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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 1500µF

minimum capacitance. Capacitors listed below must be

operation. Ripple current and

≤100mΩ 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 660µF

Oscon/Tantalum or 1200µF Alunimun Electrolytic with

a maximum ESR less than or equal to 100m

Ω. 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.

PT8100

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