Direct substitution refers to the use of other IC without any changes and directly replace the original IC, after the substitution does not affect the machine's main performance and indicators.
The substitution principle is: the function, performance index, package form, pin use, PIN number and interval of the substitution IC are the same. The function of IC not only means the same function, but also the same logic polarity, that is, the output input level polarity, voltage, current amplitude must be the same. For example: The image of IC, TA7607 and TA7611, the former is the reverse of the high-level AGC, the latter is a positive and high-level AGC, it can not be directly substituted. In addition to the output of different polar aft voltage, the output of different polarity of synchronous pulses such as IC can not be directly substituted, even with 1270 _f8 companies or manufacturers of products, should pay attention to the distinction. The performance index refers to the IC's main electrical parameters (or the main characteristic curve), the maximum dissipation power, the maximum operating voltage, the frequency range and the signal input, the output impedance and other parameters to be similar to the original IC. Small power of the substitute to increase the heat sink. 
1. Substitution of the same type IC
The replacement of the same type of IC is generally reliable, the installation of integrated circuits, should pay attention to the direction of not mistaken, otherwise, the power when the integrated circuit is likely to be burned. Some single row direct plug type power amplifier IC, although the model, the function, the characteristic is same, but the pin arranges the order the direction is different. For example, dual channel power amplifier IC LA4507, its pin has "positive", "inverse" of the points, its starting pin mark (color point or concave hole) direction is different, no suffix and suffix "R" ic, such as m5115p and M5115RP.
2. Substitution of different types of IC
⑴ model prefix letter, the number of different IC substitution. This substitution as long as the PIN function is identical, the internal circuit and electrical parameters are slightly different, but also can be directly substituted for each other. such as: Sound in the IC LA1363 and LA1365, the latter than the former in the IC ⑤ foot added a Zener diode, the other exactly the same.
⑵ model prefix letters are different, the number of the same IC substitution. In general, the prefix letter is the type of manufacturer and circuit, followed by the same number of prefixes, most of which can be directly substituted. But there are also a few, although the number is the same, but the function is completely different. For example, HA1364 is a sound IC, and uPC1364 is a color decoder IC, 4558, 8 feet is the operational amplifier NJM4558, 14 feet is the CD4558 digital circuit;
⑶ model prefix letters and numbers are different IC substitutions. Some manufacturers to introduce an unpackaged IC chip, and then processed into a product named after the factory. It is also like improving the product to improve some parameter index. These products are commonly used to name different models or to differentiate them by designation suffixes. For example, AN380 and uPC1380 can be substituted directly, and AN5620, TEA5620 and DG5620 can be substituted directly.