When it is necessary to replace IC chip in PCB circuit design, let me talk about my skills of replacing IC chip to help designers improve the PCB circuit design.
Two skills of IC replacement
First, direct substitution
Direct substitution refers to directly replacing the original IC with other IC chips without making any changes, and the main functions and indexes of the machine will not be affected after substitution.
The replacement criterion is that the function, function index, packaging mode, pin use, pin serial number and distance of the replacement IC are the same. During this period, the same IC function not only means the same function, but also means the same logic polarity, that is, the polarity of output and input levels, voltage and current fluctuations must be the same. Functional index refers to the primary electrical parameters (or primary characteristic curve), maximum dissipation power, maximum working voltage, frequency scale and input and output impedance of each signal of the integrated circuit should be close to the original integrated circuit. For low-power replacement parts, the radiator should be enlarged.
1, replacing the same type of IC chip.
The substitution of the same type of IC chip is generally reliable. When the equipment is integrated with PCB circuit, pay attention to the direction, and don't make a mistake, otherwise the integrated PCB circuit is likely to be burned when it is powered on. Some single in-line amplifier IC have the same type, function and characteristics, but the direction of pin arrangement order is different. For example, the dual-channel power amplifier ICLA4507 has "positive" and "negative" pins, and its initial pin labels (color dots or color pits) have different directions: IC with suffix "R" without suffix, such as M5 1 15P and M51/5rp.
2. Substitution of different types of integrated circuits
The replacement of (1) type integrated circuits has the same prefix letters and different numbers. This substitution can also be directly substituted for each other, as long as their pin functions are exactly the same, and the internal PCB circuit and electrical parameters are slightly different. For example, the audio plays IC LA 1363 and LA 1365. The latter adds a zener diode inside the fifth pin of the IC, and everything else is the same.
(2) IC replacement with different prefix letters and the same number. Generally speaking, prefix letters indicate manufacturers and categories of PCB circuits. The numbers after the prefix letters are the same, and most of them can be directly replaced. However, although the numbers are the same, the functions are completely different. For example, HA 1364 is an audio IC, and uPC 1364 is a color decoding IC; 4558, pin 8 is an operational amplifier NJM4558, and pin 14 is a digital PCB circuit of CD4558; So there is no substitute for the two.
(3) Replace IC with letters and numbers with different prefixes. Some manufacturers introduce unpacked IC chips and then process them into products named after our factory. There are also products that have been improved to improve certain parameters. These products are usually named by different types or distinguished by type suffixes. For example, AN380 and uPC 1380 can be directly replaced; AN5620, TEA5620, DG5620, etc. Can be directly substituted.
Second, indirect substitution.
Indirect substitution refers to the method of slightly modifying the peripheral PCB circuit of an IC that cannot be directly replaced, changing the original pin layout or adding or subtracting a single component to make it a replaceable IC.
Substitution standard: the IC used for substitution can have different functions and shapes from the original IC pins, but the functions should be the same and the characteristics should be similar; The function of the original machine should not be affected after replacement.
1. Replacement of integrated circuit chips with the same plastic type but different pin functions
This replacement needs to change the peripheral PCB circuit and pin layout, so it needs certain theoretical knowledge, complete information and rich practical experience and skills.
2. Replace the lC chip with the same PCB circuit function but different single pin function.
It can be replaced according to the detailed parameters and descriptions of various types of IC. If there is a difference between the positive and negative polarity of AGC and video signal output in TV, an inverter can be added at the output end instead. Baineng Com, a subsidiary of Ji Qin Group, is the first service channel in the electronic industry in China, providing complete solutions for the supply chain of electronic industry, such as components, sensor procurement, PCB customization, BOM distribution and material selection, to meet the comprehensive needs of small and medium-sized customers in the electronic industry in one stop.
3. Don't ground some empty feet privately.
Some pins in the internal equivalent PCB circuit and the circuit using PCB are not marked. When encountering an empty needle, don't ground it privately. These pins are replacement or spare pins and are sometimes used as internal connections.
4. Replace integrated circuit chips with different packages.
The same type of IC chip, but with different package shapes, can be replaced only by reshaping the pins of the new device according to the shape and placement of the pins of the original device. For example, AFTPCB circuits CA3064 and CA3064E, the former has a circular package and radial pins; The latter is a dual in-line plastic package, which has the same internal characteristics and can be connected according to the pin function. Double-row ICAN7 1 14, AN7 1 15 are basically the same as LA4 100 and LA4 102, and the difference between the pins and the heat sink is just 180 degrees. As mentioned above, the AN5620 with heat sink is packaged with 16 pin, the TEA5620 is packaged with 18 pin, and the pins 9 and 10 are located on the right side of the integrated PCB circuit, which is equivalent to the heat sink of the AN5620. The other pins of AN5620 are placed in the same way, and pins 9 and 10 can be used by grounding.
5. Combination substitution
Combination substitution is a method to recombine the undamaged PCB circuit parts in multiple ICs of the same type into a complete IC to replace the dysfunctional IC. It is very suitable for the situation that you can't buy the original IC. However, it is required that the complete PCB circuit in the IC used must have interface pins.
The key of indirect substitution is to find out the basic electrical parameters, the internal equivalent PCB circuit, the function of each pin and the connection data between ic components. Attention should be paid in actual operation.
(1) Do not connect the pins of the integrated PCB by mistake.
(2) In order to adapt to the characteristics of the replaced IC, the components of the peripheral PCB circuit connected with it should be modified accordingly;
(3) the power supply voltage should be consistent with the replaced work. C. If the power supply voltage in the original PCB circuit is high, try to reduce the voltage; Low voltage, see if the alternative IC can work;
(4) After replacement, the static working current of ic should be measured. If the current is much larger than the normal value, it is clear that the PCB circuit may generate self-excitation, and then it must be decoupled and adjusted. If the gain is different from the original, the resistance of the feedback resistor can be adjusted;
(5) The input and output impedance of the IC after replacement should match the original PCB circuit; Check their driving ability;
(6) Make full use of pinholes and leads on the original PCB circuit board, and the external leads should be regular to avoid plugging and unplugging, so as to check and avoid self-excitation of PCB circuit, especially to avoid high-frequency self-excitation;
(7) It is best to connect a DC ammeter in series in the Vcc circuit of the power supply before powering on, and check whether the total current of the integrated PCB circuit changes normally from large to small.
6. Replace integrated circuit chips with discrete components.
Sometimes, the damaged part of the integrated circuit can be replaced by discrete components to restore its function. Before replacement, it is necessary to understand the internal functional principle of IC, the normal voltage and waveform diagram of each pin, and the working principle of PCB circuit with peripheral components. We should also consider:
Can the (1) signal be taken out of work C and connected to the input terminal of the peripheral PCB circuit?
(2) Whether the signal processed by the peripheral PCB circuit can be connected to the next level inside the integrated PCB circuit for reprocessing (the signal matching during connection should not affect its main parameters and functions). If the power amplifier IC is damaged, from the typical PCB circuit and internal PCB circuit, it is composed of audio amplifier, frequency discrimination and frequency amplification. The damaged part can be found by signal input method. If the audio amplification part is damaged, it can be replaced by discrete components.