SOLID TANTALUM CHIP CAPACITORS
TANTALUM MnO
2
COMPONENT PERFORMANCE CHARACTERISTICS
(con’t.)
ESR — Represents the actual ohmic series resis-
tance in series with the capacitance. Lead wires
and capacitor electrodes are contributing sources.
R
L
— Capacitor Leakage Resistance. Typically it
can reach 50,000 megohms in a tantalum capaci-
tor. It can exceed 10
12
ohms in monolithic ceram-
ics and in film capacitors.
R
d
— The dielectric loss contributed by dielectric
absorption and molecular polarization. It becomes
very significant in high frequency measurements
and applications. Its value varies with frequency.
C
d
— The inherent dielectric absorption of the
solid tantalum capacitor which typically equates to
1-2% of the applied voltage.
As frequency increases, X
C
continues to decrease
according to its equation above. There is unavoid-
able inductance as well as resistance in all capaci-
tors, and at some point in frequency, the reac-
tance ceases to be capacitive and becomes
inductive. This frequency is called the self-reso-
nant point. In solid tantalum capacitors, the reso-
nance is damped by the ESR, and a smooth,
rather than abrupt, transition from capacitive to
inductive reactance follows.
Typical ESR/Z frequency response curves are
shown in Figures 9a and 9b. These curves are
for selected ratings and represent typical T491
Series performance. Maximum limits for 100 kHz
ESR are listed in the part number tables for
each series. Note that the T494 Series offers low
ESR and the T495 Series is specially designed
for very low ESR performance. Refer to page 31
for more information. See also KEMET’s T510
Series low ESR ratings on page 40.
X
C
= 1 ohm
2 fC
where:
f = frequency, Hertz
C = capacitance, Farad
FIGURE 7a
Total Impedance of the Capacitor Below
Resonance
X
L
= 2 fL
where:
f = frequency, Hertz
L = inductance, Henries
FIGURE 7b Total Impedance of the Capacitor Above
Resonance
To understand the many elements of a capaci-
tor, see Figure 8.
ESL
ESR
C
R
L
C
d
FIGURE 8
The Real Capacitor
R
d
8
A capacitor is a complex impedance consisting of
many series and parallel elements, each adding
to the complexity of the measurement system.
ESL — Represents lead wire and construction
inductance. In most instances (especially in solid
FIGURE 9a ESR & Impedance (Z) vs Frequency
tantalum and monolithic ceramic capacitors) it is
insignificant at the basic measurement frequen-
cies of 120 and 1000 Hz.
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