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In the teaching of electronic experiments in colleges and universities, medium-scale integrated circuits such as analog-to-digital converters (ADCs), digital-to-analog converters (DACs), 555 integrated timing circuits, and 3524 switching power supply controllers are often used. Because students are usually in contact with the chip for the first time, the circuit chip is often damaged or damaged due to improper operation, but it is impossible to make a correct judgment on the surface. In this case, there is a great need for an appropriate integrated circuit tester to test and judge the quality of the chip. There is no suitable tester on the market for purchase. Therefore, this paper designs and manufactures a tester that can be used for some specific medium-scale circuits. According to the specific needs of the selected ADC0809, DAC0832, LM555, WC3524 and other chips as a test object, and designed a corresponding special tester.
The schematic block diagram of the tester is shown in Figure 1. The controller of the test instrument adopts the eight-bit microcontroller 89C55 of Atmel Company, which is used to complete the interface management and automatic detection control function [3]. Maxim's MAX197 high-precision A/D converter was used to complete the analog signal test [4]. The following introduces the test principles and methods of various types of devices. 
1 Test principle and test circuit Test a function or characteristic parameter of a device, usually adopt the typical application circuit of this device, reflect the function, reflect the parameter value directly or indirectly.
1.1 Analog-to-digital converter ADC0809 test ADC ADC0809 test circuit shown in Figure 2. According to the test circuit, ADC0809 8 channels input the same analog quantity, this analog quantity also feeds MAX197. The controller selects one analog channel of the ADC0809 and issues a start conversion signal so that the ADC0809 starts conversion and then controls the MAX197 to start conversion. Wait for the end of the conversion, read the conversion results of both, and compare the values. Determine whether the device function is normal based on the error limit. Change the channel to continue testing until the 8 channels are tested and the result is displayed. 
1.2 Test of DAC0832 D/A Converter DAC0832 is an 8-bit binary digital-analog converter. The 8 digital inputs are DI7~DI0, respectively, where DI7 is MSB and DI0 is LSB. Its analog output terminals are current outputs IOUT1 and IOUT2. When the input digital quantity is the maximum, the output current of IOUT1 is the largest; when the input digital quantity is zero, the output current is the minimum. The current output at the IOUT2 ​​is the opposite. These two terminals can be connected to an external op amp for current/voltage conversion. There is also a feedback resistor inside this chip, which can be used as the feedback resistor of the external operational amplifier. The DAC0832 test schematic is shown in Figure 3. There are two levels of input registers in the chip, so that it has three input methods: double buffering, single buffering and pass-through, which are suitable for various circuit needs, such as requiring multiple D/A asynchronous inputs, synchronous conversion, and the like. 
1.3LM555 Timing Circuit Test The integrated timing circuit LM555 is widely used. The test circuit is shown in Figure 4. This is a typical timing circuit connection, which is used to test whether the internal two comparators and RS flip-flops are normal and whether the control voltage is normal. 
The microcontroller outputs a negative pulse to pin 2 of the LM555, triggering the timing circuit. The microcontroller reads the output signal of the timing circuit to determine whether there is a corresponding rising edge or falling edge, so that the function of the chip can be judged to be normal or not.
1.4 SG3524 Test The internal block diagram of the SG3524 is shown in Figure 5. The input DC power supply UIN is divided into two paths from pin 15: one as the power supply for the amplifier, comparator, oscillator and logic circuit and control circuit; the other as the reference voltage source generates the +5V reference voltage output to pin 16 as the external Voltage reference. On pin 7 and pin 6 of the oscillator part, a timing capacitor CT and a timing resistor RT are externally connected to obtain the desired oscillation frequency. SG3524 test schematic diagram shown in Figure 6, connected into a typical step-down switching power supply circuit, the use of error amplifier voltage negative feedback. By changing the sampling ratio factor, the output voltage can be changed. By reading the pulse frequency on pin 3 and measuring the output voltage through the MAX197, the MCU can determine the quality of the SG3524 chip. The test of the overcurrent protection function was not considered during the test. 
The experimental prototype is used by teachers and students. The test effect is very satisfactory. The test accuracy rate can reach more than 90%, which provides convenience for teaching.
The test technology of integrated circuits develops with the rapid development of integrated circuit development and application. Integrated circuit testers have also evolved from initially testing small-scale integrated circuits to testing mid-scale, large-scale, and very-large-scale integrated circuits. Integrated circuit tester can be divided according to test categories: digital integrated circuit tester, memory tester, analog and mixed signal circuit tester, online test system and verification system. At present, the tester products on the market are relatively single-function, and the price is very expensive, which brings inconvenience to the testing and maintenance of the circuit. Therefore, the research and development of a simple and rapid integrated circuit tester with a certain degree of intelligence has a very high practical value [1-2]. When the 8-bit binary digital data is sent to the DAC0832 by the single-chip microcomputer, the two-stage buffering write control and chip select control are all valid, and the D/A conversion is started, and the conversion speed is in microseconds. After digital-to-analog conversion, the output current is converted into a voltage by the op amp. The voltage is converted back to the microcontroller through the MAX197 and then compared with the original output digital value to determine whether the chip under test is normal or not. 2 Operation and Software Structure The basic workflow of the tester is: After the power is turned on, the power indicator is on, indicating that the power supply is working properly, and the display shows waiting for test information, indicating that the test operation can be started. The chip to be tested is selected by the button 1, and the chip type indicating the cursor stays is the current chip to be tested. Each time you press the Select key, the cursor points to the next model, and you can cycle through the selection by pressing the key repeatedly. When the cursor moves to the chip to be tested, the OK button 2 is pressed. Next, the chip is controlled by the SCM. The chip is automatically tested. At this time, the LED corresponding to the chip is turned on; then, an external circuit or a microcontroller is used to simulate the chip to be tested. Or digital input, after each chip's test circuit, through the MAX197 for processing (or directly to the microcontroller), and the microcontroller pre-stored standard values ​​for comparison. If the test value is within a certain range around the standard value, the chip is normal, the test indicator light is on, and the LCD display is OK; otherwise, the chip is in error, the test indicator flashes, and the LCD displays BAD. After this chip is tested, press the reset button 3 to return to the initial state and proceed to the next round of testing. Software flow chart shown in Figure 7.