2020©
Tantalum Polymer vs Aluminum Polymer
Performance as an Output Filter Capacitor
for Miniature Switching Power Supplies
R. Demcko
A. Stanziola
D. West
AVX Corporation
One AVX Boulevard
Fountain Inn, S.C. 29644 USA
Abstract
Engineers have questioned the impact performance of converting
Aluminum Polymer capacitors to Tantalum Polymer capacitors in
applications where MLCCs are present on the output lter ‘bank’ of a
small switching power supply. The reasons for designers to convert
to Tantalum Polymer capacitors in the design ranged from long term
reliability and stability to availability/delivery and company specic
design guidelines.
This investigation is intended to compare the interchangeability of
Tantalum Polymer Capacitors in a design with the original Aluminum
Polymer capacitors. The data collected was the measured output
voltage ripple on a highly utilized circuit/chipset under a specic
conditions of an end user. Comparisons between Aluminum Polymer
Electrolytic and Tantalum Polymer Electrolytic technologies are made.
TECHNICAL
PAPER
A common theme present in electronic designs is
smaller, lighter, more functionality, more reliability
and lower costs. Power supplies have a difcult
goal to deliver given that the semiconductor’s load
power requirements in the circuit have become
more power hungry and tolerate less ripple since
Vcc levels are constantly dropping though many
times reverting to multiple Vcc rail levels.
Luckily the use of switching power supplies can
deliver higher power conversion efciency along
with reduced size & weight when compared
to other solutions. Its because of this that IC
houses have concentrated efforts on creating
chipsets intended to provide a simple switching
implementation with a single chip or two.
Switchers can pose problems in terms of noise
and output ripple but thanks to progress made in
designs, simulations and capacitor technology –
switchers are here to stay.
Many times the output lters consist of ceramic
capacitors for high frequency noise ltering and
bulk capacitors for low frequency ltering / large
curent hold up functions. A typical schematic is
shown in gure 1.
Ron.Demcko@avx.com
This study concentrates on dening bulk lter
capacitors performance & its impact upon ripple.
As IC rail voltages decrease, the amount of
acceptable ripple voltage decreases. Therefore
output capacitor performance is an enabling
feature to a successful low ripple switcher.
Bulk capacitors have made trememdous
progress in recent years based upon demands
from high volume end users across the spectrum
of electronics. This comparison will only look at
conductive tantalum polymer and conductive
aluminum polymer capacitors.
Stacked MLCC capacitors were not considered
in this investigation due to the end circuits small
size and small power rating.
It is important to note that stacked ceramic
capacitors do not necessarily exhibit excessive
DC bias instability effects. This is a common
misconception associated with stacked ceramic
output lter capacitors. DC bias instability is
a direct function of ceramic dielectric type
chosen to build the ceramic capacitors. Class I
ceramic dielectrics exist which exhibit zero DC
bias characteristics to high DC bias instability.
However, stacked ceramic capacitors were not
considered due to the nature of the test circuit.
Figure 1 Output Filter Capacitor Schematic
Ashley.Stanziola@avx.com Daniel.West@avx.com