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FAN2013 数据表(PDF) 7 Page - Fairchild Semiconductor |
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FAN2013 数据表(HTML) 7 Page - Fairchild Semiconductor |
7 / 9 page © 2006 Fairchild Semiconductor Corporation www.fairchildsemi.com FAN2013 Rev. 1.0.3 7 Applications Information Setting the Output Voltage The internal voltage reference is 0.8V. The output is divided down by a voltage divider, R1 and R2 to the FB pin. The output voltage is: V OUT V REF 1 R 1 R 2 ------ + = (2) According to this equation, assuming desired output voltage of 1.2V, and given R2 = 10K Ω as the recommended resistance for any output voltage setting, the calculated value of R1 is 5K Ω. Inductor Selection The inductor parameters directly related to device performance are saturation current and DC resistance. The FAN2013 operates with a typical inductor value of 2.2µH. 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 by: ∆IL VOUT 1 V OU T V IN ⁄ () – Lf × ------------------------------------------- × = (3) where: ΔIL = Inductor Ripple Current f = Switching Frequency L = Inductor Value Recommended inductors are listed in Table1. Table 1. Recommended Inductors Inductor Value Vendor Part Number 2.2µH Coiltronics SD25 2R2 2.2µH Murata LQH66SSN2R2M03 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 as possible is recommended. The output capacitor determines the output ripple and the transient response. A minimum of 20µF output capacitor is required for the FAN2013 to operate in stable conditions. Table 2. Recommended Capacitors Capacitor Value Vendor Part Number JMK212BJ106MG Taiyo Yuden JMK316BJ106KL C2012X5ROJ106K TDK C3216X5ROJ106M 10µF Murata GRM32ER61C106K PCB Layout Recommendations The inherently high peak currents and switching frequency of power supplies require a careful PCB layout design. For best results, 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. To minimize voltage stress to the device resulting from ever-present switching spikes, use an input bypass capacitor with low ESR. 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 11. Figure 11. Recommended PCB Layout |
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类似说明 - FAN2013 |
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