Application Notes

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

PT7761, PT7769

Capacitor Recommendations for

the

PT7761 Integrated Switching Regulator

Input Capacitors

The recommended input capacitance is determined by

1.4 ampere minimum ripple current rating and 1500µF

minimum capacitance. Capacitors listed below must be

rated for a minimum of 2x the input voltage with +5V

operation. Ripple current and

≤100mΩ Equivalent Series

Resistance (ESR) values are the major considerations along

with temperature when selecting the proper capacitor.

Output Capacitors

The minimum required output capacitance is 330µF with

a maximum ESR less than or equal to 100m

Ω. Failure to

observe this requirement may lead to regulator instability or

oscillation. Electrolytic capacitors have poor ripple perfor-

mance at frequencies greater than 400kHz, but excellent low

frequency transient response. Above the ripple frequency

ceramic decoupling capacitors are necessary to improve the

transient response and reduce any microprocessor high

frequency noise components apparent during higher current

excursions. Preferred low ESR type capacitor part numbers

are identified in the Table 1 below.

Note: (N/R) is not recommended for this application, due to extremely low Equivalent Series Resistance (ESR)

Table 1 Capacitors Characteristic Data

Tantalum Characteristics

Tantalum capacitors with a minimum 10V rating are

recommended on the output bus, but only the AVX TPS

series, Sprague 594/595 series, or Kemet T495/T510

series. These AVX, Sprague, and Kemet capacitors are

specified over other types due to their higher surge current,

excellent power dissipation, and ripple current ratings. As a

caution, the TAJ series by AVX is not recommended. This

series exhibits considerably higher ESR, reduced power

dissipation and lower ripple current capability. The TAJ

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

mining power dissipation capability.

Capacitor Table

Table 1 identifies the characteristics of capacitors from a

number of vendors with acceptable ESR and ripple current

(rms) ratings. The suggested minimum quantities per regu-

lator for both the input and output buses are identified.

This is not an extensive capacitor list. The table below is a

selection guide for input and output capacitors. Other capacitor

vendors are available with comparable RMS ripple current rating

and ESR (Equivalent Series Resistance at 100kHz). These

critical parameters are necessary to insure both optimum regulator

performance and long capacitor life.

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