PCB Circuit Design IC substitution tips

- Aug 10, 2016-

In the PCB circuit design experience required IC substitution when, following to share with you at 

the time of the substitution IC tips to help designers in the PCB circuit design can be more 

perfect.

A direct substitution

Direct substitution refers to other IC without any changes directly replace the original IC, after

the substitution does not affect the performance of the main indicators of the machine.

It is the principle of substitution: substitution of several IC functionality, performance, package,

pin usage, pin number and spacing, etc. are the same. Which refers not only to the IC functions the 

same same function, the logic is also noted that the same polarity, i.e., the output polarity of 

the input level, voltage, current amplitude must be the same. Performance refers to the main 

electrical parameters (or principal characteristic curve) IC, the maximum power dissipation, the 

maximum operating voltage, frequency range and each signal input and output impedance and other 

parameters are similar to the original IC. Replacement power small pieces to increase the heat sink.

1, the same type IC substitution

The same type IC substitution is generally reliable, the installation of an integrated circuit PCB,

pay attention to the direction of no mistake, otherwise, the integrated PCB circuit while power is 

likely to be burned. Some single in-line amplifier IC, although the type and function, the same 

characteristics, but the direction of the pin order is different. For example, two-channel amplifier

ICLA4507, pins have "positive", "R" points, its different starting foot dimension (colored dots or 

pits) direction: no suffix and suffix "R", the IC, for example, M5115P and M5115RP.

2, the same model prefix letters, numbers substitution of different IC

As long as this substitution pin functions are identical to each other, and its internal circuitry 

and PCB slightly different electrical parameters, but also with each other directly substitution. 

Such as: the sound and put ICLA1363 LA1365, the latter is within 5 feet IC adds a Zener diode, the 

other exactly the same.

Under normal circumstances, the prefix letter indicates the category of manufacturers and PCB 

circuit, the same prefix letters behind the numbers, most of which can direct substitution. But also

a small number of exceptions, although the same number, but the functionality is completely 

different. For example, HA1364 is sound IC, and is uPC1364 color decoding IC; number is 4558, the 

operational amplifier 8 feet NJM4558,14 feet are CD4558 digital PCB circuit; so the two can not be 

totally substitution. So be sure depends pin functions.

Some manufacturers to introduce unpackaged IC chip, and then processed into products named by the 

factory, there are certain parameters in order to improve the indicators and improved products. 

These products are commonly used in different models or named by the designation suffix to 

distinguish. For example, AN380 and uPC1380 direct substitution, AN5620, TEA5620, DG5620 and other 

direct substitution.

Second, the indirect substitution

Non-direct substitution refers to the substitution of the IC can not be directly slightly modified 

peripheral PCB circuit, change the arrangement of the original pin or changes in individual 

components, so that it may become the method of IC substitution.

The principle of substitution: substitution of the IC can be used with the original IC pin functions

in different, different shapes, but the functions must be the same, similar to characteristics; 

after substitution should not affect the performance of the original machine.

1, different package IC substitution

The same type of IC chip, but the package outline different, as long as the original shape and pin 

arrangement of new devices for shaping device pins when substitution. For example, AFTPCB circuit 

CA3064 and CA3064E, former circular package, radial pin: the latter is dual in-line plastic package,

the internal characteristics of both exactly the same, according to the pin function to connect to. 

Double row ICAN7114, AN7115 and LA4100, LA4102 package is basically the same, pins and fins are 

just 180 degrees. AN5620 aforementioned heatsink DIP 16-pin package, TEA5620 18-pin dual in-line 

package, located on the right foot 9,10 integrated PCB circuit, the equivalent of AN5620 heat sink,

the other two legs are arranged as 9,10 feet will link the ground can be used.

2, PCB circuit function the same, but different functions of individual pins lC substitution

It can be carried out according to various models of IC specifications and instructions when 

substitution. Such as a television in the AGC, the output video signal has positive and negative 

difference, as long as the substitution can be affixed at the output of the inverter later.

3, the same type of plastic pin functions but different IC substitution of

This substitution need to change the peripheral circuit and PCB pin arrangement, which requires a 

certain theoretical knowledge, complete information and a wealth of practical experience and skills.

4, some empty foot ground should not be allowed

Internal equivalent circuit PCB and PCB circuit in some application leads to the foot is not marked,

encounter leads to foot, the ground should not be allowed to empty, these pin-outs for the 

replacement or alternate feet, sometimes as an internal connection.

5. The composition substitution

Substitution is a combination of the plurality of IC inside the same model intact PCB circuit, 

re-assembled into a complete IC, IC method used instead dysfunctional. The next buy wife IC 

situation is very suitable. But requires the use of IC internal circuit must be intact PCB 

interface leads to foot.

Non-direct substitution key is to find out the basic electrical parameters mutually substitution 

two IC, the internal equivalent circuit between the PCB, the pin functions, IC unit element 

connected data relationships. The actual operation should pay attention to the following points:

(1) integrated circuit PCB pin number order, do not take the wrong;

(2) In order to meet the characteristics of IC substitution after peripheral elements connected 

thereto PCB circuit to be changed accordingly;

(3) the power supply voltage to be consistent with the substitution of work after C, if the 

original PCB circuit power supply voltage is high, should try to buck; voltage is low, IC 

substitution depends on whether the work;

(4) After the substitution IC quiescent current to be measured, such as the current is much larger 

than normal, then the PCB may occur from shock, then it must be decoupled adjustment. If the gain 

vary with the original, you can adjust the feedback resistor;

(5) After the substitution IC input and output impedance of the circuit to be matched with the 

original PCB; check drive capability;

(6) When the changes to take full advantage and a lead foot holes, external leads original PCB 

board requirements, avoided around the cross, in order to check and prevent the PCB from shock, 

particularly to prevent high-frequency self-excited;

(7) with the power supply Vcc circuit before the best in the series has been re-flow meter, 

descending down resistor to see if the total current change integrated PCB circuit normal.

6, IC substitution with discrete components

IC substitution can sometimes be discrete components being damaged part, to restore function. You 

should know before substitution principle internal functions of the IC, the normal voltage of each 

pin out waveform and peripheral components and working principle of the PCB. We should also 

consider:

(1) remove the signal can be connected to the peripheral circuit PCB input from workers in the C:

(2) by the peripheral circuit after the signal processing PCB, PCB can connect to the integrated 

circuit inside the next level to be re-treated (match signal connection should not affect the main 

parameters and performance). As put IC damage from typical application circuit PCB and PCB 

internal circuit, the sound amplified by the frequency discriminator and amplifier stage Jin Cheng,

usable signal input to identify damaged parts, if partially damaged audio amplifier, you can use 

discrete components instead.


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