One, direct substitution
Direct substitution refers to directly replacing the original IC with other IC chips without any changes, and the main functions and indicators of the machine will not be affected after the substitution.
The replacement criterion is: the function, function index, packaging method, pin usage, pin number and distance of the replacement IC are the same. In the meantime, the same function of the IC not only means the same function, but also the same logic polarity, that is, the output and input level polarity, voltage, and current fluctuations must be the same. The functional index refers to the IC's primary electrical parameters (or primary characteristic curve), maximum power dissipation, maximum operating voltage, frequency scale, and various signal input and output impedance parameters to be close to the original IC. Substitutes with low power should increase the heat sink.
1. Replacement of the same type of IC chip
The replacement of the same type of IC chip is generally reliable. When installing the integrated PCB circuit, pay attention to the direction and not get it wrong, otherwise, the integrated PCB circuit may be burned when the power is turned on. Some single in-line power amplifier ICs have the same type, function, and characteristics, but the direction of the pin placement order is different. For example, the dual-channel power amplifier ICLA4507 has "positive" and "negative" pins, and the initial pin markings (color dots or pits) are in different directions: there is no suffix and the suffix is "R", IC, etc., for example M5115P and M5115RP.
2. Substitution of different types of IC
(1) Substitution of IC with the same type prefix letter and different numbers. As long as the functions of the pins are exactly the same, the internal PCB circuit and electrical parameters of this substitution are slightly different, and they can also be directly substituted for each other. For example: the sound amplifier IC LA1363 and LA1365, the latter adds a Zener diode inside IC pin ⑤ compared with the former, and the others are exactly the same.
(2) Substitution of IC with different type prefix letters and the same number. In general, the prefix letter indicates the manufacturer and the category of the PCB circuit. The numbers after the prefix letter are the same, and most of them can be directly replaced. But also count, although the number is the same, but the function is completely different. For example, HA1364 is a sound IC, while uPC1364 is a color decoding IC; 4558, 8-pin is an operational amplifier NJM4558, 14-pin is a CD4558 digital PCB circuit; so the two cannot be replaced at all.
(3) Type prefix letters and numbers are different from IC substitution. Some manufacturers import unpackaged IC chips and then process them into products named after the factory. Another example is to improve the product in order to improve certain parameters. These products are often named by different types or differentiated by type suffixes. For example, AN380 and uPC1380 can be directly replaced; AN5620, TEA5620, DG5620, etc. can be directly replaced.
2. Indirect substitution
Indirect replacement refers to the method of making IC that cannot be directly replaced by slightly modifying the peripheral PCB circuit, changing the original pin placement or adding or removing individual components, etc., to make it a replaceable IC.
Substitution criteria: The IC used for the replacement can have different functions and different appearances from the original IC, but the functions should be the same and the characteristics should be nearby; the function of the original machine should not be affected after the replacement.
1. Substitution of IC chips with the same type of plastic but different pin functions
This kind of substitution requires changes to the peripheral PCB circuit and pin placement, so it requires certain theoretical knowledge, good information, and rich practical experience and skills.
2, PCB circuit function is the same, but the single pin function is different, the replacement of IC chip
The replacement can be carried out according to the detailed parameters and clarifications of each type of IC. For example, there is a difference between the positive and negative polarity of the AGC and video signal output in the TV, as long as the inverter is connected to the output terminal, it can be replaced. Baineng.com is a subsidiary of Qinji Group and is the leading electronic industry service channel in China. It provides online components, sensor acquisition, PCB customization, BOM distribution, material selection and other electronic industry supply chain complete solutions, one-stop satisfactory electronics Comprehensive needs of small and medium-sized industrial customers.
3. Some empty feet should not be grounded privately
The internal equivalent PCB circuit and the use of the PCB circuit have some lead-out pins that are not marked. When there are empty lead-out pins, they should not be grounded privately. These lead-out pins are alternate or spare pins, and sometimes they are also used as internal connections.
4. Replacement of IC chips with different packages
The same type of IC chip, but the package shape is different, only need to reshape the pins of the new device according to the shape and placement of the original device pins. For example, the AFTPCB circuit CA3064 and CA3064E, the former is a circular package with radial pins: the latter is a dual-in-line plastic package, the internal characteristics of the two are exactly the same, and they can be connected according to the pin function. Dual-row ICAN7114, AN7115 and LA4100, LA4102 are basically the same in packaging, and the pins and heat sink are exactly 180 degrees apart. The aforementioned AN5620 dual in-line 16-pin package with heat sink and TEA5620 dual in-line 18-pin package. Pins 9 and 10 are located on the right side of the integrated PCB circuit, which is equivalent to the heat sink of AN5620. The other pins of the two are placed in the same way. , Connect 9 and 10 feet to ground to use.
5. Combination substitution
Combination substitution is a method of recombining the undamaged PCB circuit parts of multiple ICs of the same type into a good IC to replace the poorly functioning IC. It is very applicable when the original IC is not available. However, it is required that a good PCB circuit inside the IC used must have an interface pin.
The key to non-direct substitution is to find out the basic electrical parameters, internal equivalent PCB circuit, the function of each pin, and the connection and connection data between the components of the IC part of the two ICs that are substituted for each other. Be careful in actual operation.
(1) The number sequence of the integrated PCB circuit pins, do not connect them wrong;
(2) In order to adapt to the characteristics of the replaced IC, the components of the peripheral PCB circuit connected to it should be modified accordingly;
(3) The power supply voltage should be consistent with the replaced IC. If the power supply voltage in the original PCB circuit is high, try to reduce the voltage; if the voltage is low, it depends on whether the replacement IC can work;
(4) After the replacement, the quiescent operating current of the IC should be measured. If the current is much larger than the normal value, it means that the PCB circuit may be self-excited. At this time, decoupling and adjustment must be carried out. If the gain is different from the original, the resistance of the feedback resistor can be adjusted;
(5) After the replacement, the input and output impedance of the IC must match the original PCB circuit; check its drive capability;
(6) Make full use of the pin holes and leads on the original PCB circuit board when making changes. The external leads are required to be regular and avoid interspersing before and after, so as to check and avoid PCB circuit self-excitation, especially to avoid high-frequency self-excitation;
(7) It is better to connect a current meter in series in the Vcc loop of the power supply before power-on, and investigate whether the change of the total current of the integrated PCB circuit is normal.
6. Replace IC chips with discrete components
Sometimes, discrete components can be used to replace the damaged part of the IC to restore its function. Before replacement, you should understand the internal function principle of the IC, the normal voltage of each pin, the waveform diagram, and the operating principle of the PCB circuit with peripheral components. Together, you should also consider:
(1) Whether the signal can be taken out from 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 stage inside the integrated PCB circuit for reprocessing (the signal matching during connection should not affect its primary parameters and functions). If the intermediate amplifier IC is damaged, from the typical use of the PCB circuit and the internal PCB circuit, it is composed of audio intermediate amplifier, frequency discrimination and frequency boosting. The signal input method can be used to find the damaged part. If the audio amplifier part is damaged, discrete components can be used. Device replacement.
The above is how many IC substitution techniques in PCB circuit design are there? An introduction to the two techniques of IC substitution, I hope it can help everyone and want to learn more about PCB circuit design information, please follow us.