Design of a medium-scale integrated circuit functional tester

Integrated circuit testing technology has developed along 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 ultra-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 according to the test categories. The tester products on the market currently have relatively simple functions and are very expensive, which brings inconvenience to the testing and maintenance of circuits. Therefore, it is of great practical value to research and develop simple, fast, and intelligent integrated circuit testers [1-2].

In the electronic experiment teaching of colleges and universities, medium-scale integrated circuits such as analog-to-digital converters (ADC), digital-to-analog converters (DAC), 555 integrated timing circuits, and 3524 switching power supply controllers are often used. Since students usually use chips for the first time, they often damage or destroy circuit chips due to improper operation, but they cannot make correct judgments on the surface. In this case, it is very necessary to have a suitable integrated circuit tester to test and judge the quality of the chip. However, there are no suitable testers available on the market. Therefore, this paper designs and produces a tester that can be used for some specific medium-scale circuits. According to specific needs, several chips such as ADC0809, DAC0832, LM555, and WC3524 were selected as test objects, and corresponding special testers were designed.

The structural schematic diagram of the tester is shown in Figure 1. The controller of the tester uses Atmel's 8-bit single-chip microcomputer 89C55 to complete the interface management and automatic detection control functions [3]. Maxim's MAX197 high-precision A/D converter is used to complete the analog signal test [4]. The test principles and methods of various devices are introduced below.

1 Test Principle and Test Circuit

To test the function or characteristic parameters of a device, a typical application circuit of the device is usually used to demonstrate the function and reflect the parameter value directly or indirectly.

1.1 Test of analog-to-digital converter ADC0809

The test circuit diagram of 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, which is also sent to MAX197. The controller selects one analog channel of ADC0809 and sends a start conversion signal to start ADC0809 conversion, and then controls MAX197 to start conversion. Wait for the conversion to end, read the conversion results of the two respectively, and compare the values ​​to determine whether the device function is normal according to the error limit. Change the channel to continue testing until the 8 channels are tested and the results are displayed.

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1.2 DAC0832 Test

The D/A converter DAC0832 is an 8-bit binary digital-to-analog converter. The 8 digital input terminals are DI7~DI0, where DI7 is the MSB and DI0 is the LSB. Its analog output terminals are current outputs IOUT1 and IOUT2. When the input digital quantity is the largest, the current output of IOUT1 is the largest; when the input digital quantity is zero, the output current is the smallest. The current output of IOUT2 ​​is just the opposite. These two terminals can be connected to an external operational amplifier to achieve current/voltage conversion. There is also a feedback resistor inside this chip, which can be used as a feedback resistor for an external operational amplifier. The DAC0832 test schematic is shown in Figure 3. There are two levels of input registers in the chip, which enable it to have three input modes: double buffering, single buffering and direct pass-through, to meet the needs of various circuits, such as requiring multi-channel D/A asynchronous input, synchronous conversion, etc.

The single-chip microcomputer transmits an 8-bit binary digital quantity to DAC0832, and when the write control and chip select control of the two-level buffer are both valid, the D/A conversion begins, and the conversion speed is in the microsecond level. After the digital-to-analog conversion, the output current is converted into a voltage through the operational amplifier, and the voltage is converted into a digital quantity through MAX197 and read back to the single-chip microcomputer, and then compared with the original output digital quantity to determine whether the chip under test is normal or not.

1.3 Testing the 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 method, which is used to test whether the two internal comparators and RS trigger are normal, and at the same time, it can test whether the control voltage is normal.

The microcontroller outputs a negative pulse to the second pin of the LM555 chip, triggering the timing circuit. The microcontroller reads the output signal of the timing circuit to determine whether the corresponding rising and falling edges appear, thereby determining whether the chip functions normally.

1.4 Testing of SG3524

The internal block diagram of SG3524 is shown in Figure 5. The input DC power supply UIN enters from pin 15 and is divided into two paths: one path is used as the power supply for the amplifier, comparator, oscillator, logic circuit and control circuit; the other path is used as a reference voltage source to generate a +5 V reference voltage output to pin 16 as an external voltage reference. The timing capacitor CT and the timing resistor RT are connected to pins 7 and 6 of the oscillator part to obtain the required oscillation frequency. The SG3524 test schematic is shown in Figure 6, which 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 ratio coefficient. The microcontroller can determine the quality of the SG3524 chip by measuring the pulse frequency on pin 3 and the voltage at the output end through MAX197. The test of the overcurrent protection function is not considered for the time being. [page]

2 Operation and software structure

The basic working process of the tester is as follows: after the power is turned on, the power indicator light is on, indicating that the power is working properly, and the display shows the waiting test information, indicating that the test operation can be started. Press key 1 to select the chip to be tested, and the chip model where the cursor stops indicates that it is the current chip to be tested. Each time the selection key is pressed, the cursor points to the next model, and the key can be pressed repeatedly to select. When the cursor moves to the chip to be tested, press the confirmation key 2, and then the microcontroller controls and starts to automatically test the chip. At this time, the indicator light corresponding to the chip is on; then the external circuit or microcontroller gives the chip to be tested a certain analog or digital input quantity, which is processed by MAX197 (or directly sent to the microcontroller) after passing through the test circuit of each chip, 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 light is always on, and the LCD display shows OK; otherwise, the chip is wrong, the test indicator light flashes, and the LCD display shows BAD. After the chip is tested, press the reset key 3 to return to the initial state and the next round of testing can be carried out. The software flow chart is shown in Figure 7.

The experimental prototype was used by teachers and students, and the test results were very ideal. The test accuracy rate can reach more than 90%, which provides convenience for teaching.