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LM3354MMX-4.1 データシート(PDF) 11 Page - National Semiconductor (TI) |
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LM3354MMX-4.1 データシート(HTML) 11 Page - National Semiconductor (TI) |
11 / 12 page Driving Light Emitting Diodes The LM3354 can be used to drive LED’s of nearly any color. The 4.1V option is ideal for driving the White LED’s required for the backlight of small color displays. Figure 4 shows the circuit used to power White LED’s. The LED current is set by the resistors R B by using the equation ILED = (4.1V − VF)/RB where V F is the typical forward voltage drop of the LED used. The brightness of the diodes may be controlled using the shutdown pin. A PWM signal on the shutdown pin may be used to adjust the brightness by varying the duty cycle. A signal between 60Hz and 200Hz may be used for best linearity. In this case the equivalent LED current is approxi- mately equal to the maximum current multiplied by the duty cycle. Using frequencies above 200Hz may cause less linear results as the charge and discharge time of the output capacitor becomes more significant. Layout Considerations Due to the 1 MHz typical switching frequency of the LM3354, careful board layout is a must. It is important to place the capacitors as close to the IC as possible and to keep the traces between the capacitors and the IC short and direct. Use of a ground plane is recommended. Figure 5 shows a typical layout as used in the LM3354 evaluation board. DS200188-16 FIGURE 5. Typical Layout, Top View (magnification 1.5X) www.national.com 11 |
同様の部品番号 - LM3354MMX-4.1 |
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同様の説明 - LM3354MMX-4.1 |
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