Datasheet

CAPACITOR RECOMMENDATIONS FOR THE PTH05T210W POWER MODULE
Input Capacitor (Required)
TurboTrans Output Capacitor
Non-TurboTrans Output Capacitor
PTH05T210W
SLTS263I – AUGUST 2007 – REVISED MARCH 2009 ...................................................................................................................................................... www.ti.com
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 µ F, 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 µ F 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 µ F. The required capacitance above 470 µ F 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 ( µ F) × ESR (m Ω ) product of ≤ 10,000m Ω × µ F are required.
Working Example:
A bank of 6 identical capacitors, each with a capacitance of 680 µ F and 5m Ω ESR, has a C × ESR product of
3400 µ Fxm Ω (680 µ F × 5m Ω ).
Using TurboTrans in conjunction with the high quality capacitors (capacitance ( µ F) × ESR (m Ω )) reduces the
overall capacitance requirement while meeting the minimum transient amplitude level.
Table 3 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 µ F. Non-TurboTrans applications must observe
minimum output capacitance ESR limits.
A combination of 200 µ F of ceramic capacitors plus low ESR (15m Ω to 30m Ω ) 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 3m Ω to 5m Ω . (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.
When using a combination of one or more non-ceramic capacitors, the calculated equivalent ESR should be no
lower than 2m Ω (4m Ω when calculating using the manufacturer ’ s maximum ESR values). A list of preferred
low-ESR type capacitors, are identified in Table 3 .
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