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Application Notes

Table 1: Input/Output Capacitors

(1) N/R –Not recommended. The surge and normal voltage rating does not meet the minimum operating limits.

Capacitor Recommendations for

the

PT5540 Boost Regulator Regulator Series

Input Capacitors:

The minimum input capacitance required is 100µF, with

a 200-mA(rms) ripple current rating and 150m

Ω typical

equivalent series resistance (ESR). Electrolytic capacitors

have marginal ripple performance at frequencies greater

than 400kHz but have excellent low-frequency transient

response. 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. Preferred ESR type capacitor

part numbers are identified in Table 2-1.

Output Capacitor:

The recommended output capacitance is determined by

0.5-A(rms) ripple current rating and 100µF minimum

capacitance. The maximum output capacitance is 560µF.

Ripple current and >50m

Ω ESR value are the major

considerations, along with temperature, when designing

with different types of capacitors. Tantalum capacitors

have a recommended minimum voltage rating of 2

× (the

maximum DC voltage + AC ripple). This is necessary to

insure reliability for input voltage bus applications.

PT5540 Series

Tantalum Capacitors (Optional Input Capacitors)

Tantalum type capacitors can be used for the input bus

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

T495/T510 series. These capacitors are recommended

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

dissipation, and lower ripple current capability. The TAJ

series is less reliable than the AVX TPS series when deter-

mining power dissipation capability. Tantalum or Oscon®

types are recommended for applications where ambient

temperatures fall below 0°C. Do not use tantalum capaci-

tors on the output bus.

Capacitor Table

Table 1 identifies the characteristics of capacitors from a

number of vendors with acceptable ESR and ripple current

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

(Equivalent Series Resistance at 100kHz) are critical parameters

necessary to insure both optimum regulator performance and

long capacitor life.

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