Application Notes

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Table 1: Input/Output Capacitors

ATH10T033/T05: Capacitor Recommendations

Input Capacitor

The recommended input capacitor(s) is determined by

330 µF minimum capacitance, and 500 mA rms mini-

mum ripple current rating.

Ripple current and <150 m

Ω equivalent series resistance

(ESR) values are the major considerations, along with

temperature, when designing with different types of capaci-

tors. Tantalum capacitors have a recommended minimum

voltage rating of twice 2

× (the maximum DC voltage +

AC ripple). This is standard practice for tantalum capaci-

tors to insure reliability.

Output Capacitors (Optional)

The ESR of the bulk (non-ceramic) capacitors must be

equal to, or less than 150 m

Ω. Electrolytic capacitors

have marginal ripple performance at frequencies greater

than 400 kHz but excellent low frequency transient re-

sponse. Above the ripple frequency, ceramic capacitors are

necessary to improve the transient response and reduce

any high frequency noise components apparent during

higher current excursions.

Tantalum Capacitors

Tantalum type capacitors can be used for the output but

only the AVX TPS, Sprague 593D/594/595 or Kemet

T495/T510 series. These capacitors are recommended

ATH10T033 & ATH10T05 Series

over many other tantalum types due to their higher rated

surge, power dissipation, and ripple current capability. As a

caution the TAJ series by AVX is not recommended. This

series has considerably higher ESR, reduced power dissipa-

tion, and lower ripple current capability. The TAJ series

is less reliable than the AVX TPS series when determin-

ing power dissipation capability. Tantalum or Oscon®

types are recommended for applications where ambient

temperatures fall below 0 °C.

Ceramic Capacitors

Ceramic capacitors will compliment electrolytic types.

Adding 10 µF to 47 µF of ceramic capacitance will reduce

ripple on the input and output bus. Output ripple and

transient measurement accuracy is improved by measur-

ing directly across a 10 µF ceramic capacitor.

Capacitor Table

Table 2-1 identifies the characteristics of capacitors from a

number of vendors with acceptable ESR and ripple current

(rms) ratings. The number of capacitors required at both

the input and output buses is identified for each capacitor

type.

This is not an extensive capacitor list. Capacitors from other

vendors are available with comparable specifications. Those listed

are for guidance. The RMS ripple current rating and ESR

(at 100 kHz) are critical parameters necessary to insure both

optimum regulator performance and long capacitor life.

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