Application Notes

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 ripple current rating and ESR does not meet the requirements.

Capacitor Recommendations for

the PT6520 Series of

Integrated Switching Regulators

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 temperature, when designing with different

types of capacitors. Tantalum capacitors have a recom-

mended minimum voltage rating of 2

× the maximum

DC voltage + AC ripple. This is necessary to insure

reliability for input voltage bus applications

Output Capacitors:

greater than 150m

Ω. Electrolytic capacitors have poor

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 1.

PT6520 Series

Tantalum Capacitors

Tantalum type capacitors may be used for the output but

only the AVX TPS series, Sprague 593D/594/595 series

or Kemet T495/T510 series. These capacitors are rec-

ommended 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 determining power dissipation capability.

Tantalum or Oscon® types are recommended for appli-

cations 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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