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“The testing technology of integrated circuits develops with the rapid development of integrated Circuit development and application. Integrated circuit testers have also developed from initially testing small-scale integrated circuits to testing medium-scale, large-scale and very large-scale integrated circuits. Integrated circuit testers can be divided into: digital integrated circuit testers, memory testers, analog and mixed-signal circuit testers, online test systems and verification systems.
The testing technology of integrated circuits develops with the rapid development of integrated circuit development and application. Integrated circuit testers have also developed from initially testing small-scale integrated circuits to testing medium-scale, large-scale and very large-scale integrated circuits. Integrated circuit testers can be divided into: digital integrated circuit testers, memory testers, analog and mixed-signal circuit testers, online test systems and verification systems. At present, the functions of the tester products on the market are relatively single, and the price is very expensive, which brings inconvenience to the testing and maintenance of the circuit. Therefore, the research and development of simple, quick and intelligent integrated circuit tester has high practical value.
In the Electronic experiment teaching of colleges and universities, medium-scale integrated circuits such as analog-to-digital converter (ADC), digital-to-analog converter (DAC), 555 integrated timing circuit, and 3524 switching power supply controller are often used. Because students usually use 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, it is very necessary to have an appropriate integrated circuit tester for testing and judging the quality of the chip. And there is no suitable tester available on the market. Therefore, this paper designs and manufactures a tester that can be used for some specific medium-scale circuits. According to specific needs, several chips such as ADC0809, DAC0832, LM555, WC3524 are selected as test objects, and corresponding special testers are designed.
The schematic block diagram of the structure 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 and control functions. Which uses Maxim’s MAX197 high-precision A/D converter to complete the analog signal test. The test principles and methods of various types of devices are described below.
1 Test principle and test circuit
To test the function or characteristic parameters of a device, the typical application circuit of the device is usually adopted, the function is reflected, and the parameter value is directly or indirectly reflected.
1.1 Test of analog-to-digital converter ADC0809
The test circuit diagram of the analog-to-digital converter ADC0809 is shown in Figure 2. According to the test circuit, the 8 channels of ADC0809 input the same analog quantity, and the analog quantity is also sent to MAX197. The controller selects 1 analog channel of ADC0809, and sends out a start conversion signal to make ADC0809 start conversion, and then control MAX197 to start conversion. Wait for the conversion to end, read the conversion results of the two, and compare the values to determine whether the device functions normally according to the error limit. Change the channel and continue the test until the 8 channels are tested, and the result is displayed.
1.2 Test of DAC0832
The D/A converter DAC0832 is an 8-bit binary digital-to-analog converter. The 8 digital input terminals are DI7~DI0, of which DI7 is MSB and DI0 is LSB. Its analog output terminals are current output IOUT1 and IOUT2. When the input digital quantity is the largest, the output current of the IOUT1 terminal is the largest; when the input digital quantity is zero, the output current is the smallest. The current output at IOUT2 is just the opposite. These two terminals can be connected to an external operational amplifier to realize current/voltage conversion. There is also a feedback resistor inside the chip, which can be used as a feedback resistor for an external operational amplifier. The test schematic diagram of DAC0832 is shown in Figure 3. There are two levels of input registers in the chip, so that it has three input modes: double buffer, single buffer and pass-through, so as to be suitable for the needs of various circuits, such as requiring multiple D/A asynchronous inputs and synchronous conversion.
A single 8-bit binary digital quantity is sent to the DAC0832 by the single-chip microcomputer, so that when the write control and chip selection control of the two-level buffer are effective, the D/A conversion is started, and the conversion speed is microsecond level. After digital-to-analog conversion, the output current is converted into a voltage by an operational amplifier, and the voltage is converted into a digital quantity by MAX197 and read back to the microcontroller, and then compared with the original output digital quantity to judge whether the tested chip is normal or not.
1.3 Test of LM555 timing circuit
The application of the integrated timing circuit LM555 is very wide, and its test circuit is shown in Figure 4. This is a typical timing circuit connection, which is used to test whether the internal 2 comparators and RS flip-flops are normal, and can test whether the control voltage is normal.
The single-chip microcomputer outputs a negative pulse to the second pin of the LM555 chip to trigger the timing circuit. The single-chip microcomputer reads the output signal of the timing circuit to determine whether the corresponding rising edge and falling edge occur, so as to judge whether the function of the chip is normal or not.
1.4 Test of SG3524
The internal block diagram of SG3524 is shown in Figure 5. The input DC power UIN enters from pin 15 and is divided into 2 channels: one channel is used as the power supply of amplifier, comparator, oscillator, logic circuit and control circuit; the other channel is used as a reference voltage source to generate +5 V reference voltage and output to pin 16 as External Voltage Reference. Connect the timing capacitor CT and timing resistor RT to pins 7 and 6 of the oscillator part to obtain the required oscillation frequency. The test schematic diagram of SG3524 is shown in Figure 6. It is connected into a typical step-down switching power supply circuit, and the error amplifier is used to form a voltage negative feedback. The output voltage can be changed by changing the sampling scale factor. The single chip can judge the quality of the SG3524 chip by measuring the pulse frequency on pin 3 and measuring the voltage at the output end through MAX197. The test of the overcurrent protection function is not considered in the test for the time being.
2 Operation and software structure
The basic work flow of the tester is: after the power is turned on, the power indicator light is on, indicating that the power supply is working normally, and the Display shows the waiting test information, indicating that the test operation can be started. Press button 1 to select the chip to be tested, and the Model of the chip where the cursor is displayed indicates that it is the current chip to be tested. Each time you press the selection key, the cursor points to the next model, and you can cycle through the selection by pressing the key continuously. When the cursor moves to the chip to be tested, press the OK key 2, and then it is controlled by the single-chip microcomputer to automatically test the chip. At this time, the indicator light corresponding to the chip is on; Or digital input quantity, after passing through the test circuit of each chip, it is processed by MAX197 (or directly sent to the microcontroller), and compared with the standard value pre-stored in the microcontroller. If the test value is within a certain range near the standard value, the chip is normal, the test indicator is always on, and the LCD displays OK; otherwise, the chip is faulty, the test indicator flashes, and the LCD displays BAD. After the chip test is completed, press the reset button 3 to return to the initial state, and the next round of testing can be performed. The software flow chart is shown in Figure 7.
The experimental prototype is used by teachers and students, and the test effect is very ideal. The test accuracy rate can reach more than 90%, which provides convenience for teaching.