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Output Capacitor (Required)

Output Capacitor Information

TurboTrans Output Capacitance

Non-TurboTrans Output Capacitance

PTH08T260W, PTH08T261W

SLTS272A – DECEMBER 2006 – REVISED MAY 2007

The PTH08T261W requires a minimum output capacitance of 200

µF of ceramic type.

The PTH08T260W requires a minimum output capacitance of 100

µF ceramic and 100 µF non-ceramic.

Additional non-ceramic, low-ESR capacitance is recommended for improved performance. See the Electrical

Characteristics table for maximum capacitor limits.

The required capacitance above the minimum will be determined by actual transient deviation requirements. See

the TurboTrans Technology application section within this document for specific capacitance selection.

When selecting output capacitors, the main considerations are capacitor type, temperature stability, and ESR.

When using the TurboTrans feature, the capacitance x ESR product should also be considered (see the

following section).

Ceramic output capacitors added for high-frequency bypassing should be located as close as possible to the

load to be effective. Ceramic capacitor values below 10

µF should not be included when calculating the total

output capacitance value.

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.

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

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

using TurboTrans, the capacitor's capacitance (in

µF) × ESR (in mΩ) product determines its capacitor type; Type

A, B, or C. These three types are defined as follows:

Type A = (100

≤ capacitance × ESR ≤ 1000) (e.g. ceramic)

Type B = (1000 < capacitance

× ESR ≤ 5000) (e.g. polymer-tantalum)

Type C = (5000 < capacitance

× ESR ≤ 10,000) (e.g. OS-CON)

When using more than one type of output capacitor, select the capacitor type that makes up the majority of your

total output capacitance. When calculating the C

× ESR product, use the maximum ESR value from the

capacitor manufacturer's data sheet.

Working Examples:

A capacitor with a capacitance of 330

µF and an ESR of 5 mΩ, has a C × ESR product of 1650 µF x mΩ (330 ×

5). This is a Type B capacitor. A capacitor with a capacitance of 1000

µF and an ESR of 8 mΩ, has a C × ESR

product of 8000

µF x mΩ (1000 × 8). This is a Type C capacitor.

See the TurboTrans Technology application section within this document for specific capacitance selection.

Table 3 includes a preferred list of capacitors by type and vendor. See the Output Bus / TurboTrans column.

If the TurboTrans feature is not used, minimum ESR and maximum capacitor limits must be followed. System

stability may be effected and increased output capacitance may be required without TurboTrans.

When using the PTH08T260W without the TurboTrans feature, observe the minimum ESR of the entire output

capacitor bank. The minimum ESR limit of the output capacitor bank is 7 m

Ω. A list of preferred low-ESR type

capacitors, are identified in Table 3. Large amounts of capacitance may reduce system stability when not using

the TurboTrans feature.

When using the PTH08T261W without the TurboTrans feature, the maximum amount of capacitance is tbd

µF of

ceramic type. Large amounts of capacitance may reduce system stability.

Using the TurboTrans feature improves system stability, improves transient response, and reduces the

amount of output capacitance required to meet system transient design requirements.

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