New from Torex Semiconductor is the XC9116 series, a fixed frequency, constant current, step-up DC-DC converter that is ideal for driving the white LEDs used in LCD backlighting applications in a wide range of hand-held designs, such as PDAs, cellular phones and digital cameras. Backlighting with white LEDs is by far the simplest way of producing a 'brighter' LCD in handheld devices.
The XC9116 has an input voltage range of 2.5 to 6.0V and can deliver output voltages up to 17.5V. Thus from a 2.5V input, four white LEDs can be driven in series. Alternative]y, using a 3.2V input, the DC-DC converter is able to drive a network of two parallel banks of three LEDs. The luminance of the LEDs is controlled by varying the duty cycle of a 10kHz PWM signal applied to the device's CE pin. The XC9116 is a highly integrated device combining reference voltage, ramp wave circuit, error amplifier, PWM comparator, phase compensation circuit, overvoltage limit, current limit and N-channel MOS driver transistor (Rds-on of 2 Ohm) in a single package. All that is additionally required to achieve an ultra compact, low profile solution for driving white LEDs is a chip coil and a tiny output capacitor of 0.22F. Torex Semiconductor Europe Ltd, Coalville, Leicestershire LE67 4JP, UK. www.torex.co.jp