LM3570 Datasheet | National Semiconductor

Description The LM3570 device provides a plete 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 chargepump 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 RSET resistor. The device supplies up to 80m A of total load current to acmodate any bination of up to three white LEDs, and additional current from VOUT. The switching frequency is set at 500k Hz. (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 without shutting down the regulated output voltage. Features n 2.7V to 5.5V Input Voltage n Regulated Output Voltage (VOUT = 4.35V) n Regulated IDx 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 80m A 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 500k Hz 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 Li Ion battery-operated equipment including PDAs, hand-held PCs and cellular phones Typical Application...