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Application Notes
9
Table 1 Capacitors Characteristic Data
Capacitor Recommendations for
the Non-Isolated
40-A Excalibur Series of Regulators
Input Capacitors
The recommended input capacitance is determined by the
1.0 ampere minimum ripple current rating and 1500F
minimum capacitance. Capacitors listed below must be
rated for a minimum of 2× the input voltage with +5V
operation. Ripple current and
≤100m equivalent series
resistance (ESR) values are the major considerations along
with temperature when selecting the proper capacitor.
Output Capacitors
The minimum required output capacitance is either 660F
Oscon/Tantalum or 1200F Alunimun Electrolytic with
a maximum ESR less than or equal to 100m
. Failure
to observe this requirement may lead to regulator insta-
bility or oscillation. Electrolytic capacitors have poor
ripple performance at frequencies greater than 400kHz,
but excellent low frequency transient response. Above
the ripple frequency ceramic decoupling capacitors are
necessary to improve the transient response and reduce
any high frequency noise components apparent during
higher current excursions. Preferred low ESR type
capacitor part numbers are identified in Table 1 below.
Tantalum Characteristics
Tantalum capacitors with a minimum 10V rating are
recommended on the output bus, but only the AVX TPS,
Sprague 594/595, or Kemet T495/T510 product series.
The AVX TPS, Sprague, or Kemet series capacitors are
specified over other types due to their higher surge current,
excellent power dissipation, and ripple current ratings.
As a caution, the TAJ Series by AVX is not recommended.
This series exhibits considerably higher ESR, reduced
power dissipation and lower ripple current capability.
The TAJ series is also less reliable compared to the TPS
series when determining power dissipation capability.
Capacitor Table
Table 1 identifies the characteristics of capacitors from a
number of vendors with acceptable ESR and ripple current
(rms) ratings. The suggested minimum quantities per regu-
lator for both the input and output buses are identified.
This is not an extensive capacitor list. The table below is a
suggested selection guide for input and output capacitors. Other
capacitor vendors are available with comparable RMS ripple
current rating and ESR (Equivalent Series Resistance at 100kHz).
These critical parameters are necessary to insure both opti-
mum regulator performance and long capacitor life.
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