Datenblatt-Suchmaschine für elektronische Bauteile |
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FAN4855MTCX Datenblatt(PDF) 10 Page - Fairchild Semiconductor |
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FAN4855MTCX Datenblatt(HTML) 10 Page - Fairchild Semiconductor |
10 / 12 page 10 www.fairchildsemi.com FAN4855 Rev. 1.0.1 Layout and Grounding Considerations Careful design of printed circuit board is recommended since high frequency switching and high peak currents are present in DC/DC converters applications. A general rule is to place the converter circuitry well away from any sensitive analog components. The printed circuit board layout should be based on some simple rules to minimize EMI and to ensure good regulation performances: 1. Place the IC, inductor, input and output capacitor as close together as possible. 2. Keep the output capacitor as close to the FAN4855 as possible with very short traces to VOUT and GND pins. Typically it should be within 0.25 inches or 6 mm. 3. Keep the traces for the power components wide, typically > 50 mils or 1.25 mm. 4. Place the external networks for LBI and FB close to FAN4855, but away from the power components as far as possible to prevent voltage transient from cou- pling into sensitive nodes. 5. On multilayer boards use component side copper for grounding around the IC and connect back to a quiet ground plane using vias. The ground planes act as electromagnetic shields for some of the RF energy radiated. 6. The connection of the GND pin of the IC (pin 8) to the overall grounding system should be directly to the bottom of the output filter capacitor. A star grounding system radiating from where the power enters the PCB, is a recommended practice. Application Example The FAN4855 can be used as a constant current source to drive white LEDs like QTLP670C-IW. As shown in the diagram below, the current is maintained constant over a wide range of input voltages. L = 10µH D1 FAN4855 1 2 3 4 8 7 6 5 D2 Cout 10µF Cin 10µF + + + D3 D4 62 Ω 62 Ω 62 Ω 62 Ω 20 Input Voltage (V) 19.8 19.6 19.4 19.2 19 18.8 18.6 18.4 18.2 18 012 3 4 5 |
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