KEMET®
APPLICATION NOTES FOR TANTALUM CAPACITORS
monolithic ceramic capacitors) it is insignificant at the
basic measurement frequencies of 120 and 1000 Hz.
RS — Represents the actual ohmic series resistance
in series with the capacitance. Lead wires and capacitor
electrodes are contributing sources.
RL — Capacitor Leakage Resistance. Typically it can
reach 50,000 megohms in a tantalum capacitor. It can
exceed 1012 ohms in monolithic ceramics and in film
capacitors.
Rd — The dielectric loss contributed by dielectric
absorption and molecular polarization. It becomes very
significant in high frequency measurements and applica-
tions. Its value varies with frequency.
35VDC Rated
Impedance
ESR
(Ohms)
100
10
1
4
.
7
µ
F
d
2
2
µ
F
d
4.7
µ
Fd
47
µFd
0.1
2
2
µ
F
d
Cd — The inherent dielectric absorption of the solid
tantalum capacitor which typically equates to 1-2% of the
applied voltage.
100
1000
10K
100K
1M
10M
Frequency (MHz)
Figure 11a. ESR and Impedance vs. Frequency
As frequency increases, Xc continues to decrease
according to its equation above. There is unavoidable
inductance as well as resistance in all capacitors, and at
some point in frequency, the reactance ceases to be
capacitive and becomes inductive. This frequency is called
the self-resonant point. In solid tantalum capacitors, the
resonance is damped by the ESR, and a smooth, rather
than abrupt, transition from capacitive to inductive reac-
tance (XL = 2pfL) follows.
Typical ESR and Z performance is given for repre-
sentative capacitor ratings in Figures 9 through 11.
Measured impedance will be affected by the length of lead
wire included. Data for the curves were taken by including
1/2" of each lead wire in the measuring circuit.
Despite the fact that the reactance is entirely induc-
tive above the self-resonance, these capacitors find use
as decoupling devices above 10 MHz. Special designs
have been developed for minimum inductance and are
used above 100 MHz.
10VDC Rated
ESR and Z are also affected by temperature. At 100
kHz, ESR decreases with increasing temperature. The
amount of change is influenced by the size of the capaci-
tor and is generally more pronounced on smaller ratings.
Impedance
100
ESR
(Ohms)
10
Multiplier of 100kHz ESR
10
10
µ
Fd
1
1
0
0
µ
F
d
0.1
100
1
1000
10K
100K
1M
10M
Frequency (MHz)
0.1
ESR and Impedance vs. Frequency
20VDC Rated
Figure 9.
-50
-25
0
25
50
75
100
125
Temperature - Degrees Centigrade
Figure 11b Typical Effect of Temperature
on 100 kHz ESR
30
10
3
Impedance
ESR
(Ohms)
13. POWER DISSIPATION
Permissible power dissipation has been empirically
established for all Series and is listed in each respective
product section.
See pages 6-41 for herm seal, 42-50 for axial and
radial molded, and 61-70 for tantalum dipped.
1
It is usually most convenient to translate the permis-
sible power into an AC voltage rating. Assuming a sinu-
soidal waveform, the “ripple voltage” permissible may be
calculated from the impedance and ESR data shown in the
respective product section. However, three criteria must
be observed:
0.3
0.1
6
8
µ
F
d
100
1000
10K
100K
1M
10M
Frequency (MHz)
ESR and Impedance vs. Frequency
Figure 10.
78
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