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PTH03010YAST Datasheet(PDF) 10 Page - Texas Instruments |
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PTH03010YAST Datasheet(HTML) 10 Page - Texas Instruments |
10 / 18 page www.ti.com CAPACITOR RECOMMENDATIONS FOR THE PTH12010Y DDR POWER MODULES INPUT CAPACITOR OUTPUT CAPACITORS CERAMIC CAPACITORS TANTALUM CAPACITORS CAPACITOR TABLE PTH03010Y PTH05010Y PTH12010Y SLTS223A–MARCH 2004–REVISED OCTOBER 2005 (12-V OPTION) The recommended input capacitance is determined by the 560 µF minimum capacitance and 750 mArms minimum ripple current rating. A 10-µF X5R/X7R ceramic capacitor may also be added to reduce the reflected input ripple current. The ceramic capacitor should be located between the input electrolytic and the module. Ripple current, less than 100 mΩ equivalent series resistance (ESR) and temperature are major considerations when selecting input capacitors. Unlike polymer-tantalum capacitors, regular tantalum capacitors have a recommended minimum voltage rating of 2 × (max dc voltage + ac ripple). This is standard practice to ensure reliability. No tantalum capacitors were found with sufficient voltage rating to meet this requirement. At temperatures below 0°C, the ESR of aluminum electrolytic capacitors increases. For these applications, Os-Con, polymer-tantalum, and polymer-aluminum types should be considered. For applications with load transients (sudden changes in load current), regulator response benefits from external output capacitance. The recommended output capacitance of 940 µF will allow the modue to meet its transieint response specification. (See Electrical Specifications table). For most applications, a high quality computer-grade aluminum electrolytic capacitor is adequate. These capacitors provide decoupling over the frequency range, 2 kHz to 150 kHz, and are suitable for ambient temperatures above 0°C. Below 0°C, tantalum, ceramic or Os-Con type capacitors are recommended. When using one or more nonceramic capacitors, the calculated equivalent ESR should be no lower than 4 mΩ (7 mΩ using the manufacturer’s maximum ESR for a single capacitor). A list of preferred low-ESR type capacitors are identified in Table 2. In addition to electrolytic capacitance, adding a 10-µF to 22-µF X5R/X7R ceramic capacitor to the output reduces the output ripple voltage and improve the regulator’s transient response. The measurement of both the output ripple and transient response is also best achieved across a 10-µF ceramic capacitor. 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. When used on the output, their combined ESR is not critical as long as the total value of ceramic capacitance does not exceed 300 µF. Also, to prevent the formation of local resonances, do not place more than five identical ceramic capacitors in parallel with values of 10 µF or greater. Tantalum type capacitors are most suited for use on the output bus, and are recommended for applications where the ambient operating temperature can be less than 0°C. The AVX TPS, Sprague 593D/594/595 and Kemet T495/T510 capacitor series are suggested over other tantalum types due to their higher rated surge, power dissipation, and ripple current capability. As a caution, many general purpose tantalum capacitors have considerably higher ESR, reduced power dissipation and lower ripple current capability. These capacitors are also less reliable as they have lower power dissipation and surge current ratings. Tantalum capacitors that do not have a stated ESR or surge current rating are not recommended for power applications. When specifying Os-con and polymer tantalum capacitors for the output, the minimum ESR limit are encountered well before the maximum capacitance value is reached. Table 2 identifies the characteristics of capacitors from a number of vendors with acceptable ESR and ripple current (rms) ratings. The recommended number of capacitors required at both the input and output buses is identified for each capacitor type. This is not an extensive capacitor list. Capacitors from other vendors are available with comparable specifications. Those listed are for guidance. The RMS ripple current rating and ESR (at 100 kHz) are critical parameters necessary to insure both optimum regulator performance and long capacitor life. 10 |
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