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Capacitor Recommendations for the PTV12010 Series of Power Modules

Input Capacitors

Output Capacitor (Optional)

Ceramic Capacitors

Tantalum Capacitors

PTV12010L

PTV12010W

SLTS234B – DECEMBER 2004 – REVISED FEBRUARY 2007

The required input capacitors are a combination of a 10-µF X5R/X7R ceramic, and a 100-µF electrolytic type.

output voltage and current limits for a capacitor's rms ripple current rating. The ripple current requirements for

the electrolytic capacitance are conditional that the 10-µF ceramic capacitor is present.

The 10-µF ceramic capacitor is necessary to reduce both the magnitude of ripple current through the electroytic

capacitor and the amount of ripple current reflected back to the input source. Ceramic capacitors should be

located within 0.5 in. (1,3 cm) of the module input pins. Additional ceramic capacitors can be added to reduce

the RMS ripple current requirement for the electrolytic capacitor.

Ripple current (Arms) rating, less than 100 m

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

major considerations when selecting input capacitors. Regular tantalum capacitors have a recommended

minimum voltage rating of 2 × (max. dc voltage + ac ripple). This is standard practice to ensure reliability. Only a

few tantalum capacitors were found to have 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 optional value defined is only required to meet 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 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.

In addition to electrolytic capacitance, adding a 10–µF ceramic capacitor across the output will further reduce the

output ripple voltage and improve 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 low ESR and a resonant frequency higher than the bandwidth of the regulator. They are

recommended 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 approximately 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 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

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

before the maximum capacitance value is reached.

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