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CAPACITOR RECOMMENDATIONS FOR THE PTH03050W AND PTH05050W

Input Capacitor

Output Capacitors (Optional)

Ceramic Capacitors

Tantalum Capacitors

Capacitor Table

PTH05050W

SLTS213D – MAY 2003 – REVISED JUNE 2007

The recommended input capacitor(s) is determined by the 100

µF minimum capacitance and 300 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, regular tantalum capacitors have a

recommended minimum voltage rating of 2

×(maximum DC voltage + AC ripple). This is standard practice to

ensure reliability.

For improved ripple reduction on the input bus, ceramic capacitors may used to compliment electrolytic types to

achieve the minimum required capacitance.

For applications with load transients (sudden changes in load current), regulator response will benefit from an

external output capacitance. The recommended output capacitance of 100

µF will allow the module to meet its

transient response specification (see product data sheet). 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. For operation below 0°C tantalum,

ceramic or OS-CON type capacitors are recommended. When using one or more non-ceramic capacitors, the

calculated equivalent ESR should be no lower than 4 m

Ω (7 mΩ using the manufacturer's maximum ESR for a

single capacitor). A list of preferred low-ESR type capacitors are identified in Table 3.

Above 150 kHz the performance of aluminum electrolytic capacitors becomes less effective. To further improve

the reflected input ripple current or the output transient response, multilayer ceramic capacitors can also be

added. Ceramic capacitors have very low ESR and their resonant frequency is higher than the bandwidth of the

regulator. 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 be used at both the input and output, 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 many 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 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 will be

encountered well before the maximum capacitance value is reached.

Table 3 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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