ELECTRICAL CHARACTERISTICS
The fundamental electrical properties of multilayer
c
eramic capacitors are as follows:
Polarity: Multilayer ceramic capacitors are not polar,
a
nd 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
o
f 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
follows:
Class I (up to 1,000 pF): 1MHz and 1.2 VRMS
maximum.
Class I (over 1,000 pF): 1kHz and 1.2 VRMS
maximum.
Class II: 1 kHz and 1.0 ± 0.2 VRMS.
Class III: 1 kHz and 0.5 ± 0.1 VRMS.
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:
Impedance: Since the parallel resistance (Rp) is nor-
mally very high, the total impedance of the capacitor is:
Figure 1
C = Capacitance
L = Inductance
R
S
= Equivalent Series Resistance (ESR)
R
P
= Insulation Resistance (IR)
R
P
R
S
C
L
Z =
Where Z = Total Impedance
RS = Equivalent Series Resistance
X
C
= Capacitive Reactance =
2ππfC
X
L
= Inductive Reactance = 2ππfL
1
R
S
+ (X
C
- X
L
)
22
DF =
ESR
X
c
X
c
2πfC
1
=
Figure 2
δ
Ζ
O
X
c
ESR
The variation of a capacitor’s impedance with frequency
determines its effectiveness in many applications.
Dissipation Factor: Dissipation Factor (DF) is a mea-
s
ure of the losses in a capacitor under AC application. It is the
ratio of the equivalent series resistance to the capacitive reac-
t
ance
,
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
t
he 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
d”, as derived from this diagram.
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
is less.”
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 5
APPLICATION NOTES FOR MULTILAYER
CERAMIC CAPACITORS
Application Notes
