A load soft start circuit and method

Abstract

The present invention discloses a load soft start circuit and method. In the load soft start circuit, the first pole of a first transistor is connected to an input voltage, the second pole is connected to a load power supply voltage and a capacitive load branch, the third pole is connected to the first pole of a second transistor, the second pole of the second transistor is grounded, and the third pole is connected to the output end of a control branch. The input end of the control branch is connected to the input voltage and the first pole of the first transistor. The first end of an energy storage branch is connected to the input voltage and the first pole of the first transistor, and the second end is connected to the third pole of the first transistor and the first pole of the second transistor. When power is applied, the control branch is disconnected to make the second transistor cut off, so that the first transistor is cut off. After power is applied, the control branch is closed to make the second transistor conduct, and the slow discharge of energy from the energy storage branch to the ground is utilized to make the first transistor conduct slowly. The circuit design of the present invention is simple, with low cost and easy to implement, and is very suitable for the startup of pixel power supply and digital power supply of an image sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor integrated circuit design, and particularly to a load soft start circuit and a load soft start method applicable to an image sensor. Background Art

[0002] Currently, in a semiconductor integrated circuit test system or an application system, the load is no longer a pure resistive load, but mostly a capacitive load or an inductive load. In particular, in order to suppress transient current, a large-capacity capacitor is often added at the pin end of the load power supply (such as the Pixel power supply). Thus, due to the existence of the capacitive load, a large inrush current is often generated when the load is turned on, and in severe cases, it is easy to cause startup failure or burnout of the power chip.

[0003] Please refer to Figure 1 , which shows a traditional power-on circuit structure. As Figure 1 shown, the capacitor C2 representing the capacitive load L is connected to the load power supply voltage VDDP (the pin end of the load power supply). When power is applied, the switch S1 is closed. If the load transient current is large, such as the Pixel power supply (pixel power supply), digital power supply, etc. of an image sensor, then a large inrush current will be generated at the moment of turning on.

[0004] Please refer to Figure 2 , which shows an existing power-on circuit structure for limiting transient current. As Figure 2 shown, on the basis of the Figure 1 structure, a thermistor RT is provided between the switch S1 and the load power supply voltage VDDP. After power is applied, the resistance value of the thermistor RT is large, and it can divide the voltage with the load circuit where the capacitor C2 is located. As time goes by, the temperature of the thermistor RT rises, and the resistance value gradually becomes smaller, while at this time the load has been working stably. However, the disadvantage of this circuit structure is that the thermistor needs to be selected according to different capacitive loads.

[0005] According to the circuit principle, the electric quantity Q L at both ends of the capacitive load L L and the capacitance C L and the voltage U

[0006] at both ends of the capacitor satisfy the following formula (1): L Q L =C L ×U

[0007] At the same time, the electric quantity Q L at both ends of the load power supply bypass capacitor and the current I L flowing through both ends of the capacitor and the time t satisfy the following formula (2):

[0008] Q L= I L ×t (2)

[0009] So the current I flowing through both ends of the capacitor L satisfies the following formula (3):

[0010] I L = (C L ×U L ) / t (3)

[0011] Please refer to Figure 3 . When the load is turned on too quickly or urgently, and the load is suddenly powered on, a very large current is suddenly required. For example, when the pixel power supply voltage is 3.3V and the load is a large-capacity capacitor, the voltage rises to 3.3V instantaneously when it is turned on, that is, the waveform of the power supply voltage shows a relatively steep rise. At this time, the capacitor charging current will be very large. According to the above formula, if it only rises to 2.5V in the same time, the instantaneous current can be reduced.

[0012] Therefore, it is necessary to provide a new type of load turn-on circuit to solve the above problems existing in the prior art. Summary of the Invention

[0013] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a load soft turn-on circuit and method.

[0014] To achieve the above purpose, the technical solution of the present invention is as follows:[[]]

[0015] A load soft turn-on circuit includes:[[]]

[0016] A first transistor and a second transistor. The first pole of the first transistor is connected to the input voltage, the second pole is commonly connected to the load power supply voltage and the first end of a capacitive load branch, the third pole is connected to the first pole of the second transistor, the second pole of the second transistor is grounded, and the third pole is connected to the output end of a control branch. The input end of the control branch is commonly connected to the input voltage and the first pole of the first transistor, and the second end of the capacitive load branch is grounded;

[0017] An energy storage branch, whose first end is commonly connected to the input voltage and the first pole of the first transistor, and the second end is commonly connected to the third pole of the first transistor and the first pole of the second transistor;

[0018] When power is applied, the control branch is controlled to be disconnected, so that the second transistor is turned off, and the first transistor is turned off because the potential between its third pole and first pole is equal;

[0019] After power-on is completed, control the control branch to close, turn on the second transistor, and utilize the energy discharging process of the energy storage branch through the second transistor to the ground, so that the first transistor turns on as the potential difference between its third pole and first pole increases.

[0020] Further, the first transistor and the second transistor include MOS transistors.

[0021] Further, the first pole, second pole, and third pole of the MOS transistor are the source pole, drain pole, and gate pole respectively.

[0022] Further, the first transistor is a PMOS transistor, and the second transistor is an NMOS transistor.

[0023] Further, it further includes: a first voltage dividing branch to a fourth voltage dividing branch. The first end of the first voltage dividing branch is commonly connected to the second end of the energy storage branch and the third pole of the first transistor. The second end of the first voltage dividing branch is commonly connected to the second end of the second voltage dividing branch and the first pole of the second transistor. The first end of the second voltage dividing branch is commonly connected to the input voltage, the first end of the energy storage branch, and the first pole of the first transistor. The first end of the third voltage dividing branch is connected to the output end of the control branch and the third pole of the second transistor. The second end of the third voltage dividing branch is grounded. The first end of the fourth voltage dividing branch is commonly connected to the input voltage, the first end of the second voltage dividing branch, the first end of the energy storage branch, and the first pole of the first transistor. The second end of the fourth voltage dividing branch is connected to the input end of the control branch.

[0024] Further, a first resistor to a fourth resistor are correspondingly provided for the first voltage dividing branch to the fourth voltage dividing branch. The first ends of the first resistor to the fourth resistor are correspondingly used as the first ends of the first voltage dividing branch to the fourth voltage dividing branch, and the second ends of the first resistor to the fourth resistor are correspondingly used as the second ends of the first voltage dividing branch to the fourth voltage dividing branch.

[0025] Further, a switch is provided in the control branch. The input end of the switch is used as the input end of the control branch, and the output end of the switch is used as the output end of the control branch.

[0026] Further, a first capacitor is provided in the energy storage branch. The first end of the first capacitor is used as the first end of the energy storage branch, and the second end of the first capacitor is used as the second end of the energy storage branch.

[0027] Further, a second capacitor is provided in the capacitive load branch. The first end of the second capacitor serves as the first end of the capacitive load branch, and the second end of the second capacitor serves as the second end of the capacitive load branch.

[0028] A load soft start method using the above load soft start circuit includes the following steps:

[0029] When power is turned on, the control branch is disconnected, causing the second transistor to be cut off because its third pole is pulled low to a low level; the input voltage is used to charge the energy storage branch, causing the first transistor to be cut off because its third pole is pulled high to a high level and is at the same potential as its first pole;

[0030] After power-on is completed, the control branch is closed. The third pole of the second transistor is voltage-divided through the control branch, causing the second transistor to conduct because the voltage of its third pole is greater than the voltage of its first pole; by using the automatic energy discharge process of the energy storage branch from the first pole and the second pole of the second transistor to the ground, the voltage of the third pole of the first transistor drops, causing the first transistor to conduct as the potential difference between its third pole and its first pole increases.

[0031] Compared with the prior art, the present invention sets a first transistor as an opening switch in the load soft start circuit, connects the first transistor to an energy storage branch and a second transistor, and uses the energy discharge path formed when the second transistor conducts. During the process of the capacitor (the first capacitor) in the energy storage branch slowly discharging to the ground through the second transistor, through the discharge time of the capacitor, the first transistor is driven to slowly turn on (conduct) and finally fully turn on, thereby realizing the function of load soft start. The circuit design of the present invention is simple, with low cost and easy to implement, and is very suitable for the start of the Pixel power supply and digital power supply of image sensors. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of a traditional power supply start circuit.

[0033] Figure 2 It is a power supply start circuit structure for limiting transient current in the prior art.

[0034] Figure 3 For application Figure 1 The voltage waveform diagram when the load power supply of the circuit structure is powered on.

[0035] Figure 4 It is a schematic structural diagram of a load soft start circuit according to a preferred embodiment of the present invention.

[0036] Figure 5 For application Figure 4 The voltage waveform diagram when the load power supply of the circuit structure is powered on. Detailed Embodiments

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. The words such as "including" used herein mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0038] The following further elaborates on the specific implementation manners of the present invention in conjunction with the accompanying drawings.

[0039] Figure 4 It is a schematic structural diagram of a load soft start circuit according to a preferred embodiment of the present invention. As Figure 4 shown, a load soft start circuit of the present invention may include a connected first transistor M1 and a second transistor M2, an energy storage branch 12, a control branch 15, a voltage division branch, etc.

[0040] Please refer to Figure 4 . In the load soft start circuit, the first pole s1 of the first transistor M1 is connected to the input voltage. For example, for an input voltage of 3.3V, the second pole d1 of the first transistor M1 is commonly connected to the load power supply voltage VDDP and the first end of a capacitive load branch 11, and the third pole g1 of the first transistor M1 is connected to the first pole s2 of the second transistor M2.

[0041] The second pole d2 of the second transistor M2 is grounded, and the third pole g2 of the second transistor M2 is connected to the output end of the control branch 15.

[0042] The input end of the control branch 15 is commonly connected to the input voltage and the first pole s1 of the first transistor M1.

[0043] The second end of the capacitive load branch 11 is grounded.

[0044] The first end of the energy storage branch 12 is commonly connected to the input voltage and the first pole s1 of the first transistor M1, and the second end of the energy storage branch 12 is commonly connected to the third pole g1 of the first transistor M1 and the first pole s2 of the second transistor M2.

[0045] When power is turned on, by disconnecting the control branch 15, the second transistor M2 is turned off, causing the first transistor M1 to be turned off because the potential between its third pole g1 and first pole s1 is equal. After power-on is completed, by closing the control branch 15, the second transistor M2 is turned on, and by utilizing the energy-discharging process of the energy storage branch 12 through the second transistor M2 to the ground, the first transistor M1 is slowly turned on as the potential difference between its third pole g2 and first pole s2 gradually increases, thereby realizing the function of soft starting of the load.

[0046] In a preferred embodiment, the first transistor M1 and the second transistor M2 may include MOS transistors. Further, the first transistor M1 may be a PMOS transistor, the first pole s1 of the first transistor M1 may be the source of the PMOS transistor, the second pole d1 of the first transistor M1 may be the drain of the PMOS transistor, and the third pole g1 of the first transistor M1 may be the gate of the PMOS transistor.

[0047] The second transistor M2 may be an NMOS transistor, the first pole s2 of the second transistor M2 may be the source of the NMOS transistor, the second pole d2 of the second transistor M2 may be the drain of the NMOS transistor, and the third pole g2 of the second transistor M2 may be the gate of the NMOS transistor.

[0048] In a preferred embodiment, the load soft-starting circuit may further include a first voltage-dividing branch 13, a second voltage-dividing branch 14, a third voltage-dividing branch 16, and a fourth voltage-dividing branch 17. Among them, the first end of the first voltage-dividing branch 13 is commonly connected to the second end of the energy storage branch 12 and the third pole g1 of the first transistor M1, the second end of the first voltage-dividing branch 13 is commonly connected to the second end of the second voltage-dividing branch 14 and the first pole s2 of the second transistor M2, the first end of the second voltage-dividing branch 14 is commonly connected to the input voltage, the first end of the energy storage branch 12, and the first pole s1 of the first transistor M1, the first end of the third voltage-dividing branch 16 is connected to the output end of the control branch 15 and the third pole g2 of the second transistor M2, the second end of the third voltage-dividing branch 16 is grounded, the first end of the fourth voltage-dividing branch 17 is commonly connected to the input voltage, the first end of the second voltage-dividing branch 14, the first end of the energy storage branch 12, and the first pole s1 of the first transistor M1, and the second end of the fourth voltage-dividing branch 17 is connected to the input end of the control branch 15.

[0049] Further, the first voltage-dividing branch 13 may be provided with a first resistor R1, the second voltage-dividing branch 14 may be provided with a second resistor R2, the third voltage-dividing branch 16 may be provided with a third resistor R3, and the fourth voltage-dividing branch 17 may be provided with a fourth resistor R4. And, the control branch 15 may be provided with a switch S1, the energy storage branch 12 may be provided with a first capacitor c1, and the capacitive load branch 11 may be provided with a second capacitor c2.

[0050] Among them, the first end of the first resistor R1 serves as the first end of the first voltage dividing branch 13, and the second end of the first resistor R1 serves as the second end of the first voltage dividing branch 13; the first end of the second resistor R2 serves as the first end of the second voltage dividing branch 14, and the second end of the second resistor R2 serves as the second end of the second voltage dividing branch 14; the first end of the third resistor R3 serves as the first end of the third voltage dividing branch 16, and the second end of the third resistor R3 serves as the second end of the third voltage dividing branch 16; the first end of the fourth resistor R4 serves as the first end of the fourth voltage dividing branch 17, and the second end of the fourth resistor R4 serves as the second end of the fourth voltage dividing branch 17.

[0051] The input end of the switch S1 serves as the input end of the control branch 15, and the output end of the switch S1 serves as the output end of the control branch 15.

[0052] The first end of the first capacitor c1 serves as the first end of the energy storage branch 12, and the second end of the first capacitor c1 serves as the second end of the energy storage branch 12.

[0053] The first end of the second capacitor c2 serves as the first end of the capacitive load branch 11, and the second end of the second capacitor c2 serves as the second end of the capacitive load branch 11.

[0054] The load power supply voltage VDDP can be the voltage VDDP of the Pixel power supply pin of the image sensor or the voltage VDDP of the digital power supply pin.

[0055] In a preferred embodiment, the first end of the first resistor R1 is commonly connected to the second end of the first capacitor C1 and the gate of the first transistor M1, and is commonly connected to node A; the second end of the first resistor R1 is commonly connected to the second end of the second resistor R2 and the source of the second transistor M2, and is commonly connected to node B; the first end of the second resistor R2 is commonly connected to the input voltage, the first end of the fourth resistor R4, the first end of the first capacitor C1 and the source of the first transistor M1, and is commonly connected to node E on the line between the input voltage and the source of the first transistor M1; the first end of the third resistor R3 is commonly connected to the output end of the switch S1 and the gate of the second transistor M2, and is commonly connected to node C, and the second end of the third resistor R3 is grounded; the first end of the fourth resistor R4 is commonly connected to the input voltage, the first end of the second resistor R2, the first end of the first capacitor C1 and the source of the first transistor M1, and is commonly connected to node D on the line between the input voltage and the source of the first transistor M1, and the second end of the fourth resistor R4 is connected to the input end of the switch S1; the first end of the first capacitor C1 is commonly connected to the input voltage, the first end of the second resistor R2, the first end of the fourth resistor R4 and the source of the first transistor M1, and is commonly connected to node F on the line between the input voltage and the source of the first transistor M1; the drain of the first transistor M1 is commonly connected to the load power supply voltage VDDP and the first end of the second capacitor C2, and is commonly connected to node G on the line between the load power supply voltage VDDP and the first end of the second capacitor C2.

[0056] The following will combine with the drawings to elaborate in detail on a load soft start method of the present invention that adopts the above load soft start circuit.

[0057] Please refer to Figure 4 . When the load soft start circuit of the present invention is in use, in the initial state, the switch S1 is disconnected or a low level is input, so that the gate pin of the second transistor M2 is pulled low to a low level, then the second transistor M2 is turned off. At this time, the input voltage charges the first capacitor C1, and the gate pin of the first transistor M1 is at a high level, so the first transistor M1 is also turned off.

[0058] After that, the switch S1 is closed, and the gate pin of the second transistor M2 is divided by the third resistor R3 and the fourth resistor R4, so that the gate voltage V g of the second transistor M2 is greater than its source voltage V s , then the second transistor M2 is turned on.

[0059] After the second transistor M2 is turned on, the first capacitor C1 discharges slowly through the first resistor R1, the second transistor M2 to the ground (GND). At this time, the gate pin of the first transistor M1 slowly drops from the input voltage of 3.3V to 0V, and the voltage V gsIt increases slowly, causing the first transistor M1 to turn on slowly and finally fully turn on. At this time, the voltage Vgs of the first transistor M1 is about -3.3V. In this way, through the discharge time of the first capacitor c1, the slow turn-on of the first transistor M1 is achieved, thus realizing the function of soft start of the load.

[0060] The function of the second voltage division branch 14 is to ensure the normal charge and discharge function of the first capacitor c1 by using the provided second resistor R2.

[0061] Please refer to Figure 3 and Figure 5 , which is a comparison of the voltage waveforms when the load power is powered on between the circuit structures respectively applying Figure 1 and the load soft start circuit structure applying the present invention. Soft start means that the power supply is turned on slowly to limit the inrush current when the power supply starts. When the soft start function design is not added to the circuit, the rise of the power supply voltage will be relatively steep, as shown in Figure 3 . When the load soft start circuit of the present invention is adopted, due to the addition of the soft start function, the power supply switch will slowly turn on, and the power supply voltage will also slowly rise, and the rising edge will be relatively gentle, as shown in Figure 5 .

[0062] The load soft start circuit of the present invention can be provided on a semiconductor substrate and can be fabricated using CMOS technology, and is very suitable for the start of the Pixel power supply and digital power supply for image sensors.

[0063] Although the embodiments of the present invention have been described in detail above, it is obvious to those skilled in the art that various modifications and changes can be made to these embodiments. However, it should be understood that such modifications and changes are all within the scope and spirit of the present invention in the claims. Moreover, the present invention described herein can have other embodiments and can be implemented or realized in various ways.

Claims

1. A load soft start circuit, characterized in that, Comprising: A first transistor and a second transistor, a first pole of the first transistor is connected to an input voltage, a second pole is commonly connected to a load power supply voltage and a first end of a capacitive load branch, a third pole is connected to a first pole of the second transistor, a second pole of the second transistor is grounded, a third pole is connected to an output end of a control branch, an input end of the control branch is commonly connected to the input voltage and the first pole of the first transistor, and a second end of the capacitive load branch is grounded; An energy storage branch, a first end thereof is commonly connected to the input voltage and the first pole of the first transistor, and a second end is commonly connected to the third pole of the first transistor and the first pole of the second transistor; Wherein, when power is turned on, the control branch is controlled to be disconnected, so that the second transistor is cut off, and the first transistor is cut off because the potential between its third pole and first pole is equal; After power-on is completed, the control branch is controlled to be closed, so that the second transistor is turned on, and by using the energy dissipation process of the energy storage branch through the second transistor to the ground, the first transistor is turned on as the potential difference between its third pole and first pole increases; Further comprising: a first voltage dividing branch to a fourth voltage dividing branch, a first end of the first voltage dividing branch is commonly connected to the second end of the energy storage branch and the third pole of the first transistor, a second end of the first voltage dividing branch is commonly connected to a second end of the second voltage dividing branch and the first pole of the second transistor, a first end of the second voltage dividing branch is commonly connected to the input voltage, the first end of the energy storage branch and the first pole of the first transistor, a first end of the third voltage dividing branch is commonly connected to the output end of the control branch and the third pole of the second transistor, a second end of the third voltage dividing branch is grounded, a first end of the fourth voltage dividing branch is commonly connected to the input voltage, the first end of the second voltage dividing branch, the first end of the energy storage branch and the first pole of the first transistor, and a second end of the fourth voltage dividing branch is connected to the input end of the control branch; The first voltage dividing branch to the fourth voltage dividing branch are respectively provided with a first resistor to a fourth resistor, a first end of the first resistor to a first end of the fourth resistor respectively serve as the first end of the first voltage dividing branch to the first end of the fourth voltage dividing branch, and a second end of the first resistor to a second end of the fourth resistor respectively serve as the second end of the first voltage dividing branch to the second end of the fourth voltage dividing branch; The energy storage branch is provided with a first capacitor, a first end of the first capacitor serves as the first end of the energy storage branch, and a second end of the first capacitor serves as the second end of the energy storage branch.

2. The load soft start circuit according to claim 1, characterized in that, The first transistor and the second transistor comprise MOS transistors.

3. The load soft start circuit according to claim 2, wherein, A first pole, a second pole and a third pole of the MOS transistor are respectively a source electrode, a drain electrode and a gate electrode.

4. The load soft start circuit according to claim 3, wherein The first transistor is a PMOS transistor, and the second transistor is an NMOS transistor.

5. The load soft start circuit according to claim 1, characterized in that, The control branch is provided with a switch, an input end of the switch serves as the input end of the control branch, and an output end of the switch serves as the output end of the control branch.

6. The load soft start circuit according to claim 1, wherein The capacitive load branch is provided with a second capacitor. The first end of the second capacitor serves as the first end of the capacitive load branch, and the second end of the second capacitor serves as the second end of the capacitive load branch.

7. A load soft start method using the load soft start circuit according to any one of claims 1 to 6, characterized in that, It includes the following steps: When power is applied, the control branch is disconnected, causing the second transistor to be cut off because its third pole is pulled low to a low level; the energy storage branch is charged using the input voltage, causing the first transistor to be cut off because its third pole is pulled high to a high level and is at the same potential as its first pole. After power-on is completed, the control branch is closed, and the third pole of the second transistor is voltage-divided through the control branch, causing the second transistor to conduct because the voltage of its third pole is greater than the voltage of its first pole. Using the automatic energy dissipation process of the energy storage branch from the first pole and the second pole of the second transistor to the ground, the voltage of the third pole of the first transistor drops, causing the first transistor to conduct as the potential difference between its third pole and its first pole increases.

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