A current step-back protection circuit

Abstract

This application discloses a current-step foldback protection circuit. This circuit is applied to low-dropout linear regulators (LDLs), enabling current-step foldback protection without the need for high-power devices such as voltage comparators. This reduces the cost of implementing current-step foldback protection in LDLs. While controlling the output current, it also reduces power consumption in the circuit, further enabling the application of current-step foldback protection technology to low-power scenarios in LDLs. This reduces the operating power consumption of LDLs with current-step foldback protection and simplifies the implementation scheme for current-step foldback protection in LDLs.

Description

Technical Field

[0001] This application relates to the field of current step-back technology, and in particular to a current step-back protection circuit. Background Technology

[0002] In the use of LDOs (Low Dropout Regulators) with current step foldback protection, current protection can effectively prevent damage to the device caused by excessive load current. Current step foldback protection is a common overcurrent protection function that reduces the output current based on the output voltage, preventing thermal damage to the output power transistor and protecting the entire circuit system, further ensuring stable system operation.

[0003] Currently, LDO structures with current-step foldback protection typically include voltage comparator circuits, current comparator circuits, and current-limiting circuits. The circuit module implementing current-step foldback protection is generally the voltage comparator circuit, which contains one or more comparators to compare and determine whether the output voltage is lower than a threshold. This causes the reference current in the current comparator circuit to be reduced, controlling the current-limiting circuit to limit the current output of the LDO, thus completing the current-step foldback protection function. However, traditional current-step foldback protection structures are overly complex and costly, and also increase the normal operating power consumption of the LDO, making this technology difficult to apply to low-power applications. Utility Model Content

[0004] To solve the above-mentioned technical problems, this application provides a current step-back protection circuit for use in a low-dropout linear regulator, wherein the low-dropout linear regulator includes an operational amplifier, an output circuit, a current feedback circuit, and a voltage divider circuit.

[0005] 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.

[0006] 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;

[0007] 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.

[0008] 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.

[0009] The current step-back protection circuit includes a first transistor, a current source, and a trigger.

[0010] 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.

[0011] 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.

[0012] 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, and 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, and the first end of the third resistor is connected to the second input terminal of the operational amplifier, for outputting the first feedback voltage to the operational amplifier.

[0013] 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.

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

[0015] The first input terminal of the second transistor is connected to the output circuit through the fifth 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.

[0016] 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.

[0017] The first terminal of the fifth resistor is connected to the third input terminal of the operational amplifier.

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

[0019] 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.

[0020] The output terminal of the fourth transistor is connected to the current step back protection circuit and the voltage divider circuit.

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

[0022] The beneficial effects of this application are as follows: Unlike existing technologies, the current-stepping foldback protection circuit provided in this application is applied to low-dropout linear regulators (LDLs) for current-stepping foldback protection. The LDL includes an operational amplifier, an output circuit, a current feedback circuit, and a voltage divider circuit. The first input terminal of the current-stepping foldback protection circuit is connected to the output circuit, and the second input terminal 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 is connected to the second input terminal of the operational amplifier via the current feedback circuit. The operational amplifier receives a reference voltage, a first feedback voltage transmitted by the voltage divider circuit, and a second feedback voltage transmitted by the current-stepping foldback protection circuit through the current feedback circuit. Based on the first and second feedback voltages, it controls the output current of the output circuit to achieve stepping foldback protection for the LDL, thereby improving the operational safety of the LDL. The current step back protection circuit provided in this application is applied to low dropout linear regulators, enabling current step back protection to be implemented in low dropout linear regulators without the need for high-power devices such as voltage comparators. This reduces the cost of implementing current step back protection in low dropout linear regulators. While controlling the output current, it also reduces power consumption in the circuit, further enabling the application of current step back protection technology to low-power scenarios of low dropout linear regulators. This simplifies the implementation scheme for users to implement current step back protection function in low dropout linear regulators. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] in:

[0025] Figure 1 This is a schematic diagram of an embodiment of an existing low-dropout linear regulator with current step-back protection;

[0026] Figure 2 This is a schematic diagram of an embodiment of the current step-back protection circuit and the low dropout linear regulator provided in this application;

[0027] Figure 3 yes Figure 2 IV characteristic diagram of a medium-low differential voltage linear regulator.

[0028] Reference numerals: 1. Current step-back protection circuit; 2. Low dropout linear regulator; 11. Operational amplifier; 12. Output circuit; 13. Current feedback circuit; 14. Voltage divider circuit; 15. Voltage buffer circuit. Detailed Implementation

[0029] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0030] In the following description, specific details such as particular system architectures, interfaces, and technologies are presented for illustrative purposes rather than for limiting purposes, in order to provide a thorough understanding of this application.

[0031] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " generally indicates that the preceding and following related objects are in an "or" relationship. Furthermore, "many" in this application means two or more. Moreover, the term "at least one" in this application means any combination of at least two of any one or more of a plurality of objects. 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. Furthermore, the terms "first," "second," and "third" in this application are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0033] Existing LDOs with current step-back protection function are generally like... Figure 1 As shown, the main circuit module implementing the current-step foldback protection function is the voltage comparator circuit. Internally, it contains one or more comparators to compare the output voltage with a voltage threshold, thereby lowering the reference current in the current comparator circuit. This controls the current-limiting circuit to limit the current output of the LDO, thus completing the current-step foldback protection function. However, traditional current-step foldback protection structures are overly complex and costly to implement, and they also increase the normal operating power consumption of the LDO, making this technology difficult to apply to low-power applications.

[0034] This application provides a current step-back protection circuit. By combining a resistor series voltage divider and a single-stage current source load common-source MOSFET amplifier circuit, the equivalent back-back protection threshold voltage can be flexibly set, thereby avoiding the circuit complexity caused by using a dual-ended comparator and reducing its implementation cost and power consumption in low-dropout linear regulators.

[0035] For details, please refer to Figure 2 The current step back protection circuit 1 provided in this application is applied to the low-dropout linear regulator 2 and participates in the circuit back-back protection process of the low-dropout linear regulator 2. It is understood that the current step back protection circuit 1 provided in this application can also participate in the current step back protection process in other circuit modules that require current step back protection function.

[0036] The following describes in detail the current step-back protection circuit 1 provided in this application, taking into account the structure of the low-dropout linear regulator 2:

[0037] The low dropout linear regulator 2 includes an operational amplifier 11, an output circuit 12, a current feedback circuit 13, and a voltage divider circuit 14.

[0038] The first input terminal of the current step back protection circuit 1 is connected to the output circuit 12, the second input terminal of the current step back protection circuit is connected to the voltage divider circuit, the voltage divider circuit 14 is connected to the first input terminal of the operational amplifier 11, and the current step back protection circuit 1 is connected to the second input terminal of the operational amplifier 11 through the current feedback circuit 13.

[0039] The third input terminal of the operational amplifier 11 is used to receive the reference voltage Vref. The output terminal of the operational amplifier 11 is connected to the output circuit 12, which is also connected to the current feedback circuit 13 and the voltage divider circuit 14.

[0040] Voltage divider circuit 14 is used to output the first feedback voltage V to operational amplifier 11. FB The current step-back protection circuit 1, through the current feedback circuit 13, is used to output the second feedback voltage V to the operational amplifier 11. OCP_FB Operational amplifier 11 is used based on the first feedback voltage V FB Second 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.

[0041] Specifically, such as Figure 2As 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.

[0042] 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-back 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.

[0043] 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.

[0044] 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.

[0045] When the current required by the external load increases, it can be equivalent to a decrease in the resistance of the external load. Therefore, the output voltage Vout of the equivalent output circuit 12 decreases, which leads to a decrease in the first feedback voltage V. FB The first feedback voltage V drops. FB Less than the second feedback voltage V OCP_FB The current step-back protection circuit 1 outputs a second feedback voltage V through the current feedback circuit 13. OCP_FB The second feedback voltage V OCP_FBIt takes effect, completely taking over the internal circuit of the low dropout linear regulator 2, and performing the second stage of current step back protection on the low dropout linear regulator 2. The output current of the low dropout linear regulator 2 (the output current of the output circuit 12) is limited to a third specific value.

[0046] The current step-back protection circuit 1 provided in this application participates in the current step-back protection process of the low dropout linear regulator 2. By limiting the output current of the output circuit 12 in multiple ways, it avoids the situation where the output current is too large and damages the circuit devices, thereby realizing multiple protections for the circuit, improving the safety of the low dropout linear regulator 2, and improving the safety of subsequent circuits connected to the low dropout linear regulator 2.

[0047] The reference voltage Vref primarily serves to provide a constant reference voltage for the output circuit 12, further controlling the output voltage or current value of the output circuit 12. The first feedback voltage V... FB The feedback signal for output circuit 12 is the feedback mechanism in low-dropout linear regulator 2, used to reflect and control the voltage output of output circuit 12. The second feedback voltage V... OCP_FB This is the overcurrent protection feedback signal for the output circuit 12, used to detect and reflect the output current of the output circuit 12, limit the maximum value of the output current of the output circuit 12, and realize the protection of the circuit system.

[0048] The current step back protection circuit 1 provided in this application is applied to a low dropout linear regulator 2, enabling the low dropout linear regulator 2 to achieve current step back protection without the need for high-power devices such as voltage comparators. This achieves the current step back protection function at a low cost, reduces the overall circuit power consumption 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 practicality of the current step back protection circuit 1.

[0049] The output circuit 12 can also be connected to the load capacitor CL and the load resistor RL (that is, the external load as mentioned above). The load capacitor CL mainly serves as the load capacitor of the LDO, while the load resistor RL mainly serves as the equivalent load of the LDO, which can be equivalent to the impedance of the entire load.

[0050] In one embodiment, the low dropout linear regulator 2 further includes a voltage buffer circuit 15, which is located between the operational amplifier 11 and the output circuit 12. The voltage buffer circuit 15 may include a buffer composed of a source follower or similar structure to isolate the high output impedance of the operational amplifier and the high parasitic capacitance of the power transistor, thereby improving the stability of the low dropout linear regulator 2.

[0051] Optionally, the current step-back protection circuit 1 includes a first transistor Q1, a current source I, and a flip-flop F. The first input terminal of the first transistor Q1 is connected to the output circuit 12, the second input terminal of the first transistor Q1 is connected to the voltage divider circuit 14, the output terminal of the first transistor Q1 is connected to the first terminal of the current source I, the second terminal of the current source I is grounded, the first terminal of the current source I is connected to the first terminal of the flip-flop F, and the second terminal of the flip-flop F is connected to the current feedback circuit 13. The flip-flop F may include a first inverter F1 and a second inverter F2 connected in series. The first transistor Q1 may be a PMOS (P-Metal-Oxide-Semiconductor) transistor.

[0052] In this circuit, the first transistor Q1 detects the voltage change in the voltage divider circuit 14 and outputs current to the current source I based on the voltage change in the voltage divider circuit 14. The trigger F outputs a circuit signal (which may include 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 controls the current feedback circuit 13 to output the second feedback voltage V to the operational amplifier 11. OCP_FB .

[0053] Specifically, the first transistor Q1 is used to detect voltage changes on the voltage divider circuit 14, which in turn divides the output voltage Vout. Therefore, the first transistor Q1 can actually detect voltage changes in the output voltage Vout and output current based on these changes. Thus, the magnitude of the output voltage Vout of the output circuit 12 can be determined by the magnitude of the output current of the first transistor Q1.

[0054] Furthermore, the main function of current source I is to provide a reference current for the current step-back protection circuit 1, forming a current source load unipolar common-source amplifier with the first transistor Q1 to realize the current step-back function. The magnitude of the output current of current source I can be set by the user according to requirements; this application does not provide such setting. The trigger F can be a Schmitt trigger, whose main function is a circuit structure with hysteresis characteristics. It utilizes the difference between the rising and falling thresholds to avoid false triggering caused by internal noise in the circuit system.

[0055] 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 to the current source I is pulled down to ground, that is, the flip-flop F receives 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, affecting the second feedback voltage V output by the current feedback circuit 13. OCP_FB To take control.

[0056] In summary, this application can determine the magnitude change of the output voltage Vout of the output circuit 12 by coordinating the components in the current step foldback protection circuit 1, and then control the feedback signal. There is no need to set up high-energy-consuming circuits such as comparators, which reduces circuit cost and power consumption and simplifies the implementation scheme of the current step foldback function in the low dropout linear regulator 2.

[0057] Optionally, the voltage divider circuit 14 includes a first resistor R1, a second resistor R2, and a third resistor R3. The first resistor R1, the second resistor R2, and the third resistor R3 form a resistor voltage divider network to provide the output voltage divider feedback voltage for the current step foldback protection circuit 1 and the operational amplifier 11.

[0058] In this circuit, the first terminal of the first resistor R1 is connected to the output circuit 12, the second terminal of the first resistor R1 is connected to the first terminal of the third resistor R3 through the second resistor R2, the second terminal of the third resistor R3 is grounded, the second terminal of the first resistor R1 is connected to the second input terminal of the first transistor Q1, and the first terminal of the third resistor R3 is connected to the second input terminal of the operational amplifier 11, for outputting the first feedback voltage V to the operational amplifier 11. FB The current step foldback protection circuit 1 is used to control the second feedback voltage V output by the current feedback circuit 13 to the operational amplifier 11 based on the voltage drop across the first resistor R1. OCP_FB .

[0059] In this circuit, the voltage difference between the second input terminal and the first input terminal of the first transistor Q1 determines the state of the first transistor Q1 and the magnitude of the output current. The first input terminal of the first transistor Q1 is connected to the first terminal of the first resistor R1, and the second input terminal of the first transistor Q1 is connected to the second terminal of the first resistor R1. That is, the voltage difference between the second input terminal and the first input terminal of the first transistor Q1 is equal to the voltage drop across the first resistor R1. Therefore, the voltage drop across the first resistor R1 affects the magnitude of the output current of the first transistor Q1, and consequently affects the second feedback voltage V. OCP_FB .

[0060] Since the first terminal of the first resistor R1 is connected to the output circuit 12, and the second terminal of the third resistor R3 is grounded, the sum of the voltage drops across the first resistor R1, the second resistor R2, and the third resistor R3 equals the output voltage Vout of the output circuit 12. The first feedback voltage V... FB If the voltage drop across the third resistor R3 is equal to the voltage drop across the first feedback voltage V, then the first feedback voltage V FB Feedback can be provided on the output voltage Vout. Furthermore, the voltage drop across the first resistor R1 can also characterize the output voltage Vout. The current step foldback protection circuit 1 can determine the relationship between the output voltage Vout and the threshold voltage V based on the voltage drop across the first resistor R1. foldback The magnitude of the voltage, and consequently the second feedback voltage V output by the current feedback circuit 13. OCP_FB Adjustments will be made.

[0061] Optionally, the current feedback circuit 13 includes 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. The second transistor Q2 and the third transistor Q3 can be NMOS (N-Metal-Oxide-Semiconductor) transistors, serving as switching transistors to control the equivalent impedance of the output current-to-voltage conversion of the detection output circuit 12, further realizing the current step-back protection in the low-dropout linear regulator 2.

[0062] The first input terminal of the second transistor Q2 is connected to the output circuit 12 through the fourth resistor R4. The second input terminal of the second transistor Q2 is connected to the second input terminal of the third transistor Q3. The output terminal of the second transistor Q2 is grounded. The first input terminal of the third transistor Q3 is connected to the output circuit 12 through the sixth resistor R6. The second input terminal of the third transistor Q3 is connected to the second terminal of the flip-flop F. The output terminal of the third transistor Q3 is grounded. The first terminal of the fifth resistor R5 is connected to the first terminal of the fourth resistor R4. The second terminal of the fifth resistor R5 is grounded. The first terminal of the seventh resistor R7 is connected to the first terminal of the sixth resistor R6. The second terminal of the seventh resistor R7 is grounded. The first terminal of the fifth resistor R5 is connected to the third input terminal of the operational amplifier 11.

[0063] Among them, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, and the seventh resistor R7 are current sampling resistors. Their main function is to convert the detected output current into voltage and output an equivalent voltage signal (that is, the second feedback signal V). OCP_FB In one 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.

[0064] Specifically, the output voltage Vout of the output circuit 12 is greater than the threshold voltage V.foldback 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 terminals of the fourth resistor R4 and the fifth resistor R5 output the second feedback voltage V to the third input terminal of the operational amplifier 11. OCP_FB .

[0065] The output voltage Vout of output circuit 12 is less than the threshold voltage V. foldback When the output current of 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, the fourth resistor R4 is open-circuited, and only the first terminal of the fifth resistor R5 outputs the second feedback voltage V to the third input terminal of the operational amplifier 11. OCP_FB .

[0066] This embodiment is based on the output voltage Vout and the threshold voltage V foldback Based on the magnitude comparison result, the conduction status of the second transistor Q2 and the third transistor Q3 in the current feedback circuit 13 is controlled to change the equivalent impedance in the current feedback circuit 13, thereby changing the second feedback voltage V. OCP_FB The size of the current step foldback protection circuit 1 is implemented. Based on the change of the output voltage Vout of the output circuit 12, the current feedback circuit 13 controls the second feedback voltage V output to the operational amplifier 11. OCP_FB .

[0067] Optionally, the output circuit 12 includes 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 transistors.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] Furthermore, the electrical parameters of the low-dropout linear regulator 2 are described in detail below:

[0072] 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 The first specific value (as mentioned above) is the product of the reference voltage Vref and the first coefficient. The first coefficient is equal to the sum of the resistance values ​​of the first resistor R1, the second resistor R2, and the third resistor R3, divided by the resistance value of the third resistor R3. The set output voltage Vref of the low-dropout linear regulator 2 is... Oset That is, the output voltage of the low-dropout linear regulator 2 during normal operation.

[0073] Specifically, set the output voltage V Oset It can be represented as:

[0074]

[0075] Where Vref is the reference voltage, R1 is the resistance of the first resistor R1, R2 is the resistance of the second resistor R2, and R3 is the resistance of the third resistor R3.

[0076] The voltage output by the output circuit 12 during normal operation can be calculated using formula (1).

[0077] Furthermore, if the load RL requires an increased current (the equivalent current required across the load resistor RL when the LDO is operating normally), then the second feedback voltage V output by the current feedback circuit 13 will increase. OCP_FB It will rise accordingly, until the second feedback voltage V OCP_FB When the voltage equals the reference voltage Vref, the first stage of the current step-back protection is triggered, limiting the output current of output circuit 12. At this time, the output voltage Vout of output circuit 12 decreases, and the first feedback voltage V... FB Less than or equal to the second feedback voltage V OCP_FB Operational amplifier 11 can be based on the second feedback voltage V OCP_FB The output of output circuit 12 is controlled, and at this time, the output voltage Vout of low dropout linear regulator 2 is greater than the threshold voltage V. foldback The output current of the low-dropout linear regulator 2 is then limited to the first output current I. OCP1 That is, the second specific value mentioned above, the first output current I OCP1 It equals the product of the reference voltage Vref and the second coefficient, divided by the resistance of the fifth resistor R5 and the fourth resistor R4 connected in parallel. The second coefficient is the ratio of the output current of the fourth transistor Q4 to the output current of the fifth transistor Q5.

[0078] Specifically, the first output current I OCP1 It can be represented as:

[0079]

[0080] Where n is the ratio of the output current of the fourth transistor Q4 to 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 connected in parallel.

[0081] As mentioned above, in the second feedback voltage V OCP_FB Greater than or equal to the first feedback voltage V FB Furthermore, the output voltage Vout of output circuit 12 is greater than the threshold voltage V. foldback When 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 connected in parallel. At this time, the output current of the low-dropout linear regulator 2 is limited to the first output current I. OCP1 .

[0082] Among them, the threshold voltage V foldback It can be equal to the product of the voltage difference between the first and second input terminals of the first transistor Q1 and the third coefficient, where the third coefficient is the sum of the resistance values ​​of the first resistor R1, the second resistor R2, and the third resistor R3 divided by the resistance value of the first resistor R1.

[0083] The specific derivation process can be summarized as follows:

[0084] The overdrive voltage of the first voltage is:

[0085]

[0086] Where I is the current of current source I, and gm is the transconductance of the first transistor Q1, which describes the ability of the source voltage of the first transistor Q1 to control the current.

[0087] Furthermore, as can be seen from the preceding text, the voltage difference between the first input terminal and the second input terminal of the first transistor Q1 is equal to the voltage drop across the first resistor R1. Therefore, the voltage difference between the first input terminal and the second input terminal of the first transistor Q1 can be expressed as:

[0088] V gs =V over-drive +V th =V R1 (4)

[0089] Where Vth is the threshold voltage of the first transistor Q1, defined as the minimum gate bias voltage required to form a conductive channel between the source and drain. Here, it describes the minimum gate-source voltage required for the first transistor Q1 to conduct. R1 This is the voltage drop across the first resistor R1.

[0090] Furthermore, the threshold voltage V can be derived. foldback It can be represented as:

[0091]

[0092] 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.

[0093] 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.

[0094] 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.

[0095] Among them, the second output current I OCP2 It can be represented as:

[0096]

[0097] The following is a summary of the operation of the low-dropout linear regulator 2:

[0098] 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.

[0099] First feedback voltage V FB Less than or equal to the second feedback voltage VOCP_FB Furthermore, the output voltage Vout of output circuit 12 is greater than the threshold voltage V. foldback When the first stage of the current step-back protection is triggered, the output current of output circuit 12 is limited to the first output current I. OCP1 .

[0100] 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 second stage of the current step-back protection is triggered, the output current of the output circuit 12 is further limited to the second output current I. OCP2 .

[0101] Alternatively, please continue reading Figure 3 , Figure 3 yes Figure 2 The operating characteristic diagram of the low-to-medium dropout linear regulator 2. When the output voltage Vout of the output circuit 12 is less than the threshold voltage V... foldback At that time, the output current of output circuit 12 is limited to the second output current I. OCP2 However, 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 At that time, the output current of output circuit 12 is limited to the first output current I. OCP1 .

[0102] In summary, the current step foldback protection circuit 1 provided in this application is applied to a low-dropout linear regulator 2. It works in conjunction with the operational amplifier 11, output circuit 12, voltage divider circuit 14, and current feedback circuit 13 in the low-dropout linear regulator 2. By using the resistor series voltage divider of the voltage divider circuit 14 and the single-stage current source load common-source MOSFET amplifier circuit of the current step foldback protection circuit 1, the equivalent foldback protection threshold voltage V is achieved. foldback It can be flexibly configured to achieve multiple limits on the output current of the low dropout linear regulator 2, avoid losses caused by overcurrent, avoid the circuit complexity caused by using a dual-terminal comparator, reduce implementation cost and power consumption, achieve multiple protections for the circuit, and realize the purpose of applying the current step back protection technology to the low power consumption scenario of the low dropout linear regulator 2, thereby improving the practicality of the current step back protection circuit 1 provided in this application.

[0103] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this 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.

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