Author Topic: What is X7R and X5R of ceramic capacitor?  (Read 28430 times)

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Offline javad2040Topic starter

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What is X7R and X5R of ceramic capacitor?
« on: August 17, 2017, 09:08:40 am »
hi.
I design a pcb for Xilinx Spartan 6 FPGA and i used lm1064 for produce 3.3v for FPGA. for getting this voltage i need to use 100nf ceramic capacitor in input.
by searching in the capacitor schematic, i found X7R and X5R features of capacitor. what is X7R and X5R and why they are important?
 

Offline nugglix

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #1 on: August 17, 2017, 09:18:37 am »
See:


 

Offline Rerouter

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #2 on: August 17, 2017, 09:41:41 am »
X7R and X5R are dielectrics of ceramic capacitors, these dielectrics describe the limit of tolerances over temperature span,

In both cases to see if suitable requires looking at the datasheet, as there are other parameters like voltage de-rating, e.g. the effective capacitance value is lower when the supply voltage is higher. this changes even between voltage ratings of the same series of caps, and sometimes a 5V cap is better than a 25V, as the higher voltage in the same package meant the derating curve was sacrificed to meet the spec.
 

Online Benta

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #3 on: August 17, 2017, 12:13:29 pm »
X7R and X5R are the lowest grade of ceramic caps, but with the highest capacitance/volume ratio. If these grades are specified, it basically means you use almost anything. They are mostly used for supply decoupling purposes.
 

Offline chris_leyson

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #4 on: August 17, 2017, 01:16:34 pm »
X7R are rated to 125C whereas X5R is only rated to 85C. The R suffix tells you that the capacitance change over temperature is +/- 15%. There is also a capacitance change with applied DC voltage, capacitance drops with an increase in applied DC voltage and X7R performs slightly better than X5R. Dielectrics to be avoided are things like Y5V as the capacitance will drop to only 15% or 20% of the rated value at max rated temp of 85C. Capacitance drop with increased apllied voltage is very dependant on package size with larger packages performing much better than the smaller 0603 or 0805 packages. There's a good app note from Maxim explaining some of the issues,
https://www.maximintegrated.com/en/app-notes/index.mvp/id/5527 as well as some good app notes from Murata and TDK. If capacitance change with temperature or applied voltage is an important part of the design then read the manufacturers data sheet.
 

Offline djnz

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #5 on: August 18, 2017, 11:28:47 am »
The Wikipedia article on 'Ceramic Capacitor' is quite informative.



   



   


« Last Edit: August 18, 2017, 11:32:09 am by djnz »
 

Offline w2aew

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #6 on: August 18, 2017, 05:21:10 pm »
X7R and X5R are the lowest grade of ceramic caps, but with the highest capacitance/volume ratio. If these grades are specified, it basically means you use almost anything. They are mostly used for supply decoupling purposes.

Not really - the X7R really aren't too bad, X5R are a little worse (lower high temp limit). Each of these is a Class 2 dielectric, not as good as Class 1. The "lowest grade" ceramic caps are most commonly the Y5V and Z5U types.  See the tables (above) for the 'decoder' for these ceramic types.
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Offline metrologist

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Re: What is X7R and X5R of ceramic capacitor?
« Reply #7 on: August 18, 2017, 05:50:37 pm »
that second video's title frame, capacitor far left. I have a couple drawer of those...
 


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