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MP1523DT Datasheet(PDF) 5 Page - Monolithic Power Systems |
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MP1523DT Datasheet(HTML) 5 Page - Monolithic Power Systems |
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5 / 7 page  MP1523 – PRECISION 6-LAMP WHITE LED DRIVER INITIAL RELEASE 07/04, Rev. 1.6 www.MonolithicPower.com 5 APPLICATIONS INFORMATION Setting the LED current The LED current is set by the sense resistor (R2) at FB. The LED current can be calculated as: 2 R V I FB LED = Where VFB is 400mV. The LED current is set to 20mA if R2 = 20Ω. Capacitor Selection A 1µF to 10µF ceramic input capacitor (C1) and a 0.47µF to 1µF ceramic output capacitor (C2) are recommended for most applications. A capacitor (typically 1nF) in parallel with the LED string improves stability, input and output ripple especially when large inductance values (10µH or above) are used. For best stability over a wide temperature range, use capacitors with an X5R or X7R dielectric. Inductor selection The MP1523 has a 450mA inductor current limit and can drive up to 6 LEDs at 20mA. Inductance values (L1) from 4.7µH to 47µH work satisfactorily. Larger values provide the best efficiency while small inductor values allow the smallest inductor size. To prevent saturation, use an inductor with a saturation current rating that matches the device current limit. Diode selection The MP1523’s high switching frequency demands a high-speed rectifier (D1) for optimum efficiency. A schottky diode is recommended due to its fast recovery time and low forward voltage drop. Ensure the diode’s average and peak current ratings exceed the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed the output voltage. Layout Careful PC board layout is required due to fast- switching. All components must be placed as close to the IC as possible. Keep the path between inductor L1, diode D1, and output capacitor C2 extremely short for minimal noise and ringing. The feedback components such as sense resistor R2 must be kept close to the FB pin to prevent noise injection on the FB pin trace. The ground return of C1 and C2 should be tied close to the GND pin. See the MP1523 demo board layout for reference. |
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Similar Description - MP1523DT |
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