Application Notes

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

Table 3-1; Input/Output Capacitors

Capacitor Recommendations for the PT5800 &

PT5810 Step-Down Regulator Series

Input Capacitor:

The recommended input capacitance is determined by a

700-mA ripple current rating and the following minimum

capacitance requirements.

• PT5800 = 820 µF minimum capacitance

• PT5810 = 1000 µF minimum capacitance

Ripple current and <100 m

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 ensure reliabil-

ity for input voltage bus applications

Output Capacitors

The ESR of the capacitors is less than 100m

Ω. Electrolytic

capacitors have marginal ripple performance at frequen-

cies greater than 400 kHz, but excellent low frequency

transient response. Above the ripple frequency ceramic

capacitors are necessary. Ceramic capacitors improve the

transient response and reduce any high frequency noise

components apparent during high current excursions.

Preferred low-ESR electrolytic capacitor part numbers

are identified in Table 3-1.

PT5800/5810 Series

Tantalum Capacitors (Optional Output 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 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 capa-

bility. Tantalum or Oscon® types are recommended for

applications where ambient temperatures fall below 0°C.

Capacitor Table

Table 2-1 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 100 kHz are critical param-

eters necessary to insure both optimum regulator performance

and long capacitor life.

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