Torex Step-Up DC-DC Converter Is Ideal Backlight Driver Solution For Hand-Helds

New from Torex Semiconductor is the XC9133 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, mobile phones and digital cameras.

The XC9133 device 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. Alternatively, using an input of 3.2V or more, the new 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 new XC9133 is a highly integrated device combining reference voltage, ramp wave circuit, error amplifier, PWM comparator, phase compensation circuit, current limit circuit and N-channel MOSFET driver (RDS-ON of 2.4Ω) in a single package. All that is required to achieve an ultra compact, low profile solution for driving white LEDs is a chip coil and a tiny output capacitor of 0.22μF.

A switching frequency of 1.0MHz and the device’s low feedback reference voltage, which ensures that RLED losses are minimal, combine to make the XC9133 a highly efficient solution. For example, when driving three LEDs in series, VIN = 3.6V and ILED = 20mA, efficiency is 85%.

The XC9133 has an additional fault detection circuit, the Lx over voltage limit circuit, so that if the LEDs are opened or damaged, the voltage feedback (FB) pin is pulled down and any excessive increase in output voltage is prevented.