Datasheet

Output Capacitor (Required)
Output Capacitor Information
TurboTrans Output Capacitance
Non-TurboTrans Output Capacitance
PTH04T240W , PTH04T241W
www.ti.com ...................................................................................................................................................... SLTS276D – OCTOBER 2006 – REVISED JULY 2009
The PTH04T241W requires a minimum output capacitance of 300 µ F of ceramic type.
The PTH04T240W requires a minimum output capacitance of 220 µ F of aluminum, polymer-aluminum, tantulum,
or polymer-tantalum type.
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 µ F 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 ( µ F) × ESR (m Ω ) 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 datasheet.
The PTH04T241W should be used when only Type A (ceramic) capacitors are used on the output.
Working Examples:
A capacitor with a capacitance of 330 µ F and an ESR of 5m Ω , has a C × ESR product of 1650 µ Fxm Ω (330 µ F ×
5m Ω ). This is a Type B capacitor. A capacitor with a capacitance of 1000 µ F and an ESR of 8m Ω , has a C × ESR
product of 8000 µ Fxm Ω (1000 µ F × 8m Ω ). 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 PTH04T240W, observe the minimum ESR of the entire output capacitor bank. The minimum
ESR limit of the output capacitor bank is 7m Ω . A list of preferred low-ESR type capacitors, are identified in
Table 3 .
When using the PTH04T241W without the TurboTrans feature, the maximum amount of capacitance is 3000 µ F
of ceramic type. Large amounts of capacitance may reduce system stability.
Utilizing 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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