TAJA105K025RNJ Datasheet, PDF (47/51 Pages) AVX Corporation – Surface Mount Tantalum Capacitors

Questions & Answers
Some commonly asked questions regarding Tantalum
Capacitors:
Question: If I use several tantalum capacitors in serial/parallel
combinations, how can I ensure equal current and voltage
sharing?
Answer: Connecting two or more capacitors in series
and parallel combinations allows almost any value
and rating to be constructed for use in an application. For
example, a capacitance of more than 60µF is required in a
circuit for stable operation. The working voltage rail is 24
volts dc with a superimposed ripple of 1.5 volts at 120 Hz.
The maximum voltage seen by the capacitor is Vdc +
Vac=25.5V
Applying the 50% derating rule tells us that a 50V
capacitor is required.
Connecting two 25V rated capacitors in series will
give the required capacitance voltage rating, but the
The two resistors are used to ensure that the leakage
currents of the capacitors does not affect the circuit
reliability, by ensuring that all the capacitors have half
the working voltage across them.
Question: What are the advantages of tantalum over other
capacitor technologies?
Answer:
1. Tantalum capacitors have high volumetric efficiency.
2. Electrical performance over temperature is very
stable.
3. They have a wide operating temperature range -55
degrees C to +125 degrees C.
4. They have better frequency characteristics than
aluminum electrolytics.
5. No wear out mechanism. Because of their construction,
solid tantalum capacitors do not degrade in perfor-
mance or reliability over time.
33µF
25V
¬
33µF
25V
16.5µF
50V
effective capacitance will be halved, so for greater than 60µF,
four such series combinations are required, as shown.
33µF
25V
¬
66µF
50V
In order to ensure reliable operation, the capacitors should
be connected as shown below to allow current sharing of
the ac noise and ripple signals. This prevents any one
capacitor heating more than its neighbors and thus being
the weak link in the chain.
+
•
•
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Question: How does TPS differ from your standard
product?
Answer: TPS has been designed from the initial anode
production stages for power supply applications. Special
manufacturing processes provide the most robust capacitor
dielectric by maximizing the volumetric efficiency of the
package. After manufacturing, parts are conditioned by
being subjected to elevated temperature overvoltage burn in
applied for a minimum of two hours. Parts are monitored on
a 100% basis for their direct current leakage performance at
elevated temperatures. Parts are then subjected to a low
impedance current surge. This current surge is performed on
a 100% basis with each capacitor individually monitored.
At this stage, the capacitor undergoes 100% test for
capacitance, Dissipation Factor, leakage current, and
100 KHz ESR to TPS requirements.
Question: If the part is rated as a 25 volt part and you have
current surged it, why can’t I use it at 25 volts in a low
impedance circuit?
Answer: The high volumetric efficiency obtained using
tantalum technology is accomplished by using an extremely
thin film of tantalum pentoxide as the dielectric. Even
an application of the relatively low voltage of 25 volts will
produce a large field strength as seen by the dielectric. As a
result of this, derating has a significant impact on reliability as
described under the reliability section. The following example
uses a 22 microfarad capacitor rated at 25 volts to illustrate
the point. The equation for determining the amount of
surface area for a capacitor is as follows:
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