An LDO without external capacitor

Abstract

The present invention provides an LDO without an external capacitor, wherein a voltage stabilizing unit is used to stabilize a driving voltage received by a control end of a first switch tube within a preset range; a compensation unit is arranged at the output end of the voltage stabilizing unit; the input end of the first switch tube is connected to an external power supply, and the output end of the first switch tube serves as the output end of the LDO without an external capacitor; that is, the compensation unit is arranged at the output end of the voltage stabilizing unit, so that the output voltage of the voltage stabilizing unit is further stabilized within a preset range, and is not affected by the load at the output end, so the stability of the LDO without an external capacitor is also not affected by the output load, thereby improving the load transient response capability of the LDO without an external capacitor; at the same time, the LDO without an external capacitor can reduce the area of ​​its application board for the miniaturization and miniaturization of chips.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic circuits, and more specifically, relates to an LDO without an off-chip capacitor. Background Art

[0002] LDO is widely used in chip circuits because of its stable output voltage and certain noise resistance, providing a stable voltage source for other modules in the chip.

[0003] LDO is divided into LDO with external capacitor and LDO without external capacitor. The general traditional LDO circuit structure is as follows Figure 1 As shown in the figure, the traditional external capacitor type LDO requires an additional pin on the chip for the external capacitor CL, which will increase the design and volume of the PCB board in the application.

[0004] For LDO with external capacitors, for the miniaturization and miniaturization of chips, an external capacitor will undoubtedly increase the area of ​​the application board. For example, with the popularity of wearable devices such as TWS headphones, the design of application boards is becoming more and more miniaturized, and the design of LDO without external capacitors undoubtedly caters to this application demand.

[0005] In addition, for the design without external capacitors in the chip, since there is no external capacitor to maintain the charging and discharging capability of the LDO in response to large loads, its load transient response capability is relatively weak. Summary of the invention

[0006] In view of this, an object of the present invention is to provide a LDO without an external capacitor, so as to improve the load transient response capability of the LDO without an external capacitor.

[0007] The present invention discloses a LDO without an off-chip capacitor, comprising: a voltage stabilizing unit, a first switch tube and a compensation unit;

[0008] The voltage stabilizing unit is used to stabilize the driving voltage received by the control end of the first switch tube within a preset range;

[0009] The compensation unit is arranged at the output end of the voltage stabilizing unit;

[0010] The input end of the first switch tube is used to be connected to an external power supply;

[0011] The output end of the first switch tube serves as the output end of the LDO without an external capacitor.

[0012] Optionally, it also includes: at least one current branch;

[0013] The current branch is used to adjust the current of the first switch tube when the load connected to the output end of the LDO without an off-chip capacitor changes suddenly.

[0014] Optionally, one end of the current branch is connected to the output end of the first switch tube;

[0015] The other end of the current branch is grounded.

[0016] Optionally, the current branch includes: a controllable switch and a current source connected in series.

[0017] Optionally, the current branch includes: a controllable switch and a current mirror connected in series.

[0018] Optionally, the current branch includes: a controllable switch and a resistor connected in series.

[0019] Optionally, the voltage stabilization unit is a bandgap reference circuit.

[0020] Optionally, the voltage stabilizing unit includes: an operational amplifier, a resistor feedback network and a second switch tube;

[0021] The output end of the operational amplifier is connected to the control end of the second switch tube and the control end of the first switch tube respectively;

[0022] The inverting input terminal of the operational amplifier is used to receive a reference voltage;

[0023] The non-inverting input terminal of the operational amplifier is used to receive the output voltage of the resistor feedback network;

[0024] The input end of the second switch tube is connected to the external power supply, and the output end of the second switch tube is connected to one end of the resistor feedback network; the other end of the resistor feedback network is grounded;

[0025] The compensation unit is arranged between the output terminal of the operational amplifier and the ground.

[0026] Optionally, both the first switch tube and the second switch tube are PMOS tubes, or both the first switch tube and the second switch tube are NMOS tubes.

[0027] Optionally, the resistor feedback network includes: a first resistor, a second resistor and a third resistor;

[0028] One end of the first resistor serves as one end of the resistor feedback network;

[0029] The other end of the first resistor is connected to one end of the second resistor;

[0030] The other end of the second resistor is connected to one end of the third resistor, and the voltage at the connection point is used as the output voltage of the resistor feedback network;

[0031] The other end of the third resistor is grounded.

[0032] Optionally, the first resistor is a variable resistor.

[0033] Optionally, the compensation unit is a compensation capacitor;

[0034] The capacitance of the compensation capacitor is within a preset range.

[0035] Optionally, it also includes: load capacitance;

[0036] The load capacitor is arranged between the output end of the first switch tube and the ground.

[0037] It can be seen from the above technical scheme that the present invention provides an LDO without external capacitors, wherein the voltage stabilizing unit is used to stabilize the driving voltage received by the control end of the first switch tube within a preset range; a compensation unit is arranged at the output end of the voltage stabilizing unit; the input end of the first switch tube is connected to the external power supply, and the output end of the first switch tube serves as the output end of the LDO without external capacitors; that is, a compensation unit is arranged at the output end of the voltage stabilizing unit, so as to further stabilize the output voltage of the voltage stabilizing unit within a preset range, which is not affected by the output end load, so the stability of the LDO without external capacitors is also not affected by the output load, thereby improving the load transient response capability of the LDO without external capacitors; at the same time, the LDO without external capacitors reduces the area of ​​its application board for the miniaturization and miniaturization of chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 It is a schematic diagram of a traditional LDO circuit provided by the prior art;

[0040] Figure 2 Schematic diagram of an LDO without external capacitors provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] In this application, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0043] The embodiment of the present invention provides an LDO without an off-chip capacitor, which is used to solve the problem in the prior art that there is no off-chip capacitor to maintain the charging and discharging capability of the LDO for large load response, and therefore, the load transient response capability is weak.

[0044] The LDO without external capacitors, such as Figure 2 As shown, it includes: a voltage stabilizing unit (including Figure 2 OP, MN1, Ract, R1 and R0), the first switch tube MP and the compensation unit Cm.

[0045] The voltage stabilizing unit is used to stabilize the driving voltage received by the control terminal of the first switch tube MP within a preset range.

[0046] Specifically, the output end of the voltage stabilizing unit is connected to the control end of the first switch tube MP; that is, the first switch tube MP is controlled to be on and off by the voltage stabilizing unit. The first switch tube MP is a power MOS tube of an LDO without an external capacitor.

[0047] A compensation unit Cm is arranged at the output end of the voltage stabilizing unit.

[0048] Specifically, the output end of the voltage stabilizing unit is connected to one end of the compensation unit Cm, and the other end of the compensation unit Cm is grounded.

[0049] In practical applications, the compensation unit Cm may be a compensation capacitor, and the capacitance of the compensation capacitor is within a preset range.

[0050] The preset range is not specifically limited here and may be determined based on actual conditions, and is within the protection scope of this application.

[0051] The input end of the first switch tube MP is used to be connected to an external power supply; the output end of the first switch tube MP serves as the output end of the LDO without an off-chip capacitor.

[0052] That is to say, the output voltage of the first switch tube MP is the output voltage of the LDO without an external capacitor; when the output terminal voltage of the voltage stabilizing unit is stable, the control terminal voltage of the first switch tube MP is stable, and thus the output voltage of the LDO without an external capacitor is stable, and it does not change with the load connected to the output terminal LDO_OUT of the LDO without an external capacitor.

[0053] In this embodiment, a compensation unit is provided at the output end of the voltage stabilizing unit to further stabilize the output voltage of the voltage stabilizing unit within a preset range, which is not affected by the output end load. Therefore, the stability of the LDO without external capacitors is also not affected by the output load, thereby improving the load transient response capability of the LDO without external capacitors. At the same time, the LDO without external capacitors can reduce the area of ​​the application board for the miniaturization and miniaturization of the chip.

[0054] In addition, the larger the capacitance of the compensation capacitor Cm is, the better the stability of the LDO without external capacitor. The selection of the compensation capacitor Cm is not specifically limited here and can be determined according to the actual situation, all within the protection scope of this application.

[0055] In addition, the LDO without an external capacitor may further include a load capacitor CL.

[0056] The load capacitor CL is disposed between the output end of the first switch tube MP and the ground GND. Specifically, one end of the load capacitor CL is connected to the output end of the first switch tube MP, and the other end of the load capacitor CL is grounded.

[0057] It should be noted that the load capacitor CL is a capacitor connected to the LDO output terminal inside the chip, which includes parasitic capacitance.

[0058] The load capacitor CL is arranged at the output end of the first switch tube MP, that is, at the output end of the LDO without an external capacitor, so that the output voltage of the LDO without an external capacitor can be stabilized within a preset range.

[0059] In practical applications, the voltage stabilizing unit may be a bandgap reference circuit, which may provide a stable output voltage. The specific structure thereof is not specifically limited here and may be determined according to the actual situation, and all are within the protection scope of this application.

[0060] The structure of the voltage stabilizing unit may include: an operational amplifier OP, a resistor feedback network (including Figure 2 Ract, R1 and R0 as shown) and the second switch tube MN1.

[0061] The output end of the operational amplifier OP is connected to the control end of the second switch tube MN1 and the control end of the first switch tube MP respectively; that is, the operational amplifier OP controls the second switch tube MN1 and the first switch tube MP respectively; further, the voltages of the ends of the two switch tubes that are not connected to the external power supply VDD are equal. That is, Figure 2 As shown, the voltage of the E node is equal to the voltage of the output terminal LDO_OUT.

[0062] The inverting input terminal of the operational amplifier OP is used to receive the reference voltage VREF; the non-inverting input terminal of the operational amplifier OP is used to receive the output voltage of the resistor feedback network.

[0063] The second switch tube MN1 and the resistor feedback network are connected in series between the external power supply VDD and the ground GND. That is, the input end of the second switch tube MN1 is connected to the external power supply VDD, the output end of the second switch tube MN1 is connected to one end of the resistor negative feedback network, and the other end of the resistor negative feedback network is grounded.

[0064] In practical applications, the resistor feedback network includes: a first resistor Ract, a second resistor R1 and a third resistor R0.

[0065] The first resistor Ract, the second resistor R1 and the third resistor R0 are connected in series in sequence; one end of the third resistor R0 is grounded GND; and the connection point between the second resistor R1 and the third resistor R0 serves as the output voltage of the resistor feedback network.

[0066] Specifically, one end of the first resistor Ract is connected to the output end of the second switch tube MN1; the other end of the first resistor Ract is connected to one end of the second resistor R1; the other end of the second resistor R1 is connected to one end of the third resistor R0, and the connection point serves as the output end of the resistor feedback network; the other end of the third resistor R0 is grounded GND.

[0067] In practical applications, the first resistor Ract is a variable resistor.

[0068] The first switch transistor MP and the second switch transistor MN1 are both NMOS transistors, or the first switch transistor MP and the second switch transistor MN1 are both PMOS transistors.

[0069] The function of the voltage stabilization unit is to determine the stable output voltage at point E, that is, the connection point between the second switch tube MN1 and the resistor feedback network. Since the first switch tube MP and the second switch tube MN1 are controlled by the same gate voltage, the output voltage of the LDO without external capacitor is also determined. The voltage at point E is determined by formula (1).

[0070] VE=VREF*(Ract+R0+R1) / R0 (Formula 1);

[0071] Wherein, VE is the voltage at point E, VREF is the reference voltage, Ract is the resistance value of the first resistor, R0 is the resistance value of the third resistor, and R1 is the resistance value of the second resistor.

[0072] Since the gate-source voltage VGS of the first switch tube MP and the second switch tube MN1 are substantially equal, that is, the gate and drain voltages of the first switch tube MP and the second switch tube MN1 are the same, when the current remains unchanged, it can be seen that the VGS of the two switches are approximately equal. Therefore, the output voltage of the LDO without external capacitors is also determined by this formula (1). That is, VLDO_OUT = VE; VLDO_OUT is the output voltage of the LDO without external capacitors. Even if the VGS of the two switches are not equal, the voltage difference between the two points is fixed, so the size of VLDO_OUT can be determined by the size of VE.

[0073] In this embodiment, a compensation unit Cm is provided between the output terminal of the operational amplifier OP and the ground; that is, the voltage difference between the output terminal of the operational amplifier OP and the ground does not change with the change of the load of the output terminal of the LDO without an off-chip capacitor, and the compensation unit Cm stabilizes the voltage of the output terminal of the operational amplifier OP within a preset range, and thus the gate terminal voltage of the first switch tube MP does not change with the load change, so that the output voltage of the first switch tube MP is stable, and the voltage stabilizing unit maintains good stability.

[0074] In practical applications, the LDO without external capacitors further includes: at least one current branch.

[0075] The current branch is used to adjust the current of the first switch tube MP when the load connected to the output terminal LDO_OUT of the LDO without an off-chip capacitor changes suddenly.

[0076] One end of the current branch is connected to the output end of the first switch tube MP, and the other end of the current branch is grounded. The first switch tube MP, the current branch and the load capacitor CL constitute the output stage of the LDO without an off-chip capacitor.

[0077] Specifically, the control end of the first switch tube MP is connected to the output end of the operational amplifier OP; the input end of the first switch tube MP is connected to the external power supply VDD, the output end of the first switch tube MP is respectively connected to one end of the load capacitor CL and one end of each current branch, and the other end of the load capacitor CL and the other end of each current branch are respectively connected to the ground GND. In other words, the current branch and the first switch tube MP are connected in series between the external power supply VDD and the ground GND.

[0078] Specifically, because the current branch connects the power supply to the ground through the first switch tube MP, the current branch can be regarded as the internal load of the LDO without an external capacitor; therefore, the current branch can have multiple forms, such as: the current branch includes: a controllable switch and a resistor connected in series; or the current branch includes: a controllable switch and a current source (such as Figure 2 IBN0, IBN1 or IBN2 shown); or, the current branch includes: a controllable switch and a current mirror connected in series; that is, the current branch is a part of the current mirror, so that the current in the current branch is copied by the current mirror.

[0079] The specific form of the current branch is not specifically limited here and may be determined according to actual conditions, and all are within the protection scope of this application.

[0080] When the load suddenly increases, causing the output voltage of the LDO without external capacitor to decrease, the current of the first switch MP is determined by formula (2):

[0081]

[0082] Wherein, Un is the electron mobility of the first switch tube MP, Cox is the gate oxide capacitance per unit area of ​​the first switch tube MP, W and L are the length and width of the first switch tube MP, VGS refers to the gate-source voltage of the first switch tube MP, VTH refers to the threshold voltage of the first switch tube MP; and I is the current of the first switch tube MP.

[0083] It can be seen from the above formula (2) that as the load current increases, VGS will also increase, which will cause the output voltage of the LDO without external capacitors to decrease; however, when the output voltage of the LDO without external capacitors decreases, due to the coupling effect of the parasitic capacitance between the gate terminal and the source terminal of the first switch tube MP, its gate terminal voltage decreases, so the output voltage of the LDO without external capacitors will be raised, thereby suppressing the decrease in the output voltage of the LDO without external capacitors; thereby improving the load transient response capability of the LDO.

[0084] Similarly, it can be seen from the above formula (2) that as the load current decreases, VGS will also decrease, which will cause the output voltage of the LDO without external capacitor to increase; however, when the output voltage of the LDO without external capacitor increases, due to the coupling effect of the parasitic capacitance between the gate terminal and the source terminal of the first switch tube MP, its gate terminal voltage will also increase, so it will suppress the increase of the output voltage of the LDO without external capacitor, thereby suppressing the output voltage overshoot of the LDO without external capacitor; thereby improving the load transient response capability of the LDO; that is, when the load current decreases, it can also well suppress the increase of the LDO output voltage.

[0085] It should be noted that the structure of the above-mentioned voltage stabilizing unit is only one implementation method of providing a driving voltage for the gate of the first switching tube MP. There are other methods to provide a stable reference voltage for the gate of the first switching tube MP. For example, a bandgap reference circuit can be used to provide a reference voltage for the gate of the first switching tube MP. They will not be described one by one here. The specific selection of the voltage stabilizing unit depends on the actual situation and is within the protection scope of this application.

[0086] When the total current IBNx of each current branch is large, the output voltage of the LDO without external capacitor decreases; at this time, in order to increase the output voltage of the LDO without external capacitor, the first resistor Ract will be opened, thereby increasing the output voltage of the LDO without external capacitor under large load current.

[0087] It should be noted that, from the above formula (1), when Ract increases, VE also increases, and VLDO_OUT=VE; therefore, increasing the resistance Ract can increase the output voltage.

[0088] When the first resistor Ract is not turned on, it is equivalent to that the first resistor Ract is short-circuited or is small enough to be regarded as short-circuited.

[0089] The first resistor Ract and the current branch are used in conjunction with each other. When all current branches are closed, the first resistor Ract is also closed, which is equivalent to being short-circuited. The larger the total current IBNx of each current branch, the more the first resistor Ract is opened, that is, the larger its resistance is, thereby increasing the output voltage of the LDO without external capacitors and stabilizing it within a reasonable indicator range.

[0090] like Figure 2 As shown, when the number of current branches is multiple, the internal load current can be increased in groups, that is, the internal load current of the LDO without external capacitor is increased according to the load capacity requirement.

[0091] Only one current branch can be invested, or multiple current branches can be invested. The specific number of current branches or the size of current branches depends on the load fluctuation. No specific limitation is made here. It can be determined based on the actual situation and is within the protection scope of this application.

[0092] It should be noted that when the number of current branches is one, the current branch is directly connected in series with the first switch tube MP; when the number of current branches is multiple, each current branch is connected in series with the first switch tube MP; that is, each current branch is connected in parallel, and each current branch is connected in series with the first switch tube MP.

[0093] The number of current branches can be set arbitrarily according to the requirements of load application. No specific limitation is made here. It can be determined according to the actual situation and is within the protection scope of this application.

[0094] It should be noted that the increase in the total current IBNx of each current branch can greatly enhance the load transient response capability; that is, the larger the internal load current, the better the load transient response characteristics. Therefore, the selection of each internal current is not specifically limited here, and it can be determined according to the actual situation, all within the protection scope of this application.

[0095] In this embodiment, in the structure without adding the current branch, it also has very good load transient response characteristics; of course, the addition of the current branch can better improve the load transient response characteristics of the LDO; when the current branch is added at the same time, its structure is simple and the circuit scale is small; at the same time, the load transient response capability is high; in addition, by opening and closing the current branch, that is, the circuit can be flexibly set, very low standby power consumption can be achieved.

[0096] In addition, due to the popularity of wearable devices, low-power design also poses a challenge, so low standby power consumption is also one of the requirements.

[0097] Therefore, when the LDO without external capacitors is in standby mode, each current branch needs to be closed, so that the LDO without external capacitors can basically be in standby mode with a power consumption of 1uA, thereby realizing the low power consumption design of the circuit.

[0098] The features recorded in the various embodiments in this specification can be replaced or combined with each other, and the same and similar parts between the various embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0099] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present invention.

[0100] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An LDO without external capacitor, characterized in that: include: A voltage stabilizing unit, a first switching tube and a compensation unit; The voltage stabilizing unit is used to stabilize the driving voltage received by the control end of the first switch tube within a preset range; The compensation unit is arranged at the output end of the voltage stabilizing unit; The input end of the first switch tube is used to be connected to an external power supply; The output end of the first switch tube serves as the output end of the LDO without an off-chip capacitor; The LDO without an external capacitor further includes a plurality of current branches connected to the output end of the first switch tube, wherein the current branches are used to adjust the current of the first switch tube when a load connected to the output end of the LDO without an external capacitor changes suddenly; Furthermore, each of the current branches includes a controllable switch; The voltage stabilizing unit comprises: an operational amplifier, a resistor feedback network and a second switch tube; The resistor feedback network includes an adjustable first resistor, and the greater the total current of each current branch, the greater the resistance of the first resistor.

2. The LDO without external capacitor according to claim 1, characterized in that: One end of the current branch is connected to the output end of the first switch tube; The other end of the current branch is grounded.

3. The LDO without external capacitor according to claim 1, characterized in that: The current branch includes: a current source connected in series with the controllable switch.

4. The LDO without external capacitor according to claim 1, characterized in that: The current branch includes: a current mirror connected in series with the controllable switch.

5. The LDO without external capacitor according to claim 1, characterized in that: The current branch includes: a resistor connected in series with the controllable switch.

6. The LDO without external capacitor according to any one of claims 1 to 5, characterized in that: The voltage stabilizing unit is a bandgap reference circuit.

7. The LDO without external capacitor according to any one of claims 1 to 5, characterized in that: The output end of the operational amplifier is connected to the control end of the second switch tube and the control end of the first switch tube respectively; The inverting input terminal of the operational amplifier is used to receive a reference voltage; The non-inverting input terminal of the operational amplifier is used to receive the output voltage of the resistor feedback network; The input end of the second switch tube is connected to the external power supply, and the output end of the second switch tube is connected to one end of the resistor feedback network; the other end of the resistor feedback network is grounded; The compensation unit is arranged between the output terminal of the operational amplifier and the ground.

8. The LDO without external capacitor according to claim 7, characterized in that: The first switch tube and the second switch tube are both PMOS tubes, or the first switch tube and the second switch tube are both NMOS tubes.

9. The LDO without external capacitor according to claim 7, characterized in that: The resistor feedback network further includes: a second resistor and a third resistor; One end of the first resistor serves as one end of the resistor feedback network; The other end of the first resistor is connected to one end of the second resistor; The other end of the second resistor is connected to one end of the third resistor, and the voltage at the connection point is used as the output voltage of the resistor feedback network; The other end of the third resistor is grounded.

10. The LDO without external capacitor according to any one of claims 1 to 5, characterized in that: The compensation unit is a compensation capacitor; The capacitance of the compensation capacitor is within a preset range.

11. The LDO without external capacitor according to any one of claims 1 to 5, characterized in that: Also includes: load capacitance; The load capacitor is arranged between the output end of the first switch tube and the ground.

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