PTH12030W/L
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SLTS211F–MAY 2003–REVISED FEBRUARY 2007
CAPACITOR RECOMMENDATIONS FOR THE PTH12030 SERIES OF POWER MODULES
INPUT CAPACITOR
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 mΩ 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.
OUTPUT CAPACITORS (OPTIONAL)
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 mΩ
(7 mΩ using the manufacturer’s maximum ESR for a single capacitor). A list of preferred low-ESR type
capacitors are identified in Table 4.
CERAMIC CAPACITORS
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 CAPACITORS
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.
CAPACITOR TABLE
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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