Soft start circuit and low dropout regulator applied to same

Abstract

The invention relates to the technical field of soft start circuits, and provides a soft start circuit and a low dropout regulator applied to the soft start circuit. The circuit comprises: a ramp voltage generation module configured to charge a capacitor to generate a ramp voltage, the ramp voltage generation module comprising: a capacitor; the first charging branch is configured to charge the capacitor after the circuit is started; and a second charging branch configured to charge the capacitor after the circuit is started for a first period of time. Compared with the prior art, the starting time of the circuit is shorter, the surge current is smaller, and the circuit can be widely applied to various circuits which need to give consideration to performance indexes of the starting time and the surge current at the same time.

Description

Technical Field

[0001] The present invention generally relates to the technical field of soft start circuits. Specifically, the present invention relates to a soft start circuit and a low voltage drop linear regulator applied thereto. Background Art

[0002] Low dropout linear regulator (LD0) is a very important power management module, which is widely used in handheld devices and portable electronic products. In the design of LDO, it must be noted that when the power supply is powered on, the power tube of LDO will generate a large inrush current (Inrush), which is many times larger than the maximum load current output by LDO under stable conditions, which can easily damage its related components and even burn the LDO chip. In order to solve this problem, LDO needs to implement soft start when powered on to control the inrush current generated by the power tube, so as to ensure that the LDO chip and its internal related components are not damaged or burned.

[0003] However, in the prior art, when the external capacitor is large, in order to reduce the surge current, the startup time of the LDO is usually prolonged, which causes the LDO to have a problem of too long startup time. Summary of the invention

[0004] In order to at least partially solve the above problems in the prior art, the present invention provides a soft start circuit, comprising:

[0005] A ramp voltage generating module is configured to charge a capacitor to generate a ramp voltage, the ramp voltage generating module comprising:

[0006] capacitance;

[0007] A first charging branch, configured to charge the capacitor after the circuit is started; and

[0008] The second charging branch is configured to charge the capacitor after the circuit is started for a first period of time.

[0009] In one embodiment of the present invention, it is provided that the first power supply terminal is configured to make the surge current reach a maximum value within a first time period.

[0010] In one embodiment of the present invention, it is provided that the ramp voltage generating module includes: a first PMOS transistor, a second PMOS transistor, a third PMOS transistor, a current source, a capacitor, a first switch and a second switch.

[0011] In one embodiment of the present invention, it is provided that the ramp voltage generating module includes one or more second charging branches, wherein the plurality of second charging branches are connected in parallel with each other.

[0012] In one embodiment of the present invention, it is provided that the common point of the source of the first PMOS tube, the source of the second PMOS tube and the source of the third PMOS tube is the power supply terminal of the ramp voltage generating module.

[0013] In one embodiment of the present invention, it is provided that the input end of the current source is connected to the drain of the first PMOS tube, the gate of the first PMOS tube, the gate of the second PMOS tube and the gate of the third PMOS tube.

[0014] In one embodiment of the present invention, it is provided that the drain of the second PMOS tube is connected to the first end of the capacitor to form a first charging branch, wherein the first switch is connected in parallel with the capacitor.

[0015] In one embodiment of the present invention, the drain of the third PMOS tube is connected to the first end of the capacitor to form a second charging branch, wherein the second switch is arranged between the drain of the third PMOS tube and the first end of the capacitor.

[0016] In one embodiment of the present invention, it is provided that a common point between the output end of the current source and the second end of the capacitor is a ground end of the ramp voltage generating module.

[0017] In one embodiment of the present invention, it is provided that the soft start circuit further includes:

[0018] A voltage selection module is connected to the ramp voltage generation module, and is configured to select a smaller value between the ramp voltage and a fixed reference voltage as a reference voltage.

[0019] The present invention further provides a ramp voltage generating circuit, which is configured to charge a capacitor to generate a ramp voltage, wherein the ramp voltage generating circuit comprises:

[0020] capacitance;

[0021] A first charging branch, configured to charge the capacitor after the circuit is started; and

[0022] The second charging branch is configured to charge the capacitor after the circuit is started for a first period of time.

[0023] The present invention also provides a low voltage drop linear regulator having the soft start circuit.

[0024] The present invention has at least the following beneficial effects: the present invention proposes a soft start circuit, which has a shorter start-up time and a smaller surge current than the prior art, and can be widely used in various circuits that need to take into account the performance indicators of both start-up time and surge current (such as low-dropout linear regulators (LD0), DC-DC converters (DCDC), etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To further illustrate the advantages and features of various embodiments of the present invention, a more detailed description of various embodiments of the present invention will be presented with reference to the accompanying drawings. It will be understood that these drawings only depict typical embodiments of the present invention and are therefore not to be considered as limiting the scope thereof. In the accompanying drawings, for clarity, identical or corresponding parts will be represented by identical or similar reference numerals.

[0026] Figure 1 A circuit structure schematic diagram of a soft start circuit is shown.

[0027] Figure 2 A voltage waveform diagram of a soft start circuit is shown.

[0028] Figure 3 A circuit structure schematic diagram of a ramp voltage generating module of a soft start circuit according to an embodiment of the present invention is shown.

[0029] Figure 4 A circuit simulation waveform diagram of a soft start circuit in an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0030] It should be noted that the components in the figures may be shown exaggeratedly for the sake of illustration and are not necessarily true to scale. In the figures, identical or functionally identical components are provided with the same reference numerals.

[0031] In the present invention, unless otherwise specified, "arranged on...", "arranged above..." and "arranged above..." do not exclude the existence of an intermediate between the two. In addition, "arranged on or above..." merely indicates the relative positional relationship between two components, and in certain cases, such as after reversing the product direction, it can also be converted into "arranged below or below...", and vice versa.

[0032] In the present invention, each embodiment is only intended to illustrate the aspects of the present invention and should not be construed as limiting.

[0033] In the present invention, unless otherwise specified, the quantifiers "a", "an" and "an" do not exclude the presence of a plurality of elements.

[0034] It should also be noted that in the embodiments of the present invention, for the sake of clarity and simplicity, only a portion of the parts or components may be shown, but those of ordinary skill in the art will understand that under the teachings of the present invention, the required parts or components may be added according to the needs of the specific scenario. In addition, unless otherwise specified, the features in different embodiments of the present invention may be combined with each other. For example, a feature in the second embodiment may be used to replace a corresponding or functionally identical or similar feature in the first embodiment, and the resulting embodiment also falls within the disclosure scope or recorded scope of the present application.

[0035] It should also be noted that within the scope of the present invention, the terms "same", "equal", "equal to" and the like do not mean that the values ​​of the two are absolutely equal, but allow a certain reasonable error, that is, the terms also cover "substantially the same", "substantially equal", "substantially equal to". By analogy, in the present invention, the terms "perpendicular to", "parallel to" and the like indicating directions also cover the meanings of "substantially perpendicular to" and "substantially parallel to".

[0036] In the present application, the term "configuration" refers to the setting of the shape, structure, material and / or function of the target object to achieve the desired technical effect, wherein "configuration" includes a variety of alternative technical means for achieving the technical effect, which become obvious under the teaching of the present application.

[0037] In addition, the numbering of the steps of the methods of the present invention does not limit the execution order of the method steps. Unless otherwise specified, the method steps can be executed in different orders.

[0038] The present invention will be further described below in conjunction with specific embodiments with reference to the accompanying drawings.

[0039] Figure 1 A circuit structure schematic diagram of a soft start circuit is shown. Figure 2 A voltage waveform diagram of a soft start circuit is shown.

[0040] like Figure 1 and Figure 2 As shown, the soft start circuit includes a ramp voltage generating module 100 and a voltage selecting module 200. When the LDO is turned off, the ramp voltage (VRMP) is pulled down to ground through the N-type metal oxide semiconductor (NMOS) Mn5. When LD0 is started, the current generated by the P-type metal oxide semiconductor (PMOS) Mp10 charges the capacitor C1, so that VRMP gradually increases, and the output voltage of LD0 gradually increases with VRMP. When the error amplifier detects that VRMP is higher than the fixed reference voltage (VREF), the output voltage of the LDO is adjusted to follow VREF. Among them, the surge current I INRUSH , start-up time T, capacitor CTOTAL The relationship between the output voltage V can be expressed as follows:

[0041]

[0042] It can be seen from the above formula that when the external capacitance is large, in order to reduce the surge current, the startup time of LD0 needs to be extended. In view of the above problem, the present invention can accelerate the startup time of LD0 while ensuring that the surge current is within a reasonable range by controlling the VRMP rising slope in sections.

[0043] Figure 3 FIG. 2 shows a schematic diagram of a circuit structure of a ramp voltage generating module of a soft start circuit according to an embodiment of the present invention. Figure 3 As shown in FIG. 1 , after the LDO is started, the ramp voltage generating module first charges the capacitor C1 with the current I1. After the time t1 has passed, the second branch current I2 is added to charge the capacitor C1, so that the rising speed of VRMP is accelerated, thereby accelerating the startup time of the LDO. The value range of the t1 time is related to the process of the low voltage drop linear regulator, and it is necessary to ensure that the surge current reaches the maximum value within the t1 time. In addition, in addition to Figure 3 In addition to setting one second branch current as shown, a plurality of second branch currents may be set.

[0044] Specifically, the ramp voltage generating module includes a first PMOS transistor 301, a second PMOS transistor 302, a third PMOS transistor 303, a current source 304, a capacitor 305, a first switch 306, and a second switch 307. The common point of the source of the first PMOS transistor 301, the source of the second PMOS transistor 302, and the source of the third PMOS transistor 303 is the power supply terminal of the ramp voltage generating module. The input end of the current source 304 is connected to the drain of the first PMOS transistor 301, the gate of the first PMOS transistor 301, the gate of the second PMOS transistor 302, and the gate of the third PMOS transistor 303. The drain of the second PMOS transistor 302 is connected to the first end of the capacitor 305 to form a first charging branch, wherein the first switch 306 is connected in parallel with the capacitor 305. The drain of the third PMOS transistor 303 is connected to the first end of the capacitor 305 to form a second charging branch, wherein the second switch 307 is arranged between the drain of the third PMOS transistor 303 and the first end of the capacitor 306. The common point of the output end of the current source 304 and the second end of the capacitor 305 is the ground end of the ramp voltage generating module.

[0045] Figure 4 FIG. 2 shows a schematic diagram of circuit simulation waveforms of a soft start circuit according to an embodiment of the present invention. Figure 4As shown in the figure, the voltage of LDO has two rising slopes. In the first stage, the voltage rises at a relatively slow speed, and the LDO will have a large surge current in the first stage. In the second stage, the voltage rises at a faster speed, and the LDO current is basically stable during this period. Therefore, the VRMP rising speed can be accelerated to reduce the LDO startup time.

[0046] For example Figure 1 The soft start circuit shown and Figure 3 The soft start circuit shown in the figure is compared with the test (comparison conditions: TT, VCC: 2.0V, VCORE: 1.1V, 25℃, load capacitance: 3 2.2μF). According to the comparison results, it is found that Figure 1 In the soft start circuit shown in the figure, the start time is 150us and the surge current is 70mA. Figure 3 In the soft start circuit shown, the start time is 80us and the surge current is 60mA. It can be seen that the soft start circuit proposed by the present invention can greatly shorten the start time of the LDO while reducing the surge current.

[0047] Although various embodiments of the present invention are described above, it should be understood that they are presented as examples only and not as limitations. It is obvious to those skilled in the relevant art that various combinations, modifications and changes can be made thereto without departing from the spirit and scope of the present invention. Therefore, the breadth and scope of the present invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should only be defined according to the attached claims and their equivalents.

Claims

1. A soft start circuit, characterized in that: include: A ramp voltage generating module is configured to charge a capacitor to generate a ramp voltage, the ramp voltage generating module comprising: capacitance; A first charging branch, configured to charge the capacitor after the circuit is started; and The second charging branch is configured to charge the capacitor after the circuit is started for a first period of time.

2. The soft start circuit according to claim 1, characterized in that: The first power terminal is configured to make the surge current reach a maximum value within a first time period.

3. The soft start circuit according to claim 1, characterized in that: The slope voltage generating module includes one or more second charging branches, wherein the plurality of second charging branches are connected in parallel with each other.

4. The soft start circuit according to claim 1, characterized in that: The slope voltage generating module includes: a first PMOS transistor, a second PMOS transistor, a third PMOS transistor, a current source, a capacitor, a first switch and a second switch.

5. The soft start circuit according to claim 3, characterized in that: The common point of the source of the first PMOS tube, the source of the second PMOS tube and the source of the third PMOS tube is the power supply terminal of the ramp voltage generating module.

6. The soft start circuit according to claim 3, characterized in that: The input end of the current source is connected to the drain of the first PMOS tube, the gate of the first PMOS tube, the gate of the second PMOS tube and the gate of the third PMOS tube. A common point between the output end of the current source and the second end of the capacitor is a ground end of the ramp voltage generating module.

7. The soft start circuit according to claim 3, characterized in that: The drain of the second PMOS tube is connected to the first end of the capacitor to form a first charging branch, wherein the first switch is connected in parallel with the capacitor; and The drain of the third PMOS tube is connected to the first end of the capacitor to form a second charging branch, wherein the second switch is arranged between the drain of the third PMOS tube and the first end of the capacitor.

8. The soft start circuit according to claim 1, characterized in that: Also includes: A voltage selection module is connected to the ramp voltage generation module, and is configured to select a smaller value between the ramp voltage and a fixed reference voltage as a reference voltage.

9. A ramp voltage generating circuit, configured to charge a capacitor to generate a ramp voltage, wherein the ramp voltage generating circuit comprises: capacitance; A first charging branch, configured to charge the capacitor after the circuit is started; as well as The second charging branch is configured to charge the capacitor after the circuit is started for a first period of time.

10. A low voltage dropout linear regulator, characterized in that: A soft start circuit according to any one of claims 1 to 8.

Images