Soft start circuit

Abstract

Embodiments of the present disclosure provide a soft start circuit. The circuit comprises a soft start module and a transconductance sampling module. Wherein the soft start module is configured to generate a first current signal and provide the first current signal to the transconductance sampling module via a first node; the transconductance sampling module is configured to generate a current shunt signal of the first current signal, and provide the current shunt signal to a charging capacitor in the soft start module via a second node. The embodiments of the present disclosure are suitable for the improvement of soft start circuit.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to the field of integrated circuit technology, and in particular, to a soft start circuit. BACKGROUND

[0002] In the working process of a switching power supply chip, in order to prevent a power tube in the chip from generating a large current peak at the initial stage of turning on, a soft start circuit is generally added in the chip to ensure that the current gradually increases to a target value smoothly and slowly.

[0003] However, the soft start circuit generally requires a large charging capacitor and a very small charging current. If a large capacitor is integrated on a chip, the chip area will be significantly increased, and the chip cost will be increased. SUMMARY

[0004] Embodiments of the present disclosure aim to provide a soft start circuit, which realizes a smaller charging capacitor in the soft start circuit by using a transconductance sampling amplification technology, thereby reducing the chip area and reducing the cost.

[0005] To achieve the above-mentioned purpose, a first aspect of embodiments of the present disclosure provides a soft start circuit, comprising: a soft start module and a transconductance sampling module. Wherein the soft start module is configured to generate a first current signal and provide the first current signal to the transconductance sampling module via a first node; the transconductance sampling module is configured to generate a current shunt signal of the first current signal, and provide the current shunt signal to a charging capacitor in the soft start module via a second node.

[0006] In some embodiments of the present disclosure, the soft start module comprises: a constant current source, a transistor, a voltage comparator, an inverter and a charging capacitor. Wherein a first end of the constant current source is coupled to a first voltage end, a second end of the constant current source is coupled to the first node; a control pole of the transistor is coupled to an output end of the inverter, a first pole of the transistor is coupled to the first voltage end, and a second pole of the transistor is coupled to the first node; a positive input end of the voltage comparator is coupled to the second node, a negative input end of the voltage comparator is coupled to a third voltage end, and an output end of the voltage comparator is coupled to an output end of the soft start circuit; an input end of the inverter is coupled to the output end of the voltage comparator; a first end of the charging capacitor is coupled to the second node, and a second end of the charging capacitor is coupled to a second voltage end.

[0007] In some embodiments of the present disclosure, the transconductance sampling module comprises a resistor and a transconductance amplifier. Wherein a first end of the resistor is coupled to the first node, and a second end of the resistor is coupled to the second node; a positive input end of the transconductance amplifier is coupled to the second node, a negative input end of the transconductance amplifier is coupled to the first node, and an output end of the transconductance amplifier is coupled to the negative input end of the transconductance amplifier.

[0008] In some embodiments of the present disclosure, the transistor is a PMOS transistor.

[0009] In some embodiments of the present disclosure, the first current signal is sampled by the resistor and the transconductance amplifier, and the first current signal is shunted by the transconductance amplifier to obtain the current shunt signal.

[0010] In some embodiments of the present disclosure, the power supply of the transconductance amplifier is coupled to the first voltage end and the second voltage end, respectively.

[0011] In some embodiments of the present disclosure, the current shunt signal is obtained by wherein R is the resistance of the resistor, gm is the transconductance of the transconductance amplifier, and I1 is the first current signal.

[0012] In some embodiments of the present disclosure, the capacitance of the charging capacitor is obtained by wherein C is the capacitance of the charging capacitor. ss wherein V3 is the input voltage of the third voltage end, and t is the start-up time of the soft start circuit.

[0013] In some embodiments of the present disclosure, the product of the transconductance of the transconductance amplifier and the resistance of the resistor is greater than or equal to 10.

[0014] A second aspect of the embodiments of the present disclosure provides a soft start circuit, comprising: a constant current source, a transistor, a voltage comparator, an inverter, a charging capacitor, a resistor and a transconductance amplifier. Wherein, a first end of the constant current source is coupled with a first voltage end, and a second end of the constant current source is coupled with the first node; a control pole of the transistor is coupled with an output end of the inverter, a first pole of the transistor is coupled with the first voltage end, and a second pole of the transistor is coupled with the first node; a positive input end of the voltage comparator is coupled with the second node, a negative input end of the voltage comparator is coupled with a third voltage end, and an output end of the voltage comparator is coupled with an output end of the soft start circuit; an input end of the inverter is coupled with the output end of the voltage comparator; a first end of the charging capacitor is coupled with the second node, and a second end of the charging capacitor is coupled with a second voltage end; a first end of the resistor is coupled with the first node, and a second end of the resistor is coupled with the second node; a positive input end of the transconductance amplifier is coupled with the second node, a negative input end of the transconductance amplifier is coupled with the first node, an output end of the transconductance amplifier is coupled with the negative input end of the transconductance amplifier, and power supply of the transconductance amplifier is coupled with the first voltage end and the second voltage end respectively.

[0015] By the above technical solution, the transconductance sampling amplification technology is adopted, so that a smaller charging capacitor in the soft start circuit is realized, the chip area is reduced, and the cost is reduced.

[0016] Other features and advantages of the embodiments of the present disclosure will be described in detail in the following specific implementation part. BRIEF DESCRIPTION OF DRAWINGS

[0017] The accompanying drawings are included to provide a further understanding of the embodiments of the present disclosure and constitute a part of the specification, and are used together with the following specific implementation to explain the embodiments of the present disclosure, but do not constitute a limitation on the embodiments of the present disclosure. In the drawings:

[0018] Figure 1 is an exemplary circuit diagram of a soft start circuit;

[0019] Figure 2 is a schematic block diagram of a soft start circuit according to the embodiments of the present disclosure;

[0020] Figure 3 is an exemplary circuit diagram of a soft start circuit according to the embodiments of the present disclosure. DETAILED DESCRIPTION

[0021] In order to make the purposes, technical solutions and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be described clearly and completely below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments of the present disclosure. Based on the described embodiments of the present disclosure, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the protection scope of the present disclosure.

[0022] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this present subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. As used herein, the statement that two or more parts are "connected" or "coupled" together will mean that the parts are joined together either directly or through one or more intermediate parts.

[0023] In all embodiments of the present disclosure, since the source and drain of the field effect tube are symmetrical, and the conduction current direction between the source and drain of the N-type field effect tube and the P-type field effect tube is opposite, in the embodiments of the present disclosure, the controlled middle end of the field effect tube is called the control electrode, and the remaining two ends of the field effect tube are called the first electrode and the second electrode, respectively. In addition, terms such as "first" and "second" are only used to distinguish one component (or part of a component) from another component (or another part of a component).

[0024] Figure 1 An exemplary circuit diagram of a soft start circuit 100 is shown. In Figure 1 In an example, a constant current source Iss generates a constant current I C to charge a charging capacitor Css, when the voltage SS_REF (i.e. the voltage of the positive input end of a voltage comparator COMP) of the charging capacitor Css rises to the reference voltage V BG of the negative input end of the voltage comparator COMP, the voltage comparator COMP flips the output to high level, so that SS_Done rises, the soft start ends, and the start time t ss of the soft start is achieved. The relationship between the constant current source Iss and the charging capacitor Css is shown in the following formula (1):

[0025]

[0026] It can be known from formula (1) that the capacitance value of the charging capacitor in the soft-start circuit is proportional to the charging current, the smaller the charging current is, the smaller the capacitance value of the charging capacitor is, and thus the smaller the area of the charging capacitor is. Therefore, the transconductance sampling amplification technology is adopted in the embodiments of the present disclosure, so that a smaller charging capacitor in the soft-start circuit is realized, the chip area is reduced, and the cost is lowered.

[0027] Figure 2 A schematic block diagram of a soft-start circuit 200 according to an embodiment of the present disclosure is shown. As shown, the soft-start circuit 200 can include a soft-start module 210 and a transconductance sampling module 220. Figure 2

[0028] The soft-start module 210 can be coupled to the transconductance sampling module 220, a first voltage terminal V1, a second voltage terminal V2, a third voltage terminal V3, and an output terminal OUT of the soft-start circuit. The soft-start module 210 is configured to generate a first current signal I1 and provide the first current signal I1 to the transconductance sampling module 220 via a first node N1.

[0029] The transconductance sampling module 220 can be coupled to the soft-start module 210, the first voltage terminal V1, and the second voltage terminal V2. The transconductance sampling module 220 is configured to generate a current shunt signal Is of the first current signal I1 and provide the current shunt signal Is to a charging capacitor in the soft-start module 210 via a second node N2.

[0030] The soft-start circuit according to the embodiments of the present disclosure effectively shunts the charging current through the transconductance sampling module, so that a smaller charging capacitor is realized, and the circuit area is saved.

[0031] Figure 3 An exemplary circuit diagram of a soft-start circuit 200 according to an embodiment of the present disclosure is shown. As shown, Figure 3 ​As shown, the soft start module 210 can include a constant current source Iss, a transistor M, a voltage comparator COMP, an inverter D and a charging capacitor Css. The first end of the constant current source Iss is coupled to a first voltage end V1, and the second end of the constant current source Iss is coupled to the first node N1. In the embodiments of the present disclosure, the specific circuit of the constant current source Iss is not limited as long as it can output a constant current. The control electrode of the transistor M is coupled to the output end of the inverter D, the first electrode of the transistor M is coupled to the first voltage end V1, and the second electrode of the transistor M is coupled to the first node N1. The transistor M is a PMOS transistor. The positive input end of the voltage comparator COMP is coupled to the second node N2, the negative input end of the voltage comparator COMP is coupled to a third voltage end V3, and the output end of the voltage comparator COMP is coupled to the output end OUT of the soft start circuit. The input end of the inverter D is coupled to the output end of the voltage comparator COMP. The first end of the charging capacitor Css is coupled to the second node N2, and the second end of the charging capacitor Css is coupled to a second voltage end V2.

[0032] The transconductance sampling module 220 can include a resistor R and a transconductance amplifier Gm. The first end of the resistor R is coupled to the first node N1, and the second end of the resistor R is coupled to the second node N2. The positive input end of the transconductance amplifier Gm is coupled to the second node N2, the negative input end of the transconductance amplifier Gm is coupled to the first node N1, and the output end of the transconductance amplifier Gm is coupled to the negative input end of the transconductance amplifier Gm. The power supply of the transconductance amplifier Gm is coupled to the first voltage end V1 and the second voltage end V2 respectively.

[0033] In the example shown in Figure 3 , the internal power supply Vdd of the switching power supply chip is input from the first voltage end V1, the second voltage end V2 is grounded, and a fixed power supply is input to the third voltage end, for example, the voltage of the fixed power supply is 1.2V. The output of the output end OUT can provide a signal for the subsequent circuit. Those skilled in the art should understand that the variants of the circuit shown in the above inventive concept should also fall within the protection scope of the present disclosure. In the variant, the transistors and voltage ends mentioned above can also have different settings from the example shown in Figure 3 . Figure 3

[0034] The working process of the over-temperature protection circuit 200 according to the embodiments of the present disclosure will be described below in conjunction with the example shown in Figure 3 .

[0035] ​The constant current source Iss can generate a constant first current signal I1 and provide the first current signal I1 to the transconductance sampling module 220. In this way, the first current signal I1 is sampled by the resistor R and the transconductance amplifier Gm, and then the first current signal I1 is precisely shunted by the transconductance amplifier Gm, so as to obtain a current shunt signal Is for charging the charging capacitor.

[0036] In Figure 3 In the example of the present disclosure, the current shunt signal Is can be obtained by the following formula (2):

[0037]

[0038] Wherein, R is the resistance of the resistor, and gm is the transconductance of the transconductance amplifier.

[0039] Thus, in the present disclosure Figure 3 In the example of the present disclosure, the charging capacitor C ss The capacitance of the charging capacitor C

[0040]

[0041] Wherein, V3 is the input voltage of the third voltage terminal, and t is the start-up time of the soft start circuit.

[0042] By comparing the capacitance formula (1) of the charging capacitor in the related art soft start circuit with the capacitance formula (3) of the charging capacitor in the soft start circuit of the present embodiment, it can be seen that, in the case of the same start-up time, first current signal, and input voltage of the third voltage terminal, the capacitance of the charging capacitor in the present embodiment is reduced by (1+gm·R) times compared with the original capacitance, greatly reducing the area of the charging capacitor, thereby saving the circuit area and cost. In the present embodiment, the product of the transconductance of the transconductance amplifier and the resistance of the resistor is greater than or equal to 10. For example, when gm·R is 19, if the original capacitance of the charging capacitor is 1 nF, the capacitance of the charging capacitor in the present embodiment is reduced by 20 times, to 50 pF.

[0043] After the constant current source generates a constant first current signal I1, the current sampling and shunting of the transconductance sampling module, and the charging of the charging capacitor Css by the current shunt signal Is, when the voltage SS_REF of the charging capacitor Css (i.e. the voltage of the positive input terminal of the voltage comparator COMP) rises to the fixed voltage of the third voltage terminal input to the negative input terminal of the voltage comparator COMP, the voltage comparator COMP flips to output a high level, so that OUT becomes high, the soft start ends, and then the low level after the flip of the inverter D controls the transistor M to be turned on, so that the voltage comparator COMP continues to output a high level to provide a high level signal for the subsequent circuit.

[0044] In summary, the charging capacitor in the soft start circuit according to the embodiments of the present disclosure has a small area and can save circuit area.

[0045] The flow diagrams and block diagrams in the drawings show the architectural, functional and operational views of possible implementations of apparatuses and methods according to various embodiments of the present disclosure. In this regard, each block in the flow diagrams and block diagrams can represent a module, a segment, or a portion of code that comprises one or more executable instructions for implementing the specified logical functions. In some alternative implementations, the functions noted in the blocks can occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently or in the reverse order, depending on the functionality involved. It will also be noted that each block of the block diagrams and / or flow diagrams, and combinations thereof, can be implemented by dedicated hardware-based systems that perform the specified functions or acts, or combinations of hardware and software.

[0046] Unless the context clearly indicates otherwise, as used herein and in the appended claims, the singular form "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Accordingly, the use of the articles "a," "an," and "the" as well as grammatical conjugations thereof are to be construed to be open ended, unless the context clearly indicates otherwise. Similarly, the words "comprise," "comprises," and "comprising" are to be construed as permissive, not as exclusive, unless the context clearly indicates otherwise. Likewise, the term "comprising" and "or" should be construed as inclusive or open-ended, unless the context clearly indicates otherwise. Where the term "example" is used in the following description, particularly in the context of a series of terms, the term "example" is merely indicative of one of the terms in the series and is not to be construed as an exclusive or exhaustive list of the terms in the series.

[0047] Further aspects and scope of adaptation will become apparent from the description provided herein. It should be understood that various aspects of the present application can be implemented alone or in combination with one or more other aspects. It should also be understood that the description and specific examples herein are intended to be illustrative only and are not intended to limit the scope of the present application.

[0048] The above detailed description of several embodiments of the present disclosure has been presented for the purposes of illustration and description. It is apparent to those skilled in the art that various modifications and variations can be made to the embodiments of the present disclosure without departing from the spirit and scope of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. A soft start circuit, characterized in that: include: Soft start module and transconductance sampling module, The soft start module is configured to generate a first current signal and provide the first current signal to the transconductance sampling module via a first node; The transconductance sampling module is configured to generate a current shunt signal of the first current signal, and provide the current shunt signal to the charging capacitor in the soft start module via the second node. The soft start module includes: a constant current source, a transistor, a voltage comparator, an inverter and a charging capacitor. Wherein, the first terminal of the constant current source is coupled to the first voltage terminal, and the second terminal of the constant current source is coupled to the first node; The control electrode of the transistor is coupled to the output terminal of the inverter, the first electrode of the transistor is coupled to the first voltage terminal, and the second electrode of the transistor is coupled to the first node; The positive input terminal of the voltage comparator is coupled to the second node, the negative input terminal of the voltage comparator is coupled to the third voltage terminal, and the output terminal of the voltage comparator is coupled to the output terminal of the soft start circuit; The input terminal of the inverter is coupled to the output terminal of the voltage comparator; The first terminal of the charging capacitor is coupled to the second node, and the second terminal of the charging capacitor is coupled to the second voltage terminal. Wherein, the transconductance sampling module includes: a resistor and a transconductance amplifier, Wherein, the first end of the resistor is coupled to the first node, and the second end of the resistor is coupled to the second node; A positive input terminal of the transconductance amplifier is coupled to the second node, an inverting input terminal of the transconductance amplifier is coupled to the first node, and an output terminal of the transconductance amplifier is coupled to the inverting input terminal of the transconductance amplifier.

2. The soft start circuit according to claim 1, wherein: The transistor is a PMOS transistor.

3. The soft start circuit according to claim 1, wherein: The first current signal is sampled through the resistor and the transconductance amplifier, and the first current signal is shunted through the transconductance amplifier to obtain the current shunting signal.

4. The soft start circuit according to claim 1, wherein: The power supply of the transconductance amplifier is coupled to the first voltage terminal and the second voltage terminal respectively.

5. The soft start circuit according to claim 1, wherein: The current shunt signal is obtained by: according to The current shunt signal Is is obtained, wherein R is the resistance of the resistor, gm is the transconductance of the transconductance amplifier, and I1 is the first current signal.

6. The soft start circuit according to claim 5, characterized in that: The capacitance of the charging capacitor is obtained by: according to Get the capacitance C of the charging capacitor ss , wherein V3 is the input voltage of the third voltage terminal, and t is the start-up time of the soft start circuit.

7. The soft start circuit according to claim 5, characterized in that: in, A product of a transconductance of the transconductance amplifier and a resistance value of the resistor is greater than or equal to 10.

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