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

Table 1: Input/Output Capacitors

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

Capacitor Recommendations for

the

Dual-Output PT6935 Regulator Series

Input Capacitors:

The recommended input capacitance is determined by 1.0

ampere minimum ripple current rating and 330µF minimum

capacitance (300µF for Oscon® or low ESR tantalum).

Ripple current and <100m

Ω equivalent series resistance

(ESR) values are the major considerations, along with tem-

perature, 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 applica-

tions

than 150m

Ω. Electrolytic capacitors have poor ripple per-

formance at frequencies greater than 400kHz but excellent

low frequency transient response. Above the ripple fre-

quency, 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

have an ESR of up to 200m

Ω for optimum performance

and ripple reduction. (Note: Vendor part numbers for the

PT6935 Series

Tantalum Capacitors

Tantalum type capacitors can be used for the output but only

the AVX TPS series, Sprague 593D/594/595 series 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 dissipa-

tion, and lower ripple current capability. The TAJ series is

less reliable than the AVX TPS series when determining

power dissipation capability. Tantalum or Oscon® types

are recommended for applications where ambient tem-

peratures fall below 0°C.

Capacitor Table

Table 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

(Equivalent Series Resistance at 100kHz) are critical parameters

necessary to insure both optimum regulator performance and

long capacitor life.

Application Notes

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5

Not Recommended For New Designs