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CAPACITOR RECOMMENDATIONS for the PTH04070W WIDE-OUTPUT

Input Capacitor

Output Capacitors

Ceramic Capacitors

Tantalum Capacitors

Capacitor Table

PTH04070W

SLTS227B – SEPTEMBER 2004 – REVISED OCTOBER 2007

ADJUST POWER MODULES

The minimum recommended input capacitor(s) is 47-

μF of ceramic capacitance, in either an X5R or X7R

temperature tolerance. The ceramic capacitors should be located within 0.5 in. (1,27 cm) of the regulator's input

pins. Electrolytic capacitors can also be used at the input, but only in addition to the required ceramic

capacitance. The minimum ripple current rating for nonceramic capacitors should be at least 200 mA rms. The

ripple current rating of electrolytic capacitors is a major consideration when they are used at the input.

When specifying regular tantalum capacitors for use at the input, a minimum voltage rating of 2

× (maximum dc

voltage + ac ripple) is highly recommended. This is standard practice to ensure reliability. Polymer-tantalum

capacitors are not affected by this requirement.

For improved ripple reduction on the input bus, additional ceramic capacitors can be used to complement the

minimum requirement.

For most applications only one (1) 47-

μF ceramic capacitor is required. The ceramic capacitor should be located

within 0.5 in. (1,27 cm) of the output pin. Adding a second 47-

μF nonceramic capacitor allows the module to

meet its transient response specification. For applications with load transients (sudden changes in load current),

the regulator response benefits from additional external output capacitance. A high-quality computer-grade

electrolytic capacitor should be adequate.

Electrolytic capacitors should be located close to the load circuit. These capacitors provide decoupling over the

frequency range, 2 kHz to 150 kHz. Aluminum electrolytic capacitors are suitable for ambient temperatures

above 0

°C. For operation below 0°C, tantalum 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 mΩ using the

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

Table 3, the recommended capacitor table.

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 must be added.

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

regulator. When placed at the output their combined ESR is not critical as long as the total value of ceramic

capacitance does not exceed 200

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

three identical ceramic capacitors with values of 10

μF or greater in parallel.

Additional 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/T520 capacitors series are suggested over many other tantalum types due

to their 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.

The capacitor table, 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 rating

and ESR (at 100 kHz) are critical parameters necessary to insure both optimum regulator performance and long

capacitor life.

Copyright © 2004–2007, Texas Instruments Incorporated

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