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FAN2012 Fiches technique(PDF) 8 Page - Fairchild Semiconductor |
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FAN2012 Fiches technique(HTML) 8 Page - Fairchild Semiconductor |
8 / 10 page 8 www.fairchildsemi.com FAN2011/FAN2012 Rev. 1.0.2 Inductor Selection The inductor parameters directly related to device performances are saturation current and dc resistance. The FAN2011/ FAN2012 operates with a typical inductor value of 3.3µH. 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 calcu- lated as follows: where: ∆IL = Inductor Ripple Current f = Switching Frequency L = Inductor Value Some recommended inductors are suggested in the table below: Table 1: Recommended Inductors Capacitors Selection For best performances, a low ESR input capacitor is required. A ceramic capacitor of at least 10µF, placed as close to the VIN and AGND pins of the device is recommended. The output capacitor determines the output ripple and the transient response. Table 2: Recommended Capacitors PCB Layout Recommendations The inherently high peak currents and switching frequency of power supplies require a careful PCB layout design. Therefore, use wide traces for high current paths and place the input capacitor, the inductor, and the output capacitor as close as possible to the integrated circuit terminals. In order to minimize voltage stress to the device resulting from ever present switch- ing spikes, use an input bypass capacitor with low ESR. Use of an external Schottky diode with its anode connected to SW node and cathode connected to PVIN further reduces switching spikes. Note that the peak amplitude of the switching spikes depends upon the load current; the higher the load current, the higher the switching spikes. The resistor divider that sets the output voltage should be routed away from the inductor to avoid RF coupling. The ground plane at the bottom side of the PCB acts as an electromagnetic shield to reduce EMI. The recommended PCB layout is shown below in Figure 5. Figure 5. Recommended PCB Layout Inductor Value Vendor Part Number 3.3µH Panasonic ELL6PM3R3N 3.3µH Murata LQS66C3R3M04 Capacitor Value Vendor Part Number 10µF Taiyo Yuden JMK212BJ106MG JMK316BJ106KL TDK C2012X5ROJ106K C3216X5ROJ106M Murata GRM32ER61C106K ∆I L V OUT 1V OUT V IN ⁄ () – Lf × ------------------------------------------ × = |
Numéro de pièce similaire - FAN2012 |
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Description similaire - FAN2012 |
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