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LM3570SD Datasheet(PDF) 1 Page - National Semiconductor (TI) |
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LM3570SD Datasheet(HTML) 1 Page - National Semiconductor (TI) |
1 / 13 page LM3570 Low Noise White LED Driver System General Description The LM3570 device provides a complete LED driver solution for wireless handsets and other portable devices using a display and keypad. With three constant current sources, up to three white LEDs can be used for display lighting with excellent current matching (0.3% typ.). The regulated 4.35V output voltage is perfect for driving auxiliary keypad LEDs in voltage mode. The LM3570 utilizes a high efficiency 3/2 CMOS charge- pump with a pre-regulation loop that minimizes conducted noise on the input. It accepts an input voltage range from 2.7V to 5.5V and maintains a constant current determined by the current through an external R SET resistor. The device supplies up to 80mA of total load current to accommodate any combination of up to three white LEDs, and additional current from V OUT. The switching frequency is set at 500kHz. (typ.) to keep the conducted noise spectrum away from sensitive frequencies within portable RF devices. By applying a pulse width modulated (PWM) signal to the PWM pin, the user has the ability to independently control the brightness of the regulated current source outputs with- out shutting down the regulated output voltage. Features n 2.7V to 5.5V Input Voltage n Regulated Output Voltage (V OUT = 4.35V) n Regulated I Dx with ±0.3% matching between constant current outputs n High Efficiency 3/2 Boost function n Drives one, two, or three white LEDs with no bias resistor losses n Drives auxiliary keypad LEDS in voltage mode n Up to 80mA total output current n Active-High Enable n Active-High PWM Control Pin for independent control of current sources n Very small solution size n 1µA(max) shutdown current n 500kHz switching frequency (typ.) n Linear regulation generates predictable noise spectrum n LLP-14 package: 4.0mm X 3.0mm X 0.8mm Applications n Portable devices using white or blue LEDs with display and backlight or frontlight n 1-Cell LiIon battery-operated equipment including PDAs, hand-held PCs and cellular phones Typical Application Circuit 20085021 July 2004 © 2004 National Semiconductor Corporation DS200850 www.national.com |
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