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 RSET 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 VOUT. 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 without shutting down the regulated output voltage.