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PCB Circuit Design in the IC Replacement Skills are Several?

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In the PCB circuit design will encounter the need to replace the IC chip time, the following is to say a few words in the replacement of IC chip in my skills, to assist designers in PCB circuit design can be more perfect.

A. Direct Substitution

Direct replacement refers to the use of other IC chips without any changes and directly replace the original IC, replacement does not affect the primary function of the machine and indicators.

The replacement guidelines are: replacement IC function, function indicators, packaging, pin usage, pin number and distance and other aspects are the same. The IC function of the same not only refers to the same function, should also pay attention to the same logic polarity, that is, the output input level polarity, voltage, current volts must be the same. Functional indicators refers to the primary electrical parameters of the IC (or the primary characteristic curve), most large power dissipation, most high operating voltage, frequency scale and the signal input, output impedance and other parameters with the original IC neighborhood. Small power substitutes to increase the heat sink.

a, The Same Type of IC Chip Replacement

The same type of IC chip replacement is generally reliable, the device integrated PCB circuit, pay attention to the direction not to be wrong, otherwise, the integrated PCB circuit is likely to be burned when the power is on. Some single-row plug-in amplifier IC, although the type, function, characteristics of the same, but the direction of the pin placement order is different. For example, dual-channel amplifier ICLA4507, pin "positive", "reverse" points, the beginning of the foot labeling (color dots or pits) in different directions: there is no suffix and the suffix for the "R ICs with no suffix and those with suffix "R", etc., e.g., M5115P and M5115RP.

b, Substitution of Different Types of ICs

 a) Substitution of ICs with the same type prefix letter and different numbers. This kind of replacement as long as the pin function between each other is exactly the same, its internal PCB circuit and electrical parameters are slightly different, can also be directly replaced with each other. Such as: accompanying sound amplifier IC LA1363 and LA1365, the latter than the former in the IC ⑤ foot internal increase of a voltage regulator diode, the other is identical.

 b) Type prefix letters are different, the same number of IC replacement. In general, the prefix letter is an indication of the manufacturer and the category of PCB circuit, the prefix letter followed by the same number, most of them can be directly replaced. But also a number, although the same number, but the function is completely different. For example, HA1364 is a companion IC, and uPC1364 is a color decoding IC; 4558, 8-pin operational amplifier NJM4558, 14-pin CD4558 digital PCB circuit; therefore, the two can not be replaced.

 c) The type of prefix letters and numbers are different IC replacement. Some manufacturers have introduced unencapsulated IC chip, and then processed into the factory named according to the product. There are also such as in order to improve certain parameters and indicators to improve the product. These products are commonly used in different types of naming or use the type of suffix to be different. For example, AN380 and uPC1380 can be directly replaced; AN5620, TEA5620, DG5620, etc. can be directly replaced.

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B. Non-direct Substitution

Non-direct substitution refers to the IC can not be directly replaced slightly amended peripheral PCB circuit, change the placement of the original pin or increase or decrease individual components, so that it can become a replacement IC method.

Replacement guidelines: replacement of the IC can be used with the original IC pin function is different, different shape, but the function should be the same, the characteristics of the neighborhood; replacement should not affect the function of the original machine.

a, The Same Class of Plastic But the Pin Function of Different IC Chip Replacement

This replacement needs to change the peripheral PCB circuit and pin placement, so it requires certain theoretical knowledge, complete information and rich practical experience and skills.

b, PCB Circuit Function is The Same But a Single Pin Function of Different lC Chip Replacement

Replacement can be based on the detailed parameters of each type of IC and clarification. Such as the AGC in the TV set, the video signal output has positive and negative polarity differences, as long as the output side of the inverter can be replaced. Hundred energy network belongs to the Qinji Group, is the domestic leading electronic industry service channel, online to provide components, sensors Acquisition, PCB customization, BOM single, material selection and other electronic industry supply chain solutions, one-stop to meet the comprehensive needs of small and medium-sized customers in the electronics industry.

c, Some Empty Pins Should not Be Privately Grounded

Internal equivalent PCB circuits and PCB circuits have some pins are not labeled, when encountering empty pins, should not be privately grounded, these pins for replacement or spare feet, and sometimes as an internal connection.

d, The Replacement of Different Packages of IC Chips

The same type of IC chip, but the package shape is different, the replacement of the new device as long as the pin according to the shape of the original device and the placement of the pin for shaping. For example, AFTPCB circuit CA3064 and CA3064E, the former for the round package, radial pins: the latter for the double in-line plastic package, the two internal characteristics are identical, according to the pin function can be connected. Dual-row ICAN7114, AN7115 and LA4100, LA4102 package is basically the same way, pins and heat sinks are exactly 180 degrees apart. Previously mentioned AN5620 with heatsink double in-line 16-pin package, TEA5620 double in-line 18-pin package, 9, 10 feet located on the right side of the integrated PCB circuit, equivalent to the AN5620 heatsink, the two other feet placed in the same way, will be 9, 10 feet connected to ground can be used.

e, Combination of Substitution

Combination of replacement is the same type of multiple IC internal PCB circuit is not damaged part, re-assembled into a good IC, to replace the poor function of the IC method. It is very suitable for the case where the original IC cannot be purchased. However, it is required that the PCB circuit inside the IC must have an interface pin.

The key to non-direct replacement is to find out the basic electrical parameters of the two ICs replaced each other, the internal equivalent PCB circuit, the function of the pins, the IC Department of the connection between the components of the information. Attention should be paid to the actual operation.

  a) Integrated PCB circuit pin numbering sequence, do not connect the wrong;

  b) In order to adapt to the characteristics of the replacement IC, connected to the peripheral PCB circuit components should be changed accordingly;

  c) The power supply voltage should be replaced with the work of the C in line with the original PCB circuit if the power supply voltage is high, we should try to reduce the voltage; low voltage, to see if the replacement IC can work;

  d) After the replacement to measure the IC's quiescent operating current, such as the current is much higher than normal, it is stated that the PCB circuit may produce self-excitation, which must be decoupled, adjusted. If the gain is different from the original, the feedback resistor can be adjusted;

  e) The input and output impedance of the replaced IC should be matched with the original PCB circuit; check its driving ability;

  f) In the alteration of the original PCB circuit board to fully use the foot holes and leads, external leads require regularity, to avoid front and back interspersed, in order to check and avoid PCB circuit self-excitation, especially to avoid high-frequency self-excitation;

  g) In the power supply before powering up the Vcc circuit most good and then connected in series to a current ammeter, step-down resistor resistance value from large to small to investigate the total current of the integrated PCB circuit to change whether it is normal.

f, Replace IC Chip With Discrete Components

Sometimes discrete components can be used to replace the damaged part of the IC to restore its function. Replacement should be understood before the internal function of the IC principle, the normal voltage of each pin, waveforms and peripheral components with the composition of the PCB circuit principle of operation. Together should also consider:

 (a) Whether the signal can be taken out of the work C connected to the input of the peripheral PCB circuit:

 (b) The signal processed by the peripheral PCB circuit, can be connected to the integrated PCB circuit within the next level to reprocessing (connecting the signal matching should not affect the primary parameters and functions). Such as in the amplifier IC damage, from the typical use of PCB circuit and internal PCB circuit, by the accompanying audio in the amplifier, frequency identification and frequency amplification level into, available signal input method to find out the damaged part, if the audio amplifier most of the damage, can be used as a substitute for discrete components.

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