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APPLICATION INFORMATION

CAPACITOR RECOMMENDATIONS FOR THE PTH12060 SERIES OF POWER MODULES

Input Capacitor

Output Capacitors (Optional)

Ceramic Capacitors

Tantalum Capacitors

Capacitor Table

PTH12060W/L

SLTS217D–MAY 2003–REVISED OCTOBER 2005

The recommended input capacitance is determined by the 560 µF minimum capacitance and 1050 mArms

minimum ripple current rating. A 10 µF X5R/X7R ceramic capacitor can be added to reduce the reflected input

ripple current. The ceramic capacitor should be located between the input electrolytic and the module.

Ripple current, less than 100 mΩ equivalent series resistance (ESR) and temperature, are major considerations

when selecting input capacitors. Unlike polymer-tantalum capacitors, regular tantalum capacitors have a

recommended minimum voltage rating of 2 × (max. dc voltage + ac ripple). No tantalum capacitors were found

with sufficient voltage rating to meet this requirement. At temperatures below 0°C, the ESR of aluminum

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

should be considered.

For applications with load transients (sudden changes in load current), regulator response benefits from external

output capacitance. The value of 330 µF is used to define the transient response specification. For most

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

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

above 0°C. 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 mΩ (7 mΩ using the

manufacturer's maximum ESR for a single capacitor). A list of preferred low-ESR type capacitors are identified in

In addition to electrolytic capacitance, adding a 10 µF X5R/X7R ceramic capacitor to the output reduces the

output ripple voltage and improves the regulator's transient response. The measurement of both the output ripple

and transient response is also best achieved across a 10 µF ceramic capacitor.

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

capacitors have a 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, and 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 are most suited for use 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 lower power dissipation and surge current ratings. Tantalum capacitors that do not

have a 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.

current (rms) ratings. The recommended number of capacitors required at both the input and output buses is

identified for each capacitor type.

Note: 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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