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CAPACITOR RECOMMENDATIONS FOR THE PTH12030 SERIES OF POWER MODULES

INPUT CAPACITOR

OUTPUT CAPACITORS (OPTIONAL)

CERAMIC CAPACITORS

TANTALUM CAPACITORS

CAPACITOR TABLE

PTH12030W/L

SLTS211F – MAY 2003 – REVISED FEBRUARY 2007

The recommended input capacitor(s) is determined by the 560 µF minimum capacitance and 500 mArms

minimum ripple current rating.

Ripple current, less than 100 m

Ω equivalent series resistance (ESR) and temperature, are the major

considerations when selecting input capacitors. Unlike polymer-tantalum capacitors, regular tantalum capacitors

are not recommended for the input bus. These capacitors require a recommended minimum voltage rating of 2

×

(max. dc voltage + ac ripple). When the operating temperature is below 0

°C, the ESR of aluminum electrolytic

capacitors increases. For these applications, Os-Con, polymer-tantalum, and polymer-aluminum types should be

considered.

Adding one or two ceramic capacitors to the input further reduces high-frequency reflected ripple current.

For applications with load transients, regulator response benefits from an external output capacitance. The

recommended output capacitance of 330 µF allows the module to meet its transient response specification. For

most applications, a high quality computer-grade aluminum eletrolytic capacitor is adequate. These capacitors

provide decoupling over the frequency range, 2 kHz to 150 kHz, and are suitable when ambient temperatures

are above 0

°C. For operation below 0°C, tantalum, ceramic, or Os-Con type capacitors are recommended.

When using one or more nonceramic capacitors, the calculated equivalent ESR should be no lower than 4 m

Ω

(7 m

Ω using the manufacturer’s maximum ESR for a single capacitor). A list of preferred low-ESR type

capacitors are identified in Table 4.

Above 150 kHz, the performance of aluminum electrolytic capacitors is less effective. Multilayer ceramic

capacitors have low ESR and a resonant frequency higher than the bandwidth of the regulator. They can be

used to reduce the reflected ripple current at the input as well as improve the transient response of the output.

When used on the output their combined ESR is not critical as long as the total value of ceramic capacitance

does not exceed 300 µF. Also, to prevent the formation of local resonances, do not place more than five

identical ceramic capacitors in parallel with values of 10 µF or greater.

Tantalum type capacitors can only be used on the output bus, and are recommended for applications where the

ambient operating temperature can be less than 0

°C. The AVX TPS, Sprague 593D/594/595, and Kemet

T495/T510 capacitor series are suggested over other tantalum types due to their higher rated surge, power

dissipation, and ripple current capability. As a caution many general-purpose tantalum capacitors have

considerably higher ESR, reduced power dissipation and lower ripple current capability. These capacitors are

also less reliable as they have reduced power dissipation and surge current ratings. Tantalum capacitors that

have no stated ESR or surge current rating are not recommended for power applications.

When specifying Os-con and polymer tantalum capacitors for the output, the minimum ESR limit is encountered

well before the maximum capacitance value is reached.

Table 4 identifies the characteristics of capacitors from a number of vendors with acceptable ESR and ripple

current (rms) ratings. The recommended 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 (at 100 kHz) are critical

parameters necessary to insure both optimum regulator performance and long capacitor life.

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