_FB is greater than or equal to the first feedback voltage V FB , and the output voltage Vout of the output circuit 12 is greater than the threshold voltage V foldback , the current step-back protection circuit 1 outputs a high voltage to the current feedback circuit 13, the second transistor Q2 and the third transistor Q3 are turned on, and the fourth resistor R4 and the fifth resistor R5 are in parallel, at this time, the output current of the low dropout linear regulator 2 is limited to the first output current I OCP1 .

[0087] Wherein, the threshold voltage V foldback may be equal to the product of the voltage difference between the first input and the second input of the first transistor Q1 and the third coefficient, wherein the third coefficient is the sum of the resistance value of the first resistor R1, the resistance value of the second resistor R2 and the resistance value of the third resistor R3 divided by the resistance value of the first resistor R1.

[0088] The specific derivation process can be:

[0089] The overdrive voltage of the first voltage is:

[0090]

[0091] Wherein, I is the current of the current source I, and gm is the transconductance of the first transistor Q1, which is used to describe the ability of the source voltage of the first transistor Q1 to control the current.

[0092] Further, as described above, the voltage difference between the first input and the second input of the first transistor Q1 is equal to the voltage drop across the first resistor R1, and the voltage difference between the first input and the second input of the first transistor Q1 can be represented as:

[0093] V gs = V over-drive + V th = V R1 (4)

[0094] Wherein, Vth is the threshold voltage of the first transistor Q1, defined as the minimum gate bias voltage that can form a conductive channel between the source and the drain, here used to describe the minimum gate-source voltage for the first transistor Q1 to turn on, and V R1 is the voltage drop across the first resistor R1.

[0095] Further, the threshold voltage V foldback may be represented as:

[0096]

[0097] Then, based on the output voltage Vout of output circuit 12 and the threshold voltage V, foldback The relationship between these factors further limits the output current of output circuit 12.

[0098] In another embodiment, if the external load continues to increase, causing the output voltage Vout of the output circuit 12 to continuously decrease until the first feedback voltage V FB Less than or equal to the second feedback voltage V OCP_FB Furthermore, the output voltage Vout of the low-dropout linear regulator 2 is less than the threshold voltage V. foldback When this occurs, the second stage of the current step-back protection is triggered, and the output current of the low-dropout linear regulator 2 is limited to the second output current I. OCP2 That is, the third characteristic value mentioned above, the second output current I. OCP2 The first output current I OCP1 The product of the fourth coefficient and the fifth coefficient is equal to the resistance of the fourth resistor R4 divided by the sum of the resistance of the fourth resistor R4 and the resistance of the fifth resistor R5.

[0099] As mentioned earlier, the first feedback voltage V FB Less than or equal to the second feedback voltage V OCP_FB And the output voltage Vout of output circuit 12 is less than the threshold voltage V foldback When the current step back protection circuit 1 outputs a low level to the current feedback circuit 13, the second transistor Q2 and the third transistor Q3 are cut off. At this time, the current sampling resistor is switched from the fourth resistor R4 and the fifth resistor R5 in parallel to the fifth resistor R5. The output current of the output circuit 12 will be reduced to a lower second output current I. OCP2 This is to avoid thermal damage to the output power transistor.

[0100] Among them, the second output current I OCP2 It can be represented as:

[0101]

[0102] The following is a summary of the operation of the low-dropout linear regulator 2:

[0103] First feedback voltage V FB Greater than the second feedback voltage V OCP_FB When the low-dropout linear regulator 2 is operating normally and the voltage foldback protection is not triggered, the output circuit 12 will operate at the set output voltage V. Oset Output.

[0104] First feedback voltage V FB Less than or equal to the second feedback voltage VOCP_FB , and the output voltage Vout of the output circuit 12 is greater than the threshold voltage V foldback , the first stage of the current step-back protection is triggered, and the output current of the output circuit 12 is limited to the first output current I OCP1 .

[0105] When the first feedback voltage V FB is less than or equal to the second feedback voltage V OCP_FB , and the output voltage Vout of the output circuit 12 is less than the threshold voltage V foldback , the second stage of the current step-back protection is triggered, and the output current of the output circuit 12 is further limited to the second output current I OCP2 .

[0106] Optionally, please continue to refer to Figure 3 , Figure 3 is Figure 2 the operating IV characteristic diagram of the low dropout linear regulator 2. When the output voltage Vout of the output circuit 12 is less than the threshold voltage V foldback , the output current of the output circuit 12 is limited to the second output current I OCP2 , and when the output voltage Vout of the output circuit 12 is less than the set output voltage V Oset , and greater than the threshold voltage V foldback , the output current of the output circuit 12 is limited to the first output current I OCP1 .

[0107] In summary, the current step-back protection circuit 1 provided by the present application is applied to the low dropout linear regulator 2, cooperates with the operational amplifier 11, the output circuit 12, the voltage dividing circuit 14 and the current feedback circuit 13 in the low dropout linear regulator 2, and uses the resistance string voltage division of the voltage dividing circuit 14 and the single-stage current source load common-source MOS tube amplification circuit of the current step-back protection circuit 1 to make the equivalent step-back protection threshold voltage V foldback can be flexibly set, multiple limitations on the output current of the low dropout linear regulator 2 are achieved, loss caused by overcurrent is avoided, circuit complexity caused by using a double-ended comparator is avoided, implementation cost and power consumption are reduced, multiple protections of the circuit are achieved, the purpose of applying the current step-back protection to the low-power scenario of the low dropout linear regulator 2 is achieved, and the practicability of the current step-back protection circuit 1 provided by the present application is improved.

[0108] The above description is only an embodiment of the present application, and does not limit the patent scope of the present application, and any equivalent structure or equivalent flow transformation using the content of the specification and the drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A current step-back protection circuit, characterized in that, It is applied to low dropout linear regulators, which include operational amplifiers, output circuits, current feedback circuits, and voltage divider circuits; The first input terminal of the current step back protection circuit is connected to the output circuit, and the second input terminal of the current step back protection circuit is connected to the voltage divider circuit. The voltage divider circuit is connected to the first input terminal of the operational amplifier, and the output terminal of the current step foldback protection circuit is connected to the second input terminal of the operational amplifier through the current feedback circuit; The operational amplifier's third input terminal is used to receive a reference voltage, the operational amplifier's output terminal is connected to the output circuit, and the output circuit is connected to the current feedback circuit and the voltage divider circuit. The voltage divider circuit is used to output a first feedback voltage to the operational amplifier, the current step foldback protection circuit is used to output a second feedback voltage to the operational amplifier through the current feedback circuit, and the operational amplifier is used to control the output parameters of the output circuit based on the first feedback voltage and the second feedback voltage.

2. The current step-back protection circuit according to claim 1, characterized in that, The current step-back protection circuit includes a first transistor, a current source, and a trigger. The first input terminal of the first transistor is connected to the output circuit, the second input terminal of the first transistor is connected to the voltage divider circuit, the output terminal of the first transistor is connected to the first terminal of the current source, the second terminal of the current source is grounded, the first terminal of the current source is connected to the first terminal of the flip-flop, and the second terminal of the flip-flop is connected to the current feedback circuit. The first transistor is used to detect the voltage change of the voltage divider circuit and output current to the current source based on the voltage change of the voltage divider circuit. The trigger is used to output a circuit signal to the current feedback circuit based on the current output by the first transistor and the current of the current source, so as to control the second feedback voltage output by the current feedback circuit to the operational amplifier.

3. The current step-back protection circuit according to claim 2, characterized in that, The voltage divider circuit includes a first resistor, a second resistor, and a third resistor. The first end of the first resistor is connected to the output circuit. The second end of the first resistor is connected to the first end of the third resistor through the second resistor. The second end of the third resistor is grounded. The second end of the first resistor is connected to the second input terminal of the first transistor. The first end of the third resistor is connected to the second input terminal of the operational amplifier, and is used to output the first feedback voltage to the operational amplifier. The first transistor is used to output current based on the voltage drop across the first resistor in order to control the second feedback voltage output by the current feedback circuit to the operational amplifier.

4. The current step-back protection circuit according to claim 3, characterized in that, The current feedback circuit includes a second transistor, a third transistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor; The first input terminal of the second transistor is connected to the output circuit through the fourth resistor, the second input terminal of the second transistor is connected to the second input terminal of the third transistor, and the output terminal of the second transistor is grounded; the first input terminal of the third transistor is connected to the output circuit through the sixth resistor, the second input terminal of the third transistor is connected to the second terminal of the flip-flop, and the output terminal of the third transistor is grounded. The first end of the fifth resistor is connected to the first end of the fourth resistor, the second end of the fifth resistor is grounded, the first end of the seventh resistor is connected to the first end of the sixth resistor, and the second end of the seventh resistor is grounded. The first terminal of the fifth resistor is connected to the third input terminal of the operational amplifier.

5. The current step-back protection circuit according to claim 4, characterized in that, The output circuit includes a fourth transistor, a fifth transistor, a sixth transistor, and a seventh transistor. The first input terminals of the fourth transistor and the fifth transistor are respectively connected to a power supply. The second input terminals of the fourth transistor and the fifth transistor are respectively connected to the output terminals of the operational amplifier. The output terminal of the fourth transistor is connected to the first input terminal of the sixth transistor. The output terminal of the fifth transistor is connected to the first input terminal of the seventh transistor. The second input terminal of the sixth transistor is connected to the second input terminal of the seventh transistor. The output terminals of the sixth transistor and the seventh transistor are respectively connected to the current feedback circuit. The second input terminal of the seventh transistor is connected to the output terminal of the seventh transistor. The output terminal of the fourth transistor is connected to the current step back protection circuit and the voltage divider circuit.

6. The current step-back protection circuit according to claim 5, characterized in that, The output current of the fourth transistor is greater than the output current of the fifth transistor, and the output current of the sixth transistor is equal to the output current of the seventh transistor.

7. The current step-back protection circuit according to claim 5, characterized in that, When the first feedback voltage is greater than the second feedback voltage, the set output voltage of the low dropout linear regulator is the product of the reference voltage and the first coefficient, where the first coefficient is equal to the sum of the resistance values ​​of the first resistor, the second resistor, and the third resistor divided by the resistance value of the third resistor.

8. The current step-back protection circuit according to claim 5, characterized in that, When the first feedback voltage is less than or equal to the second feedback voltage and the output voltage of the low-dropout linear regulator is greater than the threshold voltage, the output current of the low-dropout linear regulator is limited to a first output current. The first output current is equal to the product of the reference voltage and the second coefficient, divided by the resistance value of the fifth resistor and the fourth resistor connected in parallel. The second coefficient is the ratio of the output current of the fourth transistor to the output current of the fifth transistor.

9. The current step-back protection circuit according to claim 8, characterized in that, The threshold voltage is equal to the product of the voltage difference between the first and second input terminals of the first transistor and the third coefficient; The third coefficient is the sum of the resistance values ​​of the first resistor, the second resistor, and the third resistor, divided by the resistance value of the first resistor.

10. The current step-back protection circuit according to claim 8, characterized in that, When the first feedback voltage is less than or equal to the second feedback voltage, and the output voltage of the low-dropout linear regulator is less than the threshold voltage, the output current of the low-dropout linear regulator is limited to a second output current. The second output current is equal to the product of the first output current and a fourth coefficient. The fourth coefficient is equal to the resistance value of the fourth resistor divided by the sum of the resistance values ​​of the fourth resistor and the fifth resistor.

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