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PTH08T240W Datasheet(PDF) 8 Page - Texas Instruments |
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PTH08T240W Datasheet(HTML) 8 Page - Texas Instruments |
8 / 30 page www.ti.com APPLICATION INFORMATION CAPACITOR RECOMMENDATIONS FOR THE PTH08T240W POWER MODULE Input Capacitor (Required) TurboTrans Output Capacitor Non-TurboTrans Output Capacitor PTH08T240W SLTS264A–NOVEMBER 2005–REVISED MARCH 2006 The required input capacitance is 220-µF of electrolytic type. When VO >3V,the220 µF electrolytic capacitor must be rated for 700 mArms ripple current capability. For VO ≤ 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. 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. 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. 8 Submit Documentation Feedback |
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