08055A100FAT2A datasheet(39/46 Pages) AVX

39 / 46 page

tends to de-age capacitors and is why re-reading of capac-

itance after 12 or 24 hours is allowed in military specifica-

tions after dielectric strength tests have been performed.

Effects of Frequency – Frequency affects capacitance

and impedance characteristics of capacitors. This effect is

much more pronounced in high dielectric constant ceramic

formulation that is low K formulations. AVX’s SpiCap soft-

ware generates impedance, ESR, series inductance, series

resonant frequency and capacitance all as functions of fre-

quency, temperature and DC bias for standard chip sizes

and styles. It is available free from AVX.

Effects of Mechanical Stress – High “K” dielectric

ceramic capacitors exhibit some low level piezoelectric

reactions under mechanical stress. As a general statement,

the piezoelectric output is higher, the higher the dielectric

constant of the ceramic. It is desirable to investigate this

effect before using high “K” dielectrics as coupling capaci-

tors in extremely low level applications.

Reliability – Historically ceramic capacitors have been one

of the most reliable types of capacitors in use today.

The approximate formula for the reliability of a ceramic

capacitor is:

where

Lo = operating life

Tt = test temperature and

Lt = test life

To = operating temperature

Vt = test voltage

in °C

Vo = operating voltage

X,Y = see text

Historically for ceramic capacitors exponent X has been

considered as 3. The exponent Y for temperature effects

typically tends to run about 8.

A capacitor is a component which is capable of storing

electrical energy. It consists of two conductive plates (elec-

trodes) separated by insulating material which is called the

dielectric. A typical formula for determining capacitance is:

C =

.224 KA

C = capacitance (picofarads)

K = dielectric constant (Vacuum = 1)

A = area in square inches

t = separation between the plates in inches

(thickness of dielectric)

.224 = conversion constant

(.0884 for metric system in cm)

Capacitance – The standard unit of capacitance is the

farad. A capacitor has a capacitance of 1 farad when 1

coulomb charges it to 1 volt. One farad is a very large unit

and most capacitors have values in the micro (10-6), nano

(10-9) or pico (10-12) farad level.

Dielectric Constant – In the formula for capacitance given

above the dielectric constant of a vacuum is arbitrarily cho-

sen as the number 1. Dielectric constants of other materials

are then compared to the dielectric constant of a vacuum.

Dielectric Thickness – Capacitance is indirectly propor-

tional to the separation between electrodes. Lower voltage

requirements mean thinner dielectrics and greater capaci-

tance per volume.

Area – Capacitance is directly proportional to the area of

the electrodes. Since the other variables in the equation are

usually set by the performance desired, area is the easiest

parameter to modify to obtain a specific capacitance within

a material group.

100

1000 10,000 100,000

Hours

+1.5

-1.5

-3.0

-4.5

-6.0

-7.5

Characteristic

Max. Aging Rate %/Decade

C0G (NP0)

X7R

Z5U

Y5V

None

Figure 6

Typical Curve of Aging Rate

X7R Dielectric

General Description

08055A100FAT2A Datasheet(PDF) 39 Page - AVX Corporation

08055A100FAT2A Datasheet(HTML) 39 Page - AVX Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46

Datasheet Download

Link URL