Application Notes

For technical support and more information, see inside back cover or visit www.ti.com

Table 4-1: Input/Output Capacitors

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

Capacitor Recommendations for

the

PT5820 Regulator Series

Input Capacitor:

The recommended input capacitance is determined by

1.3 ampere minimum ripple current rating and 560µF

minimum capacitance.

Ripple current and <100m

Ω equivalent series resistance

(ESR) values are the major considerations, along with

temperature, when designing with different types of

capacitors. Tantalum capacitors have a recommended

minimum voltage rating of twice the maximum DC

voltage + AC ripple. This is necessary to insure reli-

ability for input voltage bus applications.

Output Capacitors:

The maximum allowable ESR of the output capacitor is

150m

Ω. Electrolytic capacitors have marginal ripple

performance at frequencies greater than 400kHz but

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 low ESR type capacitor

part numbers are identified in Table 4-1.

PT5820 Series

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

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.

Capacitor Table

Table 1 identifies the characteristics of capacitors from a

number of vendors with acceptable ESR and ripple cur-

rent (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

(Equivalent Series Resistance at 100kHz) are critical parameters

necessary to insure both optimum regulator performance and

long capacitor life.

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