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FAN2011 Folha de dados(PDF) 8 Page - Fairchild Semiconductor |
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FAN2011 Folha de dados(HTML) 8 Page - Fairchild Semiconductor |
8 / 10 page 8 www.fairchildsemi.com FAN2011/FAN2012 Rev. 1.0.4 Applications Information Setting the Output Voltage The internal reference is 0.8V. The output is divided down by a voltage divider, R1 and R2 to the FB pin. The output voltage is: According to this equation, and assuming desired output voltage of 1.5096V, and given R2 = 10K Ω, the calculated value of R1 is 8.87K Ω. Inductor Selection The inductor parameters directly related to device perfor- mances 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 calculated as follows: where: ∆I L = 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 recom- mended. The output capacitor determines the output rip- ple and the transient response. Table 2. Recommended Capacitors PCB Layout Recommendations The inherently high peak currents and switching fre- quency 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 out- put capacitor as close as possible to the integrated cir- cuit terminals. To minimize voltage stress to the device resulting from ever-present switching 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 switch- ing 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 recom- mended 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 3.3µH Coiltronics SD-3R3-R Capacitor Value Vendor Part Number 10µF Taiyo Yuden JMK212BJ106MG JMK316BJ106KL TDK C2012X5ROJ106K C3216X5ROJ106M Murata GRM32ER61C106K V OUT V REF 1 R 1 R 2 ------- + = ∆I L V OUT 1V OUT V IN ⁄ () – Lf × ------------------------------------------ × = |
Nº de peça semelhante - FAN2011 |
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Descrição semelhante - FAN2011 |
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