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FAN5307MP15X Scheda tecnica(PDF) 9 Page - Fairchild Semiconductor |
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FAN5307MP15X Scheda tecnica(HTML) 9 Page - Fairchild Semiconductor |
9 / 13 page 9 www.fairchildsemi.com FAN5307 Rev. 1.0.4 Application Information Adjustable Output Voltage Version The output voltage for the adjustable version is set by the external resistor divider, as shown below: and is calculated as: To reduce noise sensitivity, R1 + R2 should not exceed 1M Ω. Inductor Selection The inductor parameters directly related to device perfor- mances are saturation current and dc resistance. The FAN5307 operates with a typical inductor value of 10µH. The lower the dc resistance, the higher the efficiency. For saturation current, the inductor should be rated higher than the maximum load current plus half of the inductor ripple current that is calculated as follows: where: f = Switching Frequency L = Inductor Value ∆I L = Inductor Ripple Current Input Capacitor Selection For best performances, a low ESR input capacitor is required. A ceramic capacitor of at least 4.7µF, placed as close to the input pin of the device is recommended. Output Capacitor Selection The FAN5307’s switching frequency of 1MHz allows the use of a low ESR ceramic capacitor with a value of 10µF to 22µF. This provides low output voltage ripple. In power save mode the output voltage ripple is independent of the output capacitor value and the ripple is determined by the internal comparator thresholds. The typical output voltage ripple at light load is 1% of the nominal output voltage. PCB Layout Recommendations T he inherently high peak currents and switching fre- quency of the power supplies require a careful PCB lay- out design. Therefore, use wide traces for the high current path and place the input capacitor, the inductor, and the output capacitor as close as possible to the inte- grated circuit terminals. For the adjustable version the resistor divider should be routed away from the inductor to avoid electromagnetic interference. The 6-lead MLP version of the FAN5307 separates the high current ground from the reference ground, therefore it is more tolerant to the PCB layout design and shows better performance. Inductor Value Vendor Part Number Perfor- mance 10µH Sumida CDRH5D28-100 High Efficiency CDRH5D18-100 CDRH4D28-100 Murata LQH66SN100M01L 6.8µH Sumida CDRH3D16-6R8 Smallest Solution 10µH CDRH4D18-100 CR32-100 CR43-100 Murata LQH4C100K04 Table 1: Recommended Inductors 100k Ω V OUT 0.5V 1 R 1 R 2 ------- + × = ∆I L V OUT 1V OUT VIN ⁄ () – Lf × ------------------------------------------ × = Capacitor Value Vendor Part Number 4.7µF Taiyo Yuden JMK212BY475MG 10µF JMK212BJ106MG JMK316BJ106KL TDK C12012X5ROJ106K C3216X5ROJ106M 22µF Murata GRM32DR60J226K Table 2: Recommended Capacitors |
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