High-precision sampling circuit for source electrode driving

Abstract

The invention relates to the technical field of power supplies, and particularly discloses a high-precision sampling circuit for source electrode driving, which comprises a power tube (P1), a sampling tube (S1), a driving unit (D1), an operational amplifier (A1), an adjusting tube (T1), a mirror image module (M1), a resistor (R1) and a comparator (C1), the sampling tube (S1) is used for carrying out current fixed proportion sampling on the power tube (P1); the driving unit (D1) is used for controlling the on-off of the sampling tube (S1), the power tube (P1) and the operational amplifier (A1); the adjusting tube (T1) adjusts the drain electrode potential of the sampling tube (S1) in real time according to the input and output state of the operational amplifier (A1) so as to ensure that the drain electrode potential of the sampling tube (S1) and the drain electrode potential of the power tube (P1) are equal in the sampling stage, and therefore sampling current (ISAM) related to the area ratio is obtained; the mirror image module (M1) is used for reetching the sampling current (ISAM) and enabling the sampling current (ISAM) to flow through the resistor (R1) to form sampling voltage; when the sampling voltage exceeds the reference voltage (VREF), the comparator (C1) outputs a signal to control the driving unit (D1) to be turned off.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a high-precision sampling circuit for source driving. Background Art

[0002] In switching power supplies, source drive is widely used due to its low power consumption and high efficiency. For applications, on the one hand, the application of source drive can omit the traditional external CS resistor solution and reduce the cost of the entire system; on the other hand, because the lower drive tube set by the source drive works in the linear region, its on-resistance is very small, and the heat loss generated during the entire working stage can be ignored. The application of source drive can greatly improve the overall efficiency of the switching power supply. Therefore, for applications with high efficiency requirements, the source drive module is indispensable.

[0003] The application solution using source drive inevitably requires current sampling of the source drive power tube to obtain accurate inductor current information, and at the same time sends the sampling results to the internal module for processing, thereby achieving the stability of the switching power supply system.

[0004] The traditional source drive sampling method is relatively simple, such as Figure 1 As shown, by connecting a resistor to the source of the power tube, when the voltage on the resistor reaches a preset value, the power tube is turned off. However, in actual work, when the resistor is connected to the source of the power tube, on the one hand, due to the large power current, the resistor must be very small, and in the design of integrated circuits, resistors with small resistance and excessive current often occupy a large amount of chip area; on the other hand, the resistor and the power tube form a source negative feedback, that is, the power current will superimpose the voltage on the resistor, thereby seriously weakening the driving effect of the drive unit on the power tube. If the driving effect is not good, the area of ​​the power tube must be further increased, and the chip cost will increase sharply. Therefore, the sampling accuracy in the traditional sampling method is acceptable, but the cost is too high.

[0005] Therefore, a new high-precision sampling circuit for source driving is needed, which can effectively reduce the design cost while improving the sampling accuracy of the source driving solution. Summary of the invention

[0006] In view of the above problems, an object of the present invention is to provide a high-precision sampling circuit for source driving, so as to solve the problem of not reducing the sampling accuracy but also reducing the cost.

[0007] The present invention provides a high-precision sampling circuit for source driving, comprising: a power tube, a sampling tube, a driving unit, an operational amplifier, an adjustment tube, a mirror module, a resistor and a comparator;

[0008] The sampling tube is used to perform current fixed-ratio sampling on the power tube;

[0009] The driving unit is used to control the on and off of the sampling tube, the power tube and the operational amplifier;

[0010] The adjustment tube adjusts the drain potential of the sampling tube in real time according to the input and output states of the operational amplifier to ensure that the drain potentials of the sampling tube and the power tube are equal during the sampling phase, thereby obtaining a sampling current related to the area ratio;

[0011] The mirror module is used to replicate the sampling current and make the sampling current flow through the resistor to form a sampling voltage;

[0012] When the sampled voltage exceeds the reference voltage, the comparator outputs a signal to control the driving unit to be turned off.

[0013] In a possible implementation, the drain of the power tube is connected to the power switch 103; the drain of the sampling tube is connected to the source of the adjustment tube; the gates of the power tube and the sampling tube are respectively connected to the driving unit;

[0014] The driving unit is also connected to the enable EN of the operational amplifier, the positive input terminal of the operational amplifier is connected to the drain of the power tube, the negative input terminal of the operational amplifier is connected to the drain of the sampling tube, and the output terminal of the operational amplifier is connected to the gate of the adjustment tube;

[0015] One end of the mirror module is connected to the drain of the adjustment tube, and the other end is respectively connected to the resistor and the positive input end of the comparator, the negative input end of the comparator is connected to the reference voltage, and the output end of the comparator is connected to the driving unit.

[0016] In a possible implementation, in the sampling phase, the driving unit controls the sampling tube and the power tube to be turned on and off at the same time, and provides the same driving voltage to the sampling tube and the power tube.

[0017] In a possible implementation, in the sampling phase, the driving unit controls the on-off of the operational amplifier so that the operational amplifier, the adjustment tube and the sampling current form a strong negative feedback modulation path;

[0018] The two input terminals of the operational amplifier are forced to be equal under the action of the negative feedback modulation path, so that the drain voltage of the sampling tube follows the change of the drain voltage of the power tube in real time and remains consistent.

[0019] In a possible implementation, the drain voltage of the power tube is the product of the power current and the corresponding first on-resistance; the drain voltage of the sampling tube is the product of the sampling current and the corresponding second on-resistance.

[0020] In a possible implementation manner, the sampling ratio of the sampling current to the power current is the area ratio of the sampling tube to the power tube.

[0021] In a possible implementation, the sampling tube and the power tube are devices of the same type and have consistent device characteristic parameters.

[0022] In a possible implementation, the sampling tube, the power tube and the adjustment tube are all N-type MOS tubes.

[0023] In a possible implementation manner, the resistor is a zero temperature coefficient resistor.

[0024] In a possible implementation manner, the reference voltage is a zero temperature coefficient voltage.

[0025] The high-precision sampling circuit for source driving provided by the present invention can improve the sampling accuracy of the sampling tube for the power tube and avoid the problem of system instability caused by sampling mismatch, because the ratio of the current flowing through the sampling tube and the power tube is only related to the area ratio of the two and has nothing to do with other factors; since the area of ​​the sampling tube is very small, the design of the operational amplifier, comparator, etc. is also extremely simple, which can greatly reduce the design cost of the chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A sampling circuit diagram for source driving in the prior art;

[0027] Figure 2 is a circuit diagram of a high-precision sampling circuit in an embodiment of the present invention;

[0028] Figure 3 is a data state diagram of the sampling current in an embodiment of the present invention;

[0029] in, Figure 2 The symbols are: 101 - high-precision sampling circuit; 101 - voltage source; 102 - power inductor; 103 - power switch. DETAILED DESCRIPTION

[0030] The following detailed description of the embodiments of the present invention is further described in detail in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to exemplarily illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the preferred embodiments described, and the scope of the present invention is defined by the claims.

[0031] In the description of the present invention, it should be noted that, unless otherwise specified, “plurality” means two or more than two; the terms “first”, “second”, etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance; for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0032] Figure 2 is a circuit diagram of a high-precision sampling circuit in an embodiment of the present invention, such as Figure 2 As shown, the present invention provides a high-precision sampling circuit for source driving, which can be applied to a switching power supply system, can effectively improve the stability of the switching power supply system, and avoid system instability caused by sampling mismatch. The high-precision sampling circuit for source driving of the present invention includes: a power tube P1, a sampling tube S1, a driving unit D1, an operational amplifier A1, an adjustment tube T1, a mirror module M1, a resistor R1 and a comparator C1;

[0033] The drain of the power tube P1 is connected to the power switch 103; the drain of the sampling tube S1 is connected to the source of the adjustment tube T1; the gates of the power tube P1 and the sampling tube S1 are connected to the driving unit D1 respectively;

[0034] The driving unit D1 is also connected to the enable EN of the operational amplifier A1, the positive input terminal of the operational amplifier A1 is connected to the drain of the power tube P1, the negative input terminal of the operational amplifier A1 is connected to the drain of the sampling tube S1, and the output terminal of the operational amplifier A1 is connected to the gate of the adjustment tube T1;

[0035] One end of the mirror module M1 is connected to the drain of the adjustment tube T1, and the other end is respectively connected to the resistor R1 and the positive input end of the comparator C1. The negative input end of the comparator C1 is connected to the reference voltage VREF, and the output end of the comparator C1 is connected to the driving unit D1.

[0036] Among them, the sampling tube S1 is used to perform current fixed ratio sampling on the power tube P1;

[0037] The driving unit D1 is used to control the on and off of the sampling tube S1, the power tube P1 and the operational amplifier A1;

[0038] The adjustment tube T1 adjusts the drain potential of the sampling tube S1 in real time according to the input and output state of the operational amplifier A1, so as to ensure that the drain potentials of the sampling tube S1 and the power tube P1 are equal during the sampling phase, thereby obtaining the sampling current ISAM related to the area ratio;

[0039] The mirror module M1 is used to replicate the sampling current ISAM and make the sampling current ISAM flow through the resistor R1 to form a sampling voltage;

[0040] When the sampled voltage exceeds the reference voltage VREF, the comparator C1 outputs a signal to control the driving unit D1 to turn off.

[0041] In a possible implementation, during the sampling phase, the driving unit D1 controls the sampling tube S1 and the power tube P1 to be turned on and off at the same time, and gives the sampling tube S1 and the power tube P1 the same driving voltage, that is, VGS-S1=VGS-P1=V1, and the V1 voltage needs to be large enough to enable the sampling tube S1 and the power tube P1 to operate in the linear resistance region; when turned off, VGS-S1=VGS-P1=0v.

[0042] In a possible implementation, during the sampling phase, the driving unit D1 controls the on-off of the operational amplifier A1, so that the operational amplifier A1, the adjustment tube T1 and the sampling current ISAM form a strong negative feedback modulation path;

[0043] The two input terminals of the operational amplifier A1 will be forced to be equal under the action of the negative feedback modulation path, so that the drain voltage of the sampling tube S1 follows the change of the drain voltage of the power tube P1 in real time and remains consistent, that is, VDS-S1=VDS-P1.

[0044] In a possible implementation, the drain voltage of the power tube P1 is the product of the power current and the corresponding first on-resistance; the drain voltage of the sampling tube S1 is the product of the sampling current and the corresponding second on-resistance.

[0045] In a possible implementation, the sampling ratio of the sampling current ISAM to the power current is the area ratio of the sampling tube S1 to the power tube P1.

[0046] In a possible implementation, the sampling tube S1 and the power tube P1 are the same type of devices and have the same device characteristic parameters. The current sampling ratio of the sampling tube S1 to the power tube P1 is the area ratio; in the conduction phase, the sampling tube S1 and the power tube P1 both work in the linear resistance region to reduce power consumption. The on-resistance ratio of the sampling tube S1 to the power tube P1 is the inverse ratio of the area. Assuming that the sampling ratio of the sampling tube S1 to the power tube P1 is 1:N, then the on-resistance ratio of the sampling tube S1 to the power tube P1 RDS-S1 / RDS-P1=N.

[0047] The drain of the sampling tube S1 and the drain of the power tube are kept consistent under the action of strong negative feedback; the power current flowing into the power tube P1 in the conduction stage increases linearly, and the drain voltage of the power tube P1 is the product of the power current and its on-resistance, that is: VDS-P1=IL* / RDS-P1, and the drain voltage of the sampling tube S1 is the product of the sampling current and its on-resistance, that is: VDS-S1=ISAM*RDS-S1.

[0048] As is known from the above, the on-resistance ratio of the sampling tube S1 to the power tube P1 is N, and VDS-S1=VDS-P1, then the sampling ratio of the sampling current to the power current is the area ratio of the sampling tube S1 to the power tube P1 1 / N.

[0049] In a possible implementation, the sampling tube S1, the power tube P1 and the adjustment tube T1 are all N-type MOS tubes. The area of ​​the sampling tube S1 can be very small, and the operational amplifier A1, the adjustment tube T1, the comparator C1 and the like are extremely simple in design. Compared with the sampling resistors that occupy a large chip area and weaken the driving effect in the traditional design, the advantages of the present invention are more obvious.

[0050] In a possible implementation, the resistor R1 is a zero temperature coefficient resistor.

[0051] In a possible implementation, the reference voltage VREF is a zero temperature coefficient voltage.

[0052] The specific working process of the high-precision sampling circuit is described below.

[0053] When the power tube P1 is turned on, the power switch 103 is closed at the same time. At this time, the current IL in the power inductor 102 will flow into the power tube P1 through the power switch 103. The power current in the power tube P1 is the inductor current IL.

[0054] The inductor current IL is calculated according to the following formula:

[0055] IL=Vdc / L*Ton.

[0056] Wherein, Vdc is the voltage value of the voltage source 101, L is the inductance value of the power inductor, and Ton is the conduction time of the power tube P1. According to the above formula, it can be known that the power current increases linearly with the conduction time.

[0057] As the power current IL increases, the drain voltage of the power tube P1 also increases, and the voltage at the positive input terminal of the operational amplifier A1 will be higher than the voltage at the negative input terminal, the output of the operational amplifier A1 will become higher, the conduction capability of the adjustment tube T1 will be enhanced, and the sampling current ISAM will generate a larger current through the adjustment tube T1 to flow into the sampling tube S1, and the drain voltage of the sampling tube S1 will also increase. This change process is that the operational amplifier A1, the adjustment tube T1 and the sampling current form a strong negative feedback path, which will correct the drain voltage of the sampling tube S1 and the power tube P1 in real time, so that the drain voltages of the two are kept consistent in real time.

[0058] Therefore, during the sampling period, the sampling current and power current obtained by the sampling current ISAM are only related to the area ratio of the sampling tube S1 to the power tube P1, and are independent of other states of the sampling tube S1 and the power tube P1, thereby achieving high-precision sampling and eliminating the sampling mismatch caused by the channel length modulation effect.

[0059] When the current sampling ISAM obtains the change of the power current of the power tube P1 in real time, the mirror module M1 mirrors the current sampling ISAM and flows into the resistor R1. The voltage on the resistor is: VR1=ISAM*M*R1, where M is the mirror ratio of the mirror module M1 to the sampling current ISAM.

[0060] When the sampling voltage VR1 on the resistor exceeds the preset reference voltage VREF, that is, the power current flowing into the power tube P1 reaches the preset value, the comparator C1 outputs a signal to turn off the driving unit D1, thereby achieving accurate sampling and control of the power current of the power tube P1.

[0061] The high-precision sampling circuit for source driving provided by the present invention can improve the sampling accuracy of the sampling tube S1 to the power tube P1, and avoid the problem of system instability caused by sampling mismatch, because the current ratio flowing through the sampling tube S1 and the power tube P1 is only related to the area ratio of the two, and has nothing to do with other factors; because the area of ​​the sampling tube S1 is very small, the design of the operational amplifier A1, the comparator C1, etc. is also very simple, which can greatly reduce the design cost of the chip. That is, by introducing a simple negative feedback sampling mode, the present invention can greatly reduce the design cost of the chip while improving the sampling accuracy.

[0062] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A high-precision sampling circuit for source driving, characterized in that: include: Power tube (P1), sampling tube (S1), drive unit (D1), operational amplifier (A1), adjustment tube (T1), mirror module (M1), resistor (R1) and comparator (C1); The sampling tube (S1) is used to perform current fixed ratio sampling on the power tube (P1); The driving unit (D1) is used to control the on and off of the sampling tube (S1), the power tube (P1) and the operational amplifier (A1); The adjustment tube (T1) adjusts the drain potential of the sampling tube (S1) in real time according to the input and output state of the operational amplifier (A1) to ensure that the drain potentials of the sampling tube (S1) and the power tube (P1) are equal during the sampling phase, thereby obtaining a sampling current (ISAM) related to the area ratio; The mirror module (M1) is used to replicate the sampling current (ISAM) and make the sampling current (ISAM) flow through the resistor (R1) to form a sampling voltage; When the sampled voltage exceeds a reference voltage (VREF), the comparator (C1) outputs a signal to control the driving unit (D1) to be turned off.

2. The high-precision sampling circuit according to claim 1, characterized in that: The drain of the power tube (P1) is connected to the power switch 103; the drain of the sampling tube (S1) is connected to the source of the adjustment tube (T1); the gates of the power tube (P1) and the sampling tube (S1) are respectively connected to the driving unit (D1); The driving unit (D1) is also connected to the enable EN of the operational amplifier (A1), the positive input end of the operational amplifier (A1) is connected to the drain of the power tube (P1), the negative input end of the operational amplifier (A1) is connected to the drain of the sampling tube (S1), and the output end of the operational amplifier (A1) is connected to the gate of the adjustment tube (T1); One end of the mirror module (M1) is connected to the drain of the adjustment tube (T1), and the other end is respectively connected to the resistor (R1) and the positive input end of the comparator (C1), the negative input end of the comparator (C1) is connected to the reference voltage (VREF), and the output end of the comparator (C1) is connected to the driving unit (D1).

3. The high-precision sampling circuit according to claim 1, characterized in that: In the sampling phase, the driving unit (D1) controls the sampling tube (S1) and the power tube (P1) to be turned on and off simultaneously, and gives the same driving voltage to the sampling tube (S1) and the power tube (P1).

4. The high-precision sampling circuit according to claim 1, characterized in that: In the sampling phase, the driving unit (D1) controls the on-off of the operational amplifier (A1), so that the operational amplifier (A1), the adjustment tube (T1) and the sampling current (ISAM) form a strong negative feedback modulation path; The two input terminals of the operational amplifier (A1) are forced to be equal under the action of the negative feedback modulation path, so that the drain voltage of the sampling tube (S1) follows the change of the drain voltage of the power tube (P1) in real time and remains consistent.

5. The high-precision sampling circuit according to claim 1, characterized in that: The drain voltage of the power tube (P1) is the product of the power current and the corresponding first on-resistance; the drain voltage of the sampling tube (S1) is the product of the sampling current and the corresponding second on-resistance.

6. The high-precision sampling circuit according to claim 1, characterized in that: The sampling ratio of the sampling current (ISAM) to the power current is the area ratio of the sampling tube (S1) to the power tube (P1).

7. The high-precision sampling circuit according to claim 1, characterized in that: The sampling tube (S1) and the power tube (P1) are devices of the same type and have consistent device characteristic parameters.

8. The high-precision sampling circuit according to claim 1, characterized in that: The sampling tube (S1), the power tube (P1) and the adjustment tube (T1) are all N-type MOS tubes.

9. The high-precision sampling circuit according to claim 1, characterized in that: The resistor (R1) is a zero temperature coefficient resistor.

10. The high-precision sampling circuit according to claim 1, characterized in that: The reference voltage (VREF) is a zero temperature coefficient voltage.

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