Application Notes

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Capacitor Recommendations for

the PT6340

6A Excalibur™ Regulator Series

Input Capacitors:

Output Current

≤≤≤≤≤4A Continuous (Table 1)

The recommended input capacitance is determined by

740 milli-amperes (rms) minimum ripple current rating,

less than 100m

Ω ESR (equivalent series resistance),

and 100µF minimum capacitance. The ripple current

rating, ESR, and operating temperature are the major

considerations when selecting the input capacitor.

It is recommended that tantalum capacitors have a

minimum voltage rating of twice (2

×) the maximum dc

voltage, plus the ac ripple. This is necessary to insure

reliability with 12V input voltage bus applications. None

of the 100µF tantalum capacitors were found to meet

this requirement.

Input Capacitors:

Output Current

>>>>>4A Continuous (Table 2)

The recommended input capacitance is determined by

1.0 amperes (rms) minimum ripple current rating and

100µF minimum capacitance. The ripple current rating,

combined with less than 100m

Ω ESR (equivalent series

resistance) value are the major considerations, along

with temperature, when selecting the input capacitor.

It is recommended that tantalum capacitors have a

minimum voltage rating of twice (2

×) the maximum dc

voltage, plus the ac ripple. This is necessary to insure

reliability for 12V input voltage bus applications. None

of the 100µF tantalum capacitors were found to meet

this requirement.

Output Capacitors:

Output Current 0–6A (Table 1 & Table 2)

The ESR of the required capacitor must be less than,

or equal to 50m

Ω. Electrolytic capacitors have poor

ripple performance 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 high frequency noise components apparent during

higher current excursions. Preferred low ESR type

capacitor’s part numbers are identified in the capacitor

tables.

PT6340 Series

Tantalum Capacitors

Tantalums are acceptable on the output bus but only the

AVX TPS series, Sprague 593D/594/595 series or Kemet

T495/T510 series. These capacitors are recommended

over many other 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 exhibits considerably higher ESR and lower ripple

current capability. The TAJ series is also less reliable than

the TPS series when determining power dissipation

capability. Tantalum or Oscon capacitor types are recom-

mended for applications where ambient temperatures fall

below 0°C.

Capacitor Tables

Table 1 and Table 2 identify the vendors with acceptable

ESR and maximum allowable ripple current (rms) ratings.

The output capacitors are identified in both tables under

the “Output Bus” column with the required quantity.

The input capacitors are listed in both tables. Table 1 has

the recommended input capacitors when operating the

ISR at a load current of 4Adc or less, and Table 2 identi-

fies input capacitors for ISR load currents greater than

4Adc.

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.