Digital auxiliary structure with adjustable LDO (Low Dropout Regulator) load current lower limit

Abstract

The invention discloses a digital auxiliary structure with an adjustable LDO (Low Dropout Regulator) load current lower limit, relates to the technical field of electronic equipment, and is used for solving the problems that a load is not normally started and works but the LDO still supplies power due to the fact that the minimum load current of normal work of the LDO cannot be limited in the prior art by improving the detection precision of the load current. And potential safety hazards or power consumption waste can be caused. Comprising an operational amplifier, an adjusting tube and a current detection tube, the width-to-length ratio of the current detection tube to the adjusting tube is 1: N; the load current on the adjusting tube is detected according to the one-Nth scaling; two input ends of the operational amplifier are respectively connected with the adjusting tube and the current detection tube, and grid electrodes and source electrodes of the adjusting tube and the current detection tube are connected. According to the structure provided by the invention, the minimum load current of the LDO is limited by detecting the load current very accurately, so that potential safety hazards caused when the load is not in a normal working current state and waste of power consumption of a power supply are prevented.

Description

Technical Field

[0001] The invention relates to the technical field of electronic equipment, and in particular to a digital auxiliary structure with an adjustable lower limit of an LDO load current. Background Art

[0002] LDO (Low Dropout Regulator) has extremely low self-noise and high power supply rejection ratio (PSRR). It is a new generation of integrated circuit regulator. Compared with the three-terminal regulator, LDO is a micro system on chip (SoC) with very low self-consumption. It is widely used in various electronic devices, especially in systems with high requirements for low noise, low power consumption and miniaturization design. For example, wireless communications, consumer electronics, automotive electronics, industrial control, medical equipment and other fields have widely used LDO as a power management component. With the continuous development of technology, the performance of LDO is also constantly improving. Lower voltage drop, higher output accuracy, wider input voltage range and smaller package size are the main development trends of LDO. These characteristics make LDO occupy an important position in modern power management systems and will continue to play an important role in future electronic devices.

[0003] However, traditional LDO designs have certain limitations in load current management, and the load current detection accuracy is low and cannot meet usage requirements.

[0004] Therefore, there is an urgent need to provide a more reliable digital auxiliary structure with adjustable lower limit of LDO load current. Summary of the invention

[0005] The purpose of the present invention is to provide a digital auxiliary structure with adjustable lower limit of LDO load current, which can improve the detection accuracy of load current to solve the problem that the minimum load current for normal operation of LDO cannot be limited in the prior art, resulting in the load not turning on and working normally but LDO still supplying power, which may cause safety hazards or power consumption waste. In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a digital auxiliary structure with an adjustable lower limit of an LDO load current, the digital auxiliary structure comprising at least:

[0007] Operational amplifier, adjustment tube, current detection tube;

[0008] The width-to-length ratio of the current detection tube to the adjustment tube is 1:N; the load current on the adjustment tube is detected at a scaling ratio of 1 / N;

[0009] The two input ends of the operational amplifier are connected to the adjustment tube and the current detection tube respectively, and the gates of the adjustment tube and the current detection tube are connected to the source.

[0010] Optionally, the digital auxiliary structure further includes:

[0011] A bandgap reference circuit module, an error amplifier, a comparator, a feedback tube, a switch tube, a first feedback resistor, a second feedback resistor and a detection resistor;

[0012] The source of the feedback tube and the first feedback resistor are both connected to the first input end of the error amplifier, the second input end of the error amplifier is connected to the bandgap reference circuit module, the output end of the error amplifier is connected to the gate of the current detection tube and the gate of the adjustment tube; the second feedback resistor is connected in parallel with the detection resistor.

[0013] Optionally, the source of the feedback tube and the detection resistor are both connected to the non-inverting input terminal of the comparator, the inverting input terminal of the comparator is connected to a fixed voltage, the output terminal of the comparator is connected to the gate of the switch tube, the drain of the switch tube is connected to the error amplifier, and the source of the switch tube is grounded;

[0014] The output end of the operational amplifier is connected to the gate of the feedback tube, the drain of the feedback tube is connected to the drain of the current detection tube, and the drain of the current detection tube is connected to the non-inverting input end of the operational amplifier, the source of the adjustment tube and the source of the current detection tube are both connected to a power supply, and the drain of the adjustment tube is connected to the inverting input end of the operational amplifier.

[0015] Optionally, the current detection tube and the feedback tube are on the same branch, the currents flowing through the current detection tube and the feedback tube are equal, the currents flowing through the current detection tube and the feedback tube are the detection currents that are obtained by reducing the load current by 1 / N, the detection currents will flow through the detection resistor to form a detection voltage; the detection voltage is input to the non-inverting input terminal of the comparator.

[0016] Optionally, the detection voltage is compared with the fixed voltage. If the detection voltage is greater than the fixed voltage, the inverter outputs a high level to turn on the switch tube, the error amplifier enters a normal working state, and the LDO circuit enters a normal working state.

[0017] Optionally, the error amplifier is a folded cascode operational amplifier, and the input stage of the error amplifier is a PMOS input.

[0018] Optionally, the operational amplifier is a Cascode operational amplifier including a Rail-to-Rail input structure, and the Rail-to-Rail input structure is used to increase the input voltage range of the operational amplifier; the error amplifier has the same bias circuit structure as the operational amplifier.

[0019] Optionally, the detection current adopts the formula: It is calculated that the resistance value of the detection resistor adopts the formula: Calculated;

[0020] Among them, I sense Represents the detection current, I load Represents the load current, R sense is the resistance value of the detection resistor, Vc represents a fixed voltage, and N is the ratio of the width to length ratio of the adjustment tube to the current detection tube.

[0021] Optionally, when the load current is less than a preset value, the detection current is too small, the detection voltage is also too small, the comparator outputs a low level, the switch tube is turned off, and the error amplifier cannot work normally.

[0022] Optionally, when the load current is greater than a preset value, the detection current is too large, the detection voltage is also too large, the detection voltage is greater than the fixed voltage, the comparator outputs a high level, the switch tube is turned on, and the error amplifier works normally.

[0023] Compared with the prior art, the present invention provides a digital auxiliary structure with adjustable lower limit of LDO load current. At least including: an operational amplifier, an adjustment tube, and a current detection tube; the width-to-length ratio of the current detection tube to the adjustment tube is 1:N; the load current on the adjustment tube is detected at a scaling ratio of one-N; the two input ends of the operational amplifier are respectively connected to the adjustment tube and the current detection tube, and the gate and source of the adjustment tube and the current detection tube are connected. In the digital auxiliary structure with adjustable lower limit of LDO load current provided by the present invention, the width-to-length ratio of the introduced current detection tube is 1:N with the original adjustment tube, and the load current on the adjustment tube can be detected at a scaling ratio of one-N; the "virtual short" function of the two input ends of the operational amplifier can make the drain voltage of the adjustment tube and the current detection tube basically consistent, and because the gate and source of the adjustment tube and the current detection tube are connected together, the load current can be detected very accurately. The digital auxiliary structure can limit the minimum load current for normal operation of the LDO, and the minimum load current value is achieved by adjusting the detection resistor value. By very accurately detecting the load current, the minimum load current of the LDO can be limited to prevent safety hazards and waste of power consumption when the load is not in a normal working current state. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0025] Figure 1 It is the basic module block diagram of LDO in the prior art;

[0026] Figure 2 A schematic diagram of a dynamic bias circuit in the prior art;

[0027] Figure 3 A schematic diagram of a digital auxiliary structure with adjustable lower limit of LDO load current provided by the present invention;

[0028] Figure 4 A schematic diagram of the structure of an error amplifier in a digital auxiliary structure with an adjustable lower limit of an LDO load current provided by the present invention;

[0029] Figure 5 A schematic diagram of the structure of an operational amplifier in a digital auxiliary structure with an adjustable lower limit of an LDO load current provided by the present invention;

[0030] Figure 6 This is a schematic diagram of the simulation results of the load current 6mA;

[0031] Figure 7 This is a schematic diagram of the simulation results of the load current 5mA;

[0032] Figure 8 This is a schematic diagram of the simulation results when the load current is slightly greater than 5mA.

[0033] Reference numerals:

[0034] 1-bandgap reference circuit module, 2-error amplifier, 3-first feedback resistor, 3'-second feedback resistor, 4-operational amplifier, 5-comparator, 6-detection resistor, PM1-current detection tube, PM2-adjustment tube, NM1-switch tube, NM2-feedback tube. DETAILED DESCRIPTION

[0035] In order to clearly describe the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, words such as "first" and "second" are used to distinguish the same items or similar items with basically the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and their order is not limited. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and execution order, and words such as "first" and "second" do not necessarily limit them to be different.

[0036] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0037] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0038] First, some abbreviations, English and key terms used in the embodiments of this specification are explained:

[0039] LDO: Low Dropout Regulator, low dropout linear regulator.

[0040] Vref: Voltage Reference, the reference voltage generated by the bandgap reference source.

[0041] EA: Error amplifier. Its main function is to increase the amplitude of certain frequencies of the input signal and decrease the amplitude of other frequencies.

[0042] Rail-to-Rail: Rail-to-rail, which means the voltage range can reach the power supply voltage at the highest and the ground level at the lowest.

[0043] Cascode: refers to the common source and common gate structure, which is a commonly used circuit structure in operational amplifier design.

[0044] In the prior art, Figure 1 FIG. 1 is a basic block diagram of LDO in the prior art. Figure 1 As shown in the figure, LDO is mainly composed of a bandgap reference source (providing Vref voltage), an error amplifier, a regulator tube and two feedback resistors. Its main function is to input a certain range of voltage and output a stable voltage, which is often used as a power supply to other modules.

[0045] The schematic diagram of the dynamic bias circuit in the prior art is as follows: Figure 2 As shown. Compared with the basic LDO circuit, a detection tube (PMS) is added to detect the load current in the main path. The source of the detection tube (PMS) is connected to the source of the adjustment tube (PM1), and the gate is also connected, so their gate-source voltages are approximately equal. In addition, the ratio of the width-to-length ratio (W / L) of PM1 to PMS is N:1. According to the saturation current formula of the MOS tube (1):

[0046]

[0047] It can be obtained that the current on the detection branch (I SENSE : Current in the load circuit (I LOAD )≈1:N. Then, the detection current (I SENSE ) is mirrored to Ibias. Due to the existence of the current mirror, Ibias and I SENSE Positive correlation. Ibias provides bias current to the error amplifier of the LDO, so that the bias current of the error amplifier will be positively correlated with the load current. When the load current increases, the bias current of the error amplifier will increase accordingly; when the load current decreases, the bias current of the error amplifier will decrease accordingly.

[0048] Although this structure in the prior art can improve the load transient response characteristics of the LDO circuit and adaptively adjust the power consumption, when the load current of the LDO is large, the bias current of the error amplifier will also increase, increasing the slew rate of the error amplifier output voltage, so that the LDO adjustment tube can quickly respond to the change of the load current. Due to the increase in the bias current of the error amplifier, the power consumption of the LDO will increase, but the ability to respond to load transients is improved. When the load current of the LDO is small, the bias current of the error amplifier will also be small. At this time, the load transient response ability of the LDO is weakened, but since a strong load transient response ability is not required when the load current is small, the impact is not significant. And due to the reduction of the bias current of the error amplifier, the power consumption of the LDO is reduced, realizing an adaptive power consumption adjustment function. However, in the scheme of the prior art, the current detection accuracy of the PMS tube and the PM1 tube is only close to 1:N, because the drain voltages of the PM1 tube and the PMS tube are not completely equal, and due to the channel length modulation effect of the device, the drain-source voltage will also affect the saturation region current, so the current detection accuracy is only approximately the ratio of the width-to-length ratio. That is, the existing technology cannot limit the minimum load current for the normal operation of the LDO, resulting in the load not turning on and working normally but the LDO still supplies power, which may cause safety hazards or waste of power consumption.

[0049] In order to overcome the defects in the prior art, the present invention improves the dynamic bias circuit structure of the LDO circuit, introduces the mirror current detection principle, realizes a digital auxiliary structure with adjustable lower limit of LDO load current, and proposes a digital auxiliary structure with adjustable lower limit of LDO load current. Next, the scheme provided by the embodiment of this specification is described in conjunction with the accompanying drawings:

[0050] like Figure 3 As shown, the present invention provides a digital auxiliary structure with adjustable lower limit of LDO load current, which may at least include:

[0051] Operational amplifier 4, adjustment tube PM2, current detection tube PM1;

[0052] The width-to-length ratio of the current detection tube PM1 to the adjustment tube PM2 is 1:N; the load current on the adjustment tube PM2 is detected at a scaling ratio of 1 / N;

[0053] The two input terminals of the operational amplifier 4 are respectively connected to the adjustment tube PM2 and the current detection tube PM1 , and the gates of the adjustment tube PM2 and the current detection tube PM1 are connected to the sources.

[0054] based on Figure 3 In the digital auxiliary structure with adjustable lower limit of LDO load current provided by the present invention, the width-to-length ratio of the introduced current detection tube PM1 is 1:N with the original adjustment tube PM2, and the load current on the adjustment tube PM2 can be detected at a scaling ratio of one-N; the "virtual short" function of the two input ends of the operational amplifier 4 can make the drain voltage of the adjustment tube PM2 and the current detection tube PM1 basically consistent, and because the gate and source of the adjustment tube PM2 and the current detection tube PM1 are connected together, the load current can be detected very accurately. The digital auxiliary structure can limit the minimum load current for normal operation of the LDO, and the minimum load current value is achieved by adjusting the detection resistor value. By very accurately detecting the load current, the minimum load current of the LDO is limited to prevent safety hazards when the load is not in a normal working current state and waste of power consumption.

[0055] based on Figure 3 The structure of this specification embodiment is also directed to Figure 3 The other structures in are described in detail.

[0056] like Figure 3 As shown, the digital auxiliary structure provided by the present invention may also include:

[0057] Bandgap reference circuit module 1, error amplifier 2, comparator 5, feedback tube NM2, switch tube NM1, first feedback resistor 3, second feedback resistor 3' and detection resistor 6;

[0058] The connection relationship of the above structure is:

[0059] The source of the feedback tube NM2 and the first feedback resistor 3 are connected to the first input end of the error amplifier 2, the second input end of the error amplifier 2 is connected to the bandgap reference circuit module 1, and the output end of the error amplifier 2 is connected to the gate of the current detection tube PM1 and the gate of the adjustment tube PM2; the second feedback resistor 3' is connected in parallel with the detection resistor 6.

[0060] The source of the feedback tube NM2 and the detection resistor 6 are both connected to the in-phase input terminal of the comparator 5, the inverting input terminal of the comparator 5 is connected to a fixed voltage, the output terminal of the comparator 5 is connected to the gate of the switch tube NM1, the drain of the switch tube NM1 is connected to the error amplifier 2, and the source of the switch tube NM1 is grounded;

[0061] The output end of the operational amplifier 4 is connected to the gate of the feedback tube NM2, the drain of the feedback tube NM2 is connected to the drain of the current detection tube PM1, and the drain of the current detection tube PM1 is connected to the non-inverting input end of the operational amplifier 4, the source of the adjustment tube PM2 and the source of the current detection tube PM1 are both connected to the power supply, and the drain of the adjustment tube PM2 is connected to the inverting input end of the operational amplifier 4.

[0062] The feedback voltage formed by the feedback resistor is connected to the non-inverting input terminal of the error amplifier 2 , and the reference voltage of the bandgap reference circuit module 1 is connected to the inverting terminal of the error amplifier 2 .

[0063] In the above structure, based on dynamic bias current technology and mirror current detection technology, different from the traditional LDO circuit, the structure in the present invention also includes a current detection tube PM1, a feedback tube NM2, a switch tube NM1, an operational amplifier 4, and a comparator 5. The current detection tube PM1 is a PMOS current detection tube, the feedback tube NM2 is an NMOS feedback tube, and the switch tube NM1 is an NMOS switch tube.

[0064] It should be noted that the operational amplifier 4 and the comparator 5 do not have lines connecting the power supply VDD and the ground GND, but there is a connection relationship in the actual circuit, which is not shown in the figure, and this does not affect the protection scope of the present invention.

[0065] Above Figure 3 The digital auxiliary structure in can achieve the following technical effects:

[0066] The width-to-length ratio of the current detection tube PM1 is 1:N with respect to the original adjustment tube PM2, so as to detect the load current on the adjustment tube PM2 at a scaling ratio of 1 / N.

[0067] The "virtual short" function of the two input terminals of the operational amplifier 4 can make the drain voltage of the adjustment tube PM2 and the current detection tube PM1 basically consistent, and because the gate and source of the adjustment tube PM2 and the current detection tube PM1 are connected together, the load current can be detected very accurately.

[0068] The feedback tube NM2 is added to form a closed-loop negative feedback, in which the non-inverting input terminal of the operational amplifier 4 is connected to the drain of the current detection tube PM1, and the reverse terminal is connected to the drain of the adjustment tube PM2. The operational amplifier 4 needs to be in a closed-loop negative feedback condition to realize the "virtual short" function.

[0069] Furthermore, as an optional implementation, the current detection tube PM1 and the feedback tube NM2 are on the same branch, the current flowing through the current detection tube PM1 and the feedback tube NM2 is equal, the current flowing through the current detection tube PM1 and the feedback tube NM2 is the detection current reduced by 1 / N of the load current, the detection current will flow through the detection resistor 6 to form a detection voltage; the detection voltage is input to the non-inverting input terminal of the comparator 5.

[0070] The detection voltage is compared with a preset fixed voltage (Vc). If the detection voltage is greater than the fixed voltage, the inverter will output a high level to turn on the switch tube NM1, and then the error amplifier 2 will enter a normal working state, and the LDO circuit will also enter a normal working state.

[0071] Next, for Figure 3 The structure of the error amplifier 2 and the operational amplifier 4 in the combination Figure 4 and Figure 5 For further explanation:

[0072] The structure of error amplifier 2 is as follows: Figure 4 As shown. The error amplifier 2 is a folded Cascode operational amplifier 4, in which the input stage is a PMOS input. The folded Cascode operational amplifier 4 consists of a differential input pair, a folded Cascode gain stage and an output stage. Among them, the folded Cascode gain stage is the core part, which adopts a transistor connection method similar to the conventional Cascode structure, but is folded to make the circuit structure more compact. Among them, the differential input pair can be composed of a pair of differential transistors for receiving input signals. The design of the differential input pair helps to reduce input noise and interference. The folded Cascode gain stage can be composed of multiple transistors, including at least one common source transistor and one common gate transistor. These transistors are connected by folding to form a folded Cascode structure. This structure can provide higher output impedance and gain, and at the same time help to expand the output swing. The output stage can be used to provide an amplified output signal.

[0073] Figure 4 In the embodiment, the error amplifier 2 of the present invention adopts a folded cascode structure to provide a higher single-stage gain, which helps to reduce the size and power consumption of the entire amplifier. The folded cascode has a larger output swing and can make more effective use of the power supply voltage. The purpose of adopting this structure in the present invention is to enable the amplifier to achieve a sufficiently high gain, mainly to satisfy its negative feedback function in the LDO circuit and stabilize the output voltage.

[0074] The structure of the operational amplifier 4 is a Rail-to-Rail input Cascode operational amplifier, such as Figure 5 As shown. Based on the error amplifier 2, a Rail-to-Rail input structure is added. The input voltage range of the operational amplifier 4 using the Rail-to-Rail input structure can be extended from the negative power supply voltage to the positive power supply voltage, almost covering the entire power supply voltage range. Among them, the Rail-to-Rail input structure usually uses back-to-back NPN and PNP input transistors, and a double-folded common emitter common base amplifier circuit. This design allows the input voltage to reach within a few millivolts of each power supply terminal, thereby achieving a rail-to-rail input characteristic.

[0075] In the present invention, the Rail-to-Rail input structure of the operational amplifier 4 can increase the input voltage range of the operational amplifier 4, which is conducive to adapting to the changes in the drain voltage of the current detection tube PM1 and the adjustment tube PM2 under different load current conditions.

[0076] Figure 4 and Figure 5 The error amplifier 2 and the operational amplifier 4 in the embodiment use the same bias circuit structure, which provides four bias voltages (VB1, VB2, VB3 and VB4) for the amplifier module. Since there are more transistor levels in the vertical direction from the power supply to the ground, the quiescent current of the bias circuit is relatively stable, so the bias voltage provided is also relatively stable.

[0077] In a specific implementation, the following technical solution may be used to calculate the detection current and the resistance value of the detection resistor 6:

[0078] If the operating current of the subsequent module powered by the LDO is known in advance, the detection current on the detection path when the module is working normally can be calculated by formula (2).

[0079]

[0080] Among them, I sense is the detection current, I loadis the load current, and N is the ratio of the width to length ratio of PM2 to PM1.

[0081] Since the fixed voltage (Vc) is fixed, the resistance value of the detection resistor 6 at this time can be calculated by equation (3).

[0082]

[0083] Among them, I sense is the detection current, R sense is the resistance value of the detection resistor 6, and N is the ratio of the width to length ratio of PM2 to PM1.

[0084] Knowing the load current in advance, we can preset the appropriate detection resistor value to achieve the function of adjusting the minimum value of the LDO load current. There are two working conditions:

[0085] Case 1: When the load current is less than the preset value, the detection current will be too small, so the detection voltage will also be too small. At this time, the comparator 5 will output a low level, turning off the switch tube NM1, the error amplifier 2 cannot work normally, and the adjustment tube PM2 of the LDO circuit will also be turned off, and will not supply power to the load.

[0086] Case 2: When the load current is greater than the preset value, the detection current will be too large, and the detection voltage will also be too large. Since the detection voltage is greater than the fixed voltage (Vc), the comparator 5 will output a high level, turning on the switch tube NM1, the error amplifier 2 will work normally, and the LDO circuit will normally supply power to the subsequent load.

[0087] In order to further illustrate the technical effect of a digital auxiliary structure with adjustable lower limit of LDO load current provided by the present invention, the following is an explanation in conjunction with a specific simulation diagram:

[0088] Simulation conditions: If the LDO circuit is to power a load with a normal operating current slightly greater than 5mA, the preset load current cannot be less than 5mA, the width-to-length ratio of PM2 to PM1 is 100, the fixed voltage Vc = 0.6V, and the detection resistance can be calculated to be approximately 12kΩ by the above formula (3).

[0089] Figure 6 In the example, the load is connected to a 500Ω resistor. Since the output voltage of the LDO is 3V, the load current should be 6mA, and the LDO should be able to supply power normally. That is, the load current needs to be adjusted to 6mA by adjusting the load resistor, and then the LDO can supply power normally.

[0090] Figure 7In the example, the load is connected to a 600Ω resistor. Since the output voltage of the LDO is 3V, the load current should be 5mA. In the actual circuit simulation, the detection current will be slightly less than 50μA. Therefore, the LDO circuit cannot work normally at this time. That is, when the load current is adjusted to 5mA by adjusting the load resistance, the LDO cannot supply power.

[0091] Figure 8 In the example, the load is connected to a 580Ω resistor. Since the output voltage of the LDO is 3V, the load current will be slightly greater than 5mA. At this time, the LDO circuit should be able to work normally, that is, by adjusting the load resistance, the load current is adjusted to slightly greater than 5mA (about 5.2mA). At this time, the LDO can supply power normally.

[0092] Therefore, through the digital auxiliary structure with adjustable lower limit of LDO load current provided by the present invention and the simulation results, it can be determined that the digital auxiliary structure provided by the present invention can limit the minimum load current for normal operation of LDO, and the minimum load current value is achieved by adjusting the detection resistor value. By very accurately detecting the load current, the minimum load current of LDO is limited to prevent safety hazards and waste of power consumption when the load is not in a normal working current state.

[0093] The present invention introduces the mirror current detection principle into the switch control of the LDO, forming a digital auxiliary structure to limit the minimum value of the load current that the LDO can provide. The current detection negative feedback loop and the comparator 5 are used together. The lower limit value of the load current that the LDO circuit can carry is regulated, so that it can work normally only under the condition that the load current it carries is greater than the preset lower limit value. For example, if this technology is used to regulate an LDO circuit, by setting it so that the load current it carries for normal operation must not be less than 5mA, then the LDO can only power a load with an operating current greater than 5mA. This digital auxiliary structure can prevent safety hazards when the load is not in a normal operating current state and waste of power supply power.

[0094] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0095] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A digital auxiliary structure with adjustable lower limit of LDO load current, characterized in that: The digital auxiliary structure includes at least: Operational amplifier, adjustment tube, current detection tube; The width-to-length ratio of the current detection tube to the adjustment tube is 1:N; the load current on the adjustment tube is detected at a scaling ratio of 1 / N; The two input ends of the operational amplifier are connected to the adjustment tube and the current detection tube respectively, and the gates of the adjustment tube and the current detection tube are connected to the source.

2. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 1, characterized in that: The digital auxiliary structure also includes: A bandgap reference circuit module, an error amplifier, a comparator, a feedback tube, a switch tube, a first feedback resistor, a second feedback resistor and a detection resistor; The source of the feedback tube and the first feedback resistor are both connected to the first input end of the error amplifier, the second input end of the error amplifier is connected to the bandgap reference circuit module, the output end of the error amplifier is connected to the gate of the current detection tube and the gate of the adjustment tube; the second feedback resistor is connected in parallel with the detection resistor.

3. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 2, characterized in that: The source of the feedback tube and the detection resistor are both connected to the non-inverting input terminal of the comparator, the inverting input terminal of the comparator is connected to a fixed voltage, the output terminal of the comparator is connected to the gate of the switch tube, the drain of the switch tube is connected to the error amplifier, and the source of the switch tube is grounded; The output end of the operational amplifier is connected to the gate of the feedback tube, the drain of the feedback tube is connected to the drain of the current detection tube, and the drain of the current detection tube is connected to the non-inverting input end of the operational amplifier, the source of the adjustment tube and the source of the current detection tube are both connected to a power supply, and the drain of the adjustment tube is connected to the inverting input end of the operational amplifier.

4. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 2, characterized in that: The current detection tube and the feedback tube are on the same branch, the currents flowing through the current detection tube and the feedback tube are equal, the currents flowing through the current detection tube and the feedback tube are the detection currents that are reduced by 1 / N from the load current, the detection currents will flow through the detection resistor to form a detection voltage; the detection voltage is input to the non-inverting input terminal of the comparator.

5. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 3, characterized in that: The detection voltage is compared with the fixed voltage. If the detection voltage is greater than the fixed voltage, the inverter outputs a high level to turn on the switch tube, the error amplifier enters a normal working state, and the LDO circuit enters a normal working state.

6. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 2, characterized in that: The error amplifier is a folded cascode operational amplifier, and the input stage of the error amplifier is a PMOS input.

7. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 6, characterized in that: The operational amplifier is a Cascode operational amplifier including a Rail-to-Rail input structure, and the Rail-to-Rail input structure is used to increase the input voltage range of the operational amplifier; the error amplifier and the operational amplifier have the same bias circuit structure.

8. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 4, characterized in that: The detection current adopts the formula: It is calculated that the resistance value of the detection resistor adopts the formula: Calculated; Among them, I sense Represents the detection current, I load Represents the load current, R sense is the resistance value of the detection resistor, Vc represents a fixed voltage, and N is the ratio of the width to length ratio of the adjustment tube to the current detection tube.

9. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 4, characterized in that: When the load current is less than a preset value, the detection current is too small, the detection voltage is also too small, the comparator outputs a low level, the switch tube is turned off, and the error amplifier cannot work normally.

10. The digital auxiliary structure with adjustable lower limit of LDO load current according to claim 8, characterized in that: When the load current is greater than a preset value, the detection current is too large, the detection voltage is also too large, the detection voltage is greater than the fixed voltage, the comparator outputs a high level, the switch tube is turned on, and the error amplifier works normally.

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