|Description||MULTILAYER CERAMIC CAPACITORS/AXIAL & RADIAL LEADED|
|C052/56G Datasheet PDF : 14 Pages |
APPLICATION NOTES FOR MULTILAYER
The fundamental electrical properties of multilayer
ceramic capacitors are as follows:
Polarity: Multilayer ceramic capacitors are not polar,
and may be used with DC voltage applied in either direction.
Rated Voltage: This term refers to the maximum con-
tinuous DC working voltage permissible across the entire
operating temperature range. Multilayer ceramic capacitors
are not extremely sensitive to voltage, and brief applications
of voltage above rated will not result in immediate failure.
However, reliability will be reduced by exposure to sustained
voltages above rated.
Capacitance: The standard unit of capacitance is the
farad. For practical capacitors, it is usually expressed in
microfarads (10-6 farad), nanofarads (10-9 farad), or picofarads
(10-12 farad). Standard measurement conditions are as
Class I (up to 1,000 pF):
Class I (over 1,000 pF):
1MHz and 1.2 VRMS
1kHz and 1.2 VRMS
1 kHz and 1.0 ± 0.2 VRMS.
1 kHz and 0.5 ± 0.1 VRMS.
The variation of a capacitor’s impedance with frequency
determines its effectiveness in many applications.
Dissipation Factor: Dissipation Factor (DF) is a mea-
sure of the losses in a capacitor under AC application. It is the
ratio of the equivalent series resistance to the capacitive reac-
tance, and is usually expressed in percent. It is usually mea-
sured simultaneously with capacitance, and under the same
conditions. The vector diagram in Figure 2 illustrates the rela-
tionship between DF, ESR, and impedance. The reciprocal of
the dissipation factor is called the “Q”, or quality factor. For
convenience, the “Q” factor is often used for very low values
of dissipation factor. DF is sometimes called the “loss tangent”
or “tangent ␦”, as derived from this diagram.
Like all other practical capacitors, multilayer ceramic
capacitors also have resistance and inductance. A simplified
schematic for the equivalent circuit is shown in Figure 1.
Other significant electrical characteristics resulting from
these additional properties are as follows:
C = Capacitance
L = Inductance
R = Equivalent Series Resistance (ESR)
R = Insulation Resistance (IR)
Impedance: Since the parallel resistance (Rp) is nor-
mally very high, the total impedance of the capacitor is:
RS2+ (XC - XL)2
Where Z = Total Impedance
RS = Equivalent Series Resistance
XC = Capacitive Reactance
XL = Inductive Reactance = 2πfL
Insulation Resistance: Insulation Resistance (IR) is the
DC resistance measured across the terminals of a capacitor,
represented by the parallel resistance (Rp) shown in Figure 1.
For a given dielectric type, electrode area increases with
capacitance, resulting in a decrease in the insulation resis-
tance. Consequently, insulation resistance is usually specified
as the “RC” (IR x C) product, in terms of ohm-farads or
megohm-microfarads. The insulation resistance for a specific
capacitance value is determined by dividing this product by
the capacitance. However, as the nominal capacitance values
become small, the insulation resistance calculated from the
RC product reaches values which are impractical.
Consequently, IR specifications usually include both a mini-
mum RC product and a maximum limit on the IR calculated
from that value. For example, a typical IR specification might
read “1,000 megohm-microfarads or 100 gigohms, whichever
Insulation Resistance is the measure of a capacitor to
resist the flow of DC leakage current. It is sometimes referred
to as “leakage resistance.” The DC leakage current may be
calculated by dividing the applied voltage by the insulation
resistance (Ohm’s Law).
Dielectric Withstanding Voltage: Dielectric withstand-
ing voltage (DWV) is the peak voltage which a capacitor is
designed to withstand for short periods of time without dam-
age. All KEMET multilayer ceramic capacitors will withstand a
test voltage of 2.5 x the rated voltage for 60 seconds.
KEMET specification limits for these characteristics at
standard measurement conditions are shown in Table 1 on
page 4. Variations in these properties caused by changing
conditions of temperature, voltage, frequency, and time are
covered in the following sections.
© KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606, (864) 963-6300
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Multilayer ceramic capacitors are available in a variety of physical sizes and configurations, including leaded devices and surface mounted chips. Leaded styles include molded and conformally coated parts with axial and radial leads. However, the basic capacitor element is similar for all styles. It is called a chip and consists of formulated dielectric materials which have been cast into thin layers, interspersed with metal electrodes alternately exposed on opposite edges of the laminated structure. The entire structure is fired at high temperature to produce a monolithic block which provides high capacitance values in a small physical volume. After firing, conductive terminations are applied to opposite ends of the chip to make contact with the exposed electrodes. Termination materials and methods vary depending on the intended use.
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