What is a Tantalum
Capacitor?
Tantalum
capacitors are electrolytic capacitors that use tantalum metal for the
anode. They are polarized capacitors with superior frequency and stability
characteristics.
What makes tantalum capacitors unique is the usage of
tantalum for the anode of the device. This anode is set up as one chunk of
material inside of the case, which is very different from the layering style
used in MLCC capacitors where the material is sandwiched on itself and then
capped on the ends. Using tantalum results in a very thin dielectric layer,
resulting in a higher capacitance per volume and allowing for smaller
capacitors that can still meet the needs of modern systems. In addition to the
nice gain in capacitance per volume, the tantalum capacitors also have very low
ESR or Equivalent Series Resistance reducing system losses. A downside of low
ESR is that it may be too low to achieve stability in power supply regulators,
which needs to be taken into account.
Why Use Tantalum Capacitors?
The
tantalum capacitor also has excellent stability characteristics. The tantalum
capacitor will maintain the expected capacitance better. With this stability
you get more of the expected behavior of your system, which is especially
important for filters; if the capacitance varies too much you may lose frequencies
you desire. Beyond the electrical differences the construction of the tantalum
capacitor also makes it highly resistant to vibration issues, improving overall
system reliability.
The
previous characteristics show how tantalum
capacitors can be uniquely suited to help in modern electronics, but they
are not without their quirks and there are a couple of major ones to take into
account when you want to design these in. Tantalum capacitors are generally
polarized devices, meaning that during layout and assembly you need to pay more
attention to their orientation. This makes them a little more work than a
regular ceramic capacitor, which is just a trait of electrolyte base
capacitors. When putting tantalum capacitors into a system, you also need to
watch out for their failure modes.
Tantalum Capacitor Failure Modes
Tantalum
capacitors have a potentially dangerous failure mode. In case of voltage
spikes, the tantalum anode could are available contact with the manganese
dioxide cathode, and if the energy of the spike is sufficient it should begin a
chemical reaction. This chemical process manufactures heat and is
self-sustaining and will produce smoke and flame. To prevent this thermal
runaway from happening, external failsafe electronic equipment like current
limiters and thermal fuses should be utilized in conjunction with tantalum
capacitors.
When to Use a Tantalum Capacitor?
So
when do you want to use a tantalum
capacitor? When you need maximum capacitance in a small space like
decoupling next to a microchip, excellent stability over a range of
temperatures or voltages, and you are aware of their unique characteristics so
they can be designed in properly and not risk your system with a fiery failure.
Tantalum Capacitor advantages
· High volumetric
capacitance
· High capacitance
per unit weight
· Reliable when
used within electrical limits
· Cost effective
· Available in SMD
format
· Wide operating
temperature range
Tantalum Capacitor disadvantages
· Must be used
within its electrical limits otherwise it can fail catastrophically.
· High voltages and
very high capacitance levels not normally available.
· Does not like
voltage above limits
· Does not like
reverse bias
· Low ripple
current rating
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