The secret of derating - don't challenge Datasheet

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What is derating design ？ Why should we reduce the amount ？

The rating refers to the rated working condition , Derating is to ensure that the working conditions of our electronic circuit devices are within the rated range , Professionally speaking, the use stress of components is lower than the rated stress . If the derating is reduced more , Then the higher the requirements for components .

1. Why should we talk about derating design ？

There are two reasons , One reason is to improve system reliability , Improve the yield of production line , Reduce product failure rate ; Another reason is ： Save money . For example, the equipment needs the most 1A Current , But you chose to be able to bear 100A The inductance of , Can use is can use , But the money was wasted ？ This is over design . A separate 1 The cost of each piece of equipment is not much different , But for the equipment that shipped millions of units , The cost difference is not the slightest .

In addition to designing circuits, hardware engineers , Another important task is to make a trade-off between cost and performance , At the lowest possible cost , Achieve the best compromise between performance and stability , Is that you spend less money , The product performance is the same as that of the competitors , Even better , Be commonly called “ Inside the industry ”. therefore , When designing circuits 、 When selecting components , Be sure to carefully evaluate the parameters , Remember not to challenge at will datasheet or spec.

2. How do you do that ？

Like capacitors GRM32ER60E337ME05 The rated voltage is 2.5V, If derating 20%, That is according to （1-20%）*2.5=2V Environmental use ; If derating 30%, That is according to （1-30%）*2.5=1.75V Environmental use , Leave a little margin for the rated operating voltage .

Some engineers raised objections , For example, the capacitor mentioned above , Some people would say ,“ Although the rated operating voltage indicated in the capacitance manual is 2.5V, But they have been following 3V Normal use , Then don't worry about derating , Don't tube datasheet 了 , In the future, follow 3V use .”

This is a loose R & D attitude , The risk is very high , We often say internally “ Keep in awe of technology ”, Although we need to test the performance parameters of the capacitor 、 Small batch trial production verification 、 Mass market validation , But even the over validation is normal , We shouldn't go beyond datasheet Use .

This is because , Component manufacturers only pay attention to their datasheet be responsible for , They believe that devices can only be used under manual conditions , It's safe and reliable , Performance and reliability cannot be guaranteed beyond the conditions in the manual , They will not be responsible for it .

3. Why do some people overuse it without exposing problems ？

Yes 3 One reason , The first reason is , Device manufacturers will leave some margin for themselves , Although it is written that 2.5V, But the reality may be 3.0V, Save some for yourself buffer.

The second reason is the probability event , The model of performance parameters is close to normal distribution , The performance parameters of most capacitors are very good , Only a few capacitance performance parameters are not enough , There may be a small number of capacitors rated above 3.0V, It is not exposed during small batch production .

The third reason is , The manufacturing process of the manufacturer affects , For example, a certain type of components , The old production line has been used for a long time , Backward technology ,MOS And so on , The withstand voltage value is high . Later, in order to improve production efficiency , lower production cost , Carry out production line integration , Replace it with a new production line , The new production line has advanced technology , The pipes are thin , Low withstand voltage , But still datasheet Within the requirements . For example, the voltage value of the capacitor starts from the beginning 3.0V Down to 2.6V, I still did datasheet Medium 2.5V, If the hardware engineer still exceeds the previous experience datasheet Of 3.0V Use , Then there is likely to be a large area of defects .

therefore , Hardware engineers must learn to reduce the amount scientifically and reasonably , Learn to save money scientifically and reasonably .

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