PTH08T240W Datasheet, PDF (8/30 Pages) Texas Instruments – 10-A, 4.5-V to 14-V INPUT, NON-ISOLATED, WIDE-OUTPUT, ADJUSTABLE POWER MODULE WITH TURBOTRANS™

PTH08T240W
SLTS264A – NOVEMBER 2005 – REVISED MARCH 2006
APPLICATION INFORMATION
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CAPACITOR RECOMMENDATIONS FOR THE PTH08T240W POWER MODULE
Input Capacitor (Required)
The required input capacitance is 220-µF of electrolytic type. When V_O > 3V , the 220 µF electrolytic capacitor
must be rated for 700 mArms ripple current capability. For V_O ≤ 3 V, the ripple current rating must be at least 450
mArms. The size, type and value of input capacitor is determined by the converter’s transient performance
capability. 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 applications, or wherever the input source performance is degraded, 470 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 mΩ of equivalent series resistance (ESR), and temperature are the
main considerations when selecting input capacitors. The ripple current reflected from the input of the
PTH08T240W module is moderate to low. Therefore any good quality, computer-grade electrolytic capacitor will
have 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.
TurboTrans Output Capacitor
The PTH08T240W requires a minimum output capacitance of 220 µF. The required capacitance above 220 µF
will be 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 330 µF and 5 mΩ ESR, has a C × ESR product of
1650 µFxmΩ (330 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.
Non-TurboTrans Output Capacitor
The PTH08T240W requires a minimum output capacitance of 220 µF. Non-TurboTrans applications must
observe minimum output capacitance ESR limits.
A combination of 200 µF of ceramic capacitors plus low ESR (15 mΩ 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 mΩ 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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