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APPLICATION INFORMATION

CAPACITOR RECOMMENDATIONS FOR THE PTH05T210W POWER MODULE

Input Capacitor (Required)

TurboTrans Output Capacitor

Non-TurboTrans Output Capacitor

PTH05T210W

SLTS263D – NOVEMBER 2005 – REVISED OCTOBER 2006

The size and value of the input capacitor is determined by the converter’s transient performance capability. The

minimum amount of required input capacitance is 1000 µF, with an RMS ripple current rating of 1000 mA. This

minimum value assumes that the converter is supplied with a responsive, low inductance input source. This

source should have ample capacitive decoupling, and be distributed to the converter via PCB power and ground

planes.

For high-performance/transient applications, or wherever the input source performance is degraded, 2000 µF of

input capacitance is recommended. The additional input capacitance above the minimum level insures an

optimized performance.

Ripple current (rms) rating, less than 100 m

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

main considerations when selecting input capacitors. The ripple current reflected from the input of the

PTH05T210W module is moderate to low. Therefore any good quality, computer-grade electrolytic capacitor has

an adequate ripple current rating.

Regular tantalum capacitors are not recommended for the input bus. These capacitors require a recommended

minimum voltage rating of 2

× (maximum dc voltage + ac ripple). This is standard practice to ensure reliability.

No tantalum capacitors were found with a sufficient voltage rating to meet this requirement. When the operating

temperature is below 0

°C, the ESR of aluminum electrolytic capacitors increases. For these applications,

Os-Con, poly-aluminum, and polymer-tantalum types should be considered. Adding one or two ceramic

capacitors to the input attenuates high-frequency reflected ripple current.

The PTH05T210W requires a minimum output capacitance of 470

µF. The required capacitance above 470µF is

determined by actual transient deviation requirements.

TurboTrans allows the designer to optimize the capacitance load according to the system transient design

requirement. High quality, ultra-low ESR capacitors are required to maximize TurboTrans effectiveness.

Capacitors with a capacitance (

µF) × ESR (mΩ) product of ≤ 10,000 mΩ×µF are required.

Working Example:

A bank of 6 identical capacitors, each with a capacitance of 680

µF and 5 mΩ ESR, has a C × ESR product of

3400

µFxmΩ (680 µF × 5 mΩ).

Using TurboTrans in conjunction with the high quality capacitors (capacitance (

µF) × ESR (mΩ)) reduces the

overall capacitance requirement while meeting the minimum transient amplitude level.

Table 1 includes a preferred list of capacitors by type and vendor. See the Output Bus / TurboTrans column.

Note: See the TurboTrans Technology Application Notes within this document for selection of specific

capacitance.

The PTH05T210W requires a minimum output capacitance of 470

µF. Non-TurboTrans applications must

observe minimum output capacitance ESR limits.

A combination of 200 µF of ceramic capacitors plus low ESR (15 m

Ω to 30 mΩ) Os-Con electrolytic/tantalum

type capacitors can be used. When using Polymer tantalum types, tantalum type, or Oscon types only, the

capacitor ESR bank limit is 3 m

Ω to 5 mΩ. (Note: no ceramic capacitors are required). This is necessary for the

stable operation of the regulator. Additional capacitance can be added to improve the module's performance to

load transients. High quality computer-grade electrolytic capacitors are recommended. Aluminum electrolytic

capacitors provide adequate decoupling over the frequency range, 2 kHz to 150 kHz, and are suitable when

ambient temperatures are above -20

°C. For operation below -20°C, tantalum, ceramic, or Os-Con type

capacitors are necessary.

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