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PTH04T240F Datasheet(PDF) 11 Page - Texas Instruments |
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PTH04T240F Datasheet(HTML) 11 Page - Texas Instruments |
11 / 34 page CAPACITOR RECOMMENDATIONS FOR THE PTH04T240/241W POWER MODULE Capacitor Technologies Input Capacitor (Required) Input Capacitor Information PTH04T240F www.ti.com............................................................................................................................................................................................ SLTS293 – DECEMBER 2008 Electrolytic Capacitors When using electrolytic capacitors, 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 required. Ceramic Capacitors Above 150 kHz the performance of aluminum electrolytic capacitors is less effective. Multilayer ceramic capacitors have very low ESR and a resonant frequency higher than the bandwidth of the regulator. They can be used to reduce the reflected ripple current at the input as well as improve the transient response of the output. Tantalum, Polymer-Tantalum Capacitors Tantalum type capacitors may only used on the output bus, and are recommended for applications where the ambient operating temperature is less than 0°C. The AVX TPS series and Kemet capacitor series are suggested over many other tantalum types due to their lower ESR, higher rated surge, power dissipation, and ripple current capability. Tantalum capacitors that have no stated ESR or surge current rating are not recommended for power applications. The PTH04T240F requires a minimum input capacitance of 220 µF. The ripple current rating of the input capacitor must be at least 500mArms. An additional 22- µF, X5R/X7R ceramic capacitor is recommended to reduce the RMS ripple current. The size and value of the input capacitor is determined by the converter 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. Ceramic capacitors should be located as close as possible to the module's input pins, within 0.5 inch (1,3 cm). Adding ceramic capacitance is necessary to reduce the high-frequency ripple voltage at the module input. This reduces the magnitude of the ripple current through the electroytic capacitor, as well as the amount of ripple current reflected back to the input source. Additional ceramic capacitors can be added to further reduce the RMS ripple current requirement for the electrolytic capacitor. Increasing the minimum input capacitance to 680µF is recommended for high-performance applications, or wherever the input source performance is degraded. The main considerations when selecting input capacitors are the RMS ripple current rating, temperature stability, and less than 100 m Ω of equivalent series resistance (ESR). 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. Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 11 Product Folder Link(s): PTH04T240F |
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