The FAN5640 is designed to illuminate one or two strings of keypad LEDs with constant high-side current sources. The device can drive up to four white LEDs in series at a maximum current of 25 mA per channel. If the second channel is not needed, the channels can be tied together to boost output current up to 50 mA. An external resistor programs the maximum output current. Dimming can be accomplished by pulse width modulation of the enable pin or the input supply rail.