A current threshold test circuit and method for a power switch

Abstract

The application belongs to the technical field of switching power supply, and provides a current threshold test circuit and method of power switch, the test circuit comprising a driving circuit, a comparator, a reverse driver, a first power switch and a second power switch connected with the driving circuit respectively; the output ends of the first power switch and the second power switch are connected to form a switching node, the switching node is connected with the negative input end of the comparator, the positive input end of the comparator is connected with a reference voltage, the output end is connected with the input end of the reverse driver, and the output end of the reverse driver is connected with the gate of the second power switch to form a closed loop. The comparator and the reverse driver are configured as an operational amplifier, the current limit threshold test is changed from dynamic test to static test, the threshold measurement accuracy and the measurement speed are greatly improved, the test efficiency is improved, sudden shutdown of the power tube under large current condition is avoided, and damage to the device and the automatic test machine is reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of switching power supply, more particularly relates to a current threshold test circuit and method of power switch. BACKGROUND

[0002] Switching power supply is widely used in power supply system due to its high conversion efficiency. The power tube in switching power supply needs a driving circuit to turn on or turn off. Common topologies include buck, boost, buck-boost, etc.

[0003] The turn-on speed of the switching tube has a direct impact on the system reliability and system conversion efficiency. In order to improve the reliability of the system, the switching power supply circuit generally integrates the over-current protection function. Figure 1 Figure 1 is an equivalent circuit of a prior art buck switching power supply with over-current protection function, as shown in Figure 1, M1 and M2 are power switches, the reference voltage REF and the comparator CMP1 constitute an over-current protection circuit. When the current through M1 is greater than the set threshold REF, the SW node voltage is lower than REF, and the OC output is a high signal, so that M1 is turned off through the drive control circuit, thereby achieving the purpose of over-current protection. Figure 1

[0004] The over-current protection threshold of the power switch M1 cannot be too high or too low. If it is too high, it cannot achieve the purpose of protecting the device, and if it is too low, it will not be able to provide normal output. Therefore, before the device is shipped, the over-current protection threshold needs to be tested by using an automated test machine to check whether the index meets the requirements.

[0005] Figure 2 Figure 2 is a prior art power switch over-current protection threshold measurement circuit diagram, as shown in Figure 2, a programmable current source ISW is added to the switching node SW end. When the ISW current is less than the over-current protection threshold of the transistor M1, M1 is turned on, and the ISW current is gradually increased. When the ISW current reaches the over-current protection threshold, M1 is turned off, and the current at SW becomes low. At this time, the ISW current is recorded to obtain the over-current protection threshold. The scheme has the following problems: Figure 2 1. When the ISW current reaches the over-current protection threshold, M1 is suddenly turned off, and SW quickly changes from near VDD level to near ground level. This rapid change can easily damage the device and also easily damage the automated test machine.

[0006] 2. Since the ISW current cannot change linearly, but changes in steps, the test time is long, which greatly reduces the test efficiency.

[0007] SUMMARY

[0008] (1) Technical problem to be solved​​

[0009] The present application aims to solve the technical problem of how to reduce damage to the device while improving the efficiency and accuracy of the device current limit threshold test.

[0010] (II) Technical solutions

[0011] To solve the above technical problems, one aspect of the present application provides a current threshold test circuit for power switch, which is used for testing the power tube current threshold of the power switch, and the test circuit comprises a driving circuit, a comparator, a reverse driver, a first power switch and a second power switch connected with the driving circuit respectively;

[0012] The output ends of the first power switch and the second power switch are connected to form a switch node, the switch node is connected with the negative input end of the comparator, the positive input end of the comparator is connected with a reference voltage, the output end is connected with the input end of the reverse driver, and the output end of the reverse driver is connected with the gate of the second power switch to form a closed loop.

[0013] According to the preferred embodiment of the present application, the first power switch and the second power switch are both NMOS tubes.

[0014] According to the preferred embodiment of the present application, driving signal switches are arranged between the driving circuit and the first power switch and the second power switch respectively, and the gate of the first power switch is disconnected from the driving circuit and connected with a high level.

[0015] According to the preferred embodiment of the present application, the gate of the second power switch is disconnected from the driving circuit and connected with the output end of the reverse driver, so that the second power switch is always in the on state.

[0016] According to the preferred embodiment of the present application, the output end of the comparator is connected with the input end of the reverse driver to form an operational amplifier, so that when the voltage of the positive input end and the negative input end of the comparator is equal, the voltage at the switch node is equal to the reference voltage.

[0017] According to the preferred embodiment of the present application, the positive input end and the negative input end of the comparator form the input end of the operational amplifier, and the reverse driver forms the second amplification stage of the operational amplifier.

[0018] According to the preferred embodiment of the present application, when the voltage at the switch node is equal to the reference voltage of the comparator, the current at the first power switch is the current threshold.

[0019] The second aspect of the present application provides a current threshold test method for power switch, characterized in that it comprises:

[0020] Power on the test circuit described above;

[0021] Connect the gate of the first power switch to high level, while keeping the second power switch in the on state;

[0022] When the voltage at the switch node is equal to the reference voltage, the current of the first power switch is measured, which is the current threshold of the first power switch.

[0023] (Three) beneficial effects

[0024] The present application changes the current limit threshold test from dynamic test to static test by configuring the comparator and the inverter driver as an operational amplifier, greatly improves the threshold measurement accuracy and measurement speed, thus improves the test efficiency, and at the same time avoids the sudden shutdown of the power tube under the condition of large current, reduces the damage to the device and the automatic test machine. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Is the equivalent circuit of the power stage of an existing step-down switching power supply with overcurrent protection function.

[0026] Figure 2 Is a power switch overcurrent protection threshold measurement circuit diagram.

[0027] Figure 3 Is a power switch overcurrent protection threshold measurement method signal diagram.

[0028] Figure 4 Is a comparator circuit diagram.

[0029] Figure 5 Is a power switch overcurrent protection threshold measurement circuit diagram of an embodiment of the present application.

[0030] Figure 6 Is a comparator and inverter driver circuit diagram of an embodiment of the present application.

[0031] Figure 7 Is a power switch overcurrent protection threshold measurement simulation diagram using the scheme of the present application.

[0032] Figure 8 Is a power switch overcurrent protection threshold test method flowchart of the present application. EMBODIMENT

[0033] In the introduction process for specific embodiments, the structural, performance, effect or other characteristic details are described in order to make the embodiments fully understood by those skilled in the art. However, it does not exclude that those skilled in the art can implement the present application without the above-mentioned structure, performance, effect or other characteristics in specific cases.

[0034] The flowcharts in the drawings are only exemplary flow demonstrations, and do not mean that all the contents, operations and steps in the flowcharts must be included in the scheme of the present application, nor mean that the execution order shown in the flowcharts must be executed. For example, some operations / steps in the flowcharts can be decomposed, some operations / steps can be combined or partially combined, etc. The execution order shown in the flowcharts can be changed according to actual conditions without departing from the inventive concept of the present application.

[0035] The blocks in the drawings Figure 1 Generally represent functional entities, and do not necessarily correspond to physically independent entities. That is, these functional entities can be implemented in software form, or implemented in one or more hardware modules or integrated circuits, or implemented in different network and / or processing unit devices and / or microcontroller devices.

[0036] The same reference signs in the various drawings represent the same or similar elements, components or parts, and thus the repeated description of the same or similar elements, components or parts can be omitted hereinafter. It should also be understood that although the first, second, third, etc. representative numerals are used to describe various devices, elements, components or parts in the present application, these devices, elements, components or parts should not be limited by these representative numerals. That is, these representative numerals are only used to distinguish one from another. For example, the first device can also be referred to as the second device without departing from the essential technical scheme of the present application. In addition, the terms "and / or", "and / or" mean all combinations of the listed items.

[0037] In the prior art, the method for measuring the over-current protection threshold of a power switch is to apply a programmable current source ISW to the switch node SW. When the current of ISW is less than the over-current protection threshold, the first power switch M1 is turned on, and the current of ISW is gradually increased. When the current of ISW reaches the over-current protection threshold, M1 is turned off, and SW becomes low. When the voltage of SW is equal to the voltage of REF, OC flips, and at this time the current threshold IOC is equal to the current of ISW, that is, the over-current protection threshold is obtained.

[0038] Figure 3 is a signal schematic diagram of a prior art method for measuring the over-current protection threshold of a power switch, as Figure 3 shown, the above method has the following defects: the current of ISW cannot change linearly, but changes in steps.

[0039] In order to improve the measurement accuracy, it is necessary to reduce the current change of each time, that is, the height of Istep in the figure; and in order to shorten the test time, it is necessary to reduce the number of current changes and the time of each step as much as possible. Assuming that the current limit threshold is 10A and the measurement accuracy is 1%, Istep is 10A*1%=0.1A at most, so 100 steps are needed, and assuming that the time required for each step is 2ms, the total time required is 200ms. In general, Istep needs to be much smaller than 1% to achieve 1% accuracy. Therefore, the test time of only this item is more than 200ms, which greatly reduces the test efficiency.

[0040] To solve the above technical problems, the application provides a current threshold test circuit of a power switch, wherein a comparator and an inverter driver are configured as an operational amplifier, and current limit threshold test is changed from dynamic test to static test, so that the threshold measurement accuracy and speed are greatly improved.

[0041] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with specific embodiments and with reference to the drawings.

[0042] Figure 5 is a power switch overcurrent protection threshold measurement circuit diagram of an embodiment of the application, as Figure 5 shown,

[0043] The test circuit comprises driving circuits DRV1 and DRV2, a comparator CMP1, an inverter driver, a first power switch M1 and a second power switch M2 connected with the driving circuits respectively;

[0044] The output ends of the first power switch M1 and the second power switch M2 are connected to form a switch node SW, the switch node SW is connected with the negative input end of the comparator CMP1, the positive input end of the comparator CMP1 is connected with a reference voltage REF, the output end is connected with the input end of the inverter driver, and the output end of the inverter driver is connected with the gate of the second power switch M2 to form a closed loop.

[0045] Preferably, the first power switch M1 and the second power switch M2 are both NMOS tubes, the first power switch M1 can also be selected as a PMOS tube, or the first power switch M1 and the second power switch M2 can also be selected as a triode.

[0046] The driving circuits and the first power switch M1 and the second power switch M2 are respectively provided with driving signal switches TM, the gate of the first power switch M1 is disconnected with the driving circuit and connected with a high level M1G. The gate of the second power switch M2 is disconnected with the driving circuit and connected with the output end M2G of the inverter driver, so that the second power switch M2 is always in an on state.

[0047] Figure 4 is a prior art comparator circuit diagram, as shown in Figure 4 Transistors MP1, MP2, MP3 and BIAS constitute a current source bias. Transistors MN1 and MN2 constitute the input of the comparator, and MN3 constitutes the second stage of the comparator. OC is the output signal of the comparator.

[0048] Figure 6 is a comparator and inverter circuit diagram of an embodiment of the present application, as shown in Figure 6 On the basis of the prior art comparator circuit, an inverter is added, which together constitutes an operational amplifier. MN1 and MN2 still constitute the input of the operational amplifier, so the input offset voltage of the operational amplifier is basically the same as that of the comparator CMP1. The inverter includes transistors MN4, MP4, MP5 and R1, which constitute the second stage of amplification. C1 is used as a loop compensator to keep the loop stable.

[0049] When the voltage at the switch node SW is higher than the reference voltage REF of the comparator, the first power switch M1 is turned on;

[0050] When the voltage at the switch node SW is lower than the reference voltage REF of the comparator, the first power switch M1 is turned off;

[0051] When the voltage at the switch node SW is equal to the reference voltage REF of the comparator, the comparator is in a virtual short state, and the current at the first power switch M1 is a limit threshold current, the specific principle being as follows:

[0052] According to the working principle of the operational amplifier, in a stable state, the comparator is in a virtual short state, and the voltage at the switch node SW will be equal to the voltage REF. In combination with Figure 3 At this time, the first power switch current threshold IOC*RM1=VDD-REF. Since the voltage SW=REF, the voltage at M1 is equal to the product of the current and RM1, and also equal to VDD-SW=VDD-REF. Therefore, it is deduced that the current at M1 at this time is equal to IOC, that is, the current threshold. Therefore, the current limit threshold can be measured by measuring the current in M1 under static conditions (i.e., the current on VDD).

[0053] This embodiment only lists a step-down voltage converter, and the principle can also be applied to step-up, step-up / down, and other occasions requiring dynamic measurement of the current limit threshold.

[0054] Figure 7 is a simulation diagram for measuring the power switch overcurrent protection threshold using the scheme of the present application, as shown in Figure 7As shown, by using the static test method proposed in the application, it can be seen from the following simulation results that the time for M1 current to reach steady state is less than 0.1 ms. The error of SW voltage and REF voltage depends on the total gain formed by the operational amplifier + inverting driver + power switch M2 amplification stage, which is generally much larger than 1000 times. According to the calculation of the gain of 1000, the error of SW voltage and REF voltage is less than 0.1% (1 / 1000), that is, the error of the current in M1 and the set current limit value is less than 0.1% in steady state, which is obviously better than the dynamic test method in the prior art.

[0055] Figure 8 is a flow chart of the power switch overcurrent protection threshold test method of the application, as Figure 8 shown, the application further proposes a current threshold test method for a power switch, comprising:

[0056] Power on the test circuit in the above embodiment;

[0057] Connect the gate of the first power switch to high level, while keeping the second power switch in the on state;

[0058] When the voltage at the switch node is equal to the reference voltage, the current of the first power switch is measured, which is the current threshold of the first power switch.

[0059] The application greatly improves the threshold measurement accuracy and measurement speed by configuring the comparator and the inverting driver into an operational amplifier, changes the current limit threshold test from dynamic test to static test, thus improves the test efficiency, and at the same time avoids the sudden shutdown of the power tube under large current, reduces the damage to the device and the automatic test machine.

[0060] Those skilled in the art can understand that all or part of the steps of the above embodiments are realized as programs (computer programs) executed by computer data processing equipment. When the computer program is executed, the above-mentioned method provided by the application can be realized. Moreover, the computer program can be stored in a computer readable storage medium, which can be a readable storage medium such as a disk, an optical disk, a ROM, a RAM, etc. It can also be a storage array composed of multiple storage media, such as a disk or tape storage array. The storage medium is not limited to centralized storage, and it can also be distributed storage, such as cloud storage based on cloud computing.

[0061] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the present application is not inherently related to any specific computer, virtual device or electronic equipment, and various general-purpose devices can also implement the present application. The above-described is only a specific embodiment of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A current threshold test circuit of a power switch for testing a power tube current threshold of a power switch, characterized by, The test circuit comprises a driving circuit, a comparator, a reverse driver, a first power switch and a second power switch connected with the driving circuit respectively; The output terminals of the first power switch and the second power switch are connected to form a switch node, the switch node is connected with the negative input terminal of the comparator, the positive input terminal of the comparator is connected with a reference voltage, the output terminal is connected with the input terminal of the reverse driver, and the output terminal of the reverse driver is connected with the gate of the second power switch to form a closed loop.

2. The current threshold test circuit for a power switch according to claim 1, characterized in that, The first power switch and the second power switch are both NMOS tubes.

3. The current threshold test circuit for a power switch of claim 2, wherein, The driving circuit is provided with a driving signal switch between the driving circuit and the first power switch and the second power switch, the gate of the first power switch is disconnected with the driving circuit and connected with a high level.

4. The current threshold test circuit for a power switch of claim 3, wherein, The gate of the second power switch is disconnected with the driving circuit and connected with the output terminal of the reverse driver, so that the second power switch is always in an on state.

5. The current threshold test circuit for a power switch of claim 4, wherein, The output terminal of the comparator is connected with the input terminal of the reverse driver to form an operational amplifier, so that when the voltage of the positive input terminal and the negative input terminal of the comparator is equal, the voltage at the switch node is equal to the reference voltage.

6. The current threshold test circuit for a power switch of claim 5, wherein, The positive input terminal and the negative input terminal of the comparator form the input terminal of the operational amplifier, and the reverse driver forms the second amplification stage of the operational amplifier.

7. The current threshold test circuit for a power switch of claim 5, wherein, When the voltage at the switch node is equal to the reference voltage of the comparator, the current at the first power switch is a current threshold.

8. A method of testing a current threshold of a power switch, characterized by, Comprise: Power on the test circuit as claimed in any one of claims 1-7; Connect the gate of the first power switch with a high level while keeping the second power switch in an on state; When the voltage at the switch node is equal to the reference voltage, the current of the first power switch is the current threshold of the first power switch.

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