The CAT4137 is a DC/DC step-up converter that delivers a regulated output current. Operation at a constant switching frequency of 1 MHz allows the device to be used with small value external ceramic capacitors and inductor. The device drives a string of white LEDs connected in series and provides the regulated current to control the LEDs with inherent uniform brightness and matching. An external resistor R1 sets the output current and allows up to 30 mA current to be supported over a wide range of input supply voltages from 2.2 V to 5.5 V, making the device ideal for battery-powered applications. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown control pin allows the device to be placed in power-down mode with "zero" quiescent current.