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IC substitution techniques in PCB circuit design


When you need to replace ICs in PCB circuit design, here are the tips to replace ICs to help designers be more perfect in PCB circuit design.

Direct substitution

Direct replacement refers to directly replacing the original IC with other ICs without any changes. The replacement will not affect the main performance and indicators of the machine.
Its replacement principle is: the functions, performance indicators, package form, pin usage, pin serial number, and interval of the replacement IC are the same. The same function of the IC means not only the same function, but also the same logic polarity, that is, the polarity of the input and output levels, voltage, and current amplitude must be the same. The performance index means that the main electrical parameters (or main characteristic curves), maximum power dissipation, maximum operating voltage, frequency range, and various signal input and output impedance of the IC should be similar to the original IC. For low-power substitutes, increase the heat sink.

1. Replacement of the same type of IC

The replacement of the same type of IC is generally reliable. When installing the integrated PCB circuit, care must be taken to ensure that the direction is not wrong. Otherwise, the integrated PCB circuit is likely to be burned when powered on. Some single in-line power amplifier ICs have the same model, function, and characteristics, but the direction of the pinout order is different.

2.Substitution of ICs with the same model prefix letters and different numbers

As long as the pin functions are the same, the internal PCB circuit and electrical parameters are slightly different, and they can also be directly replaced with each other.

In general, the prefix letter indicates the type of manufacturer and PCB circuit. The numbers after the prefix letter are the same, and most of them can be replaced directly. But there are a few special cases. Although the numbers are the same, the functions are completely different.


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Second, indirect substitution

Non-direct replacement refers to a method in which an IC that cannot be directly replaced slightly modifies the peripheral PCB circuit, changes the arrangement of the original pins, or adds or removes individual components to make it a replaceable IC.
Substitution principle: The IC used for substitution can have different functions and different shapes from the original IC pins, but the functions must be the same and the characteristics should be similar; the performance of the original machine should not be affected after substitution.

1.Replacement of different packaged ICs

The same type of IC chip, but the package shape is different. When replacing, just reshape the pins of the new device according to the shape and arrangement of the pins of the original device.

2.PCB circuit function is the same but individual pin function is different

The replacement can be carried out according to the specific parameters and instructions of each type of IC. For example, there is a difference between positive and negative polarity of AGC and video signal output in the TV, as long as an inverter is connected to the output end, it can be replaced.


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3.Replacement of ICs with the same plastic type but different pin functions

This replacement requires changing the peripheral PCB circuit and pin arrangement, and therefore requires certain theoretical knowledge, complete information, and rich practical experience and skills.

4.some empty feet should not be grounded without authorization

Some pinouts in the internal equivalent PCB circuit and application PCB circuit are not marked. When encountering empty pinouts, you should not arbitrarily ground them. These pinouts are replacement or spare pins, and sometimes also used as internal connections.

5.combination substitution

The combination replacement is a method of recombining the undamaged PCB circuit parts of multiple ICs of the same model into a complete IC to replace a poorly functioning IC. It is very applicable when the original IC cannot be purchased. However, the intact PCB circuit used in the IC must have an interface pin.


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6.Replace IC with discrete components

Sometimes damaged components in an IC can be replaced with discrete components to restore functionality. Before replacement, you should understand the internal function principle of the IC, the normal voltage of each lead pin, the waveform diagram, and the working principle of the PCB circuit with peripheral components. You should also consider:

(1) Can the signal be taken out from the industrial 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 main parameters and performance). If the intermediate amplifier IC is damaged, from the typical application PCB circuit and internal PCB circuit, it is composed of audio amplifier, frequency discriminator, and frequency amplification. The signal input method can be used to find the damaged part. If the audio amplifier part is damaged, discrete components can be used instead.


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