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Backlight driver solution for handhelds

The XC9133 series from Torex Semiconductor is a fixed frequency, constant current, step-up dc-dc converter suitable for driving the white leds used in lcd backlighting applications.

This includes 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. From a 2.5V input, four white leds can be driven in series. Alternatively, using an input of 3.2V or more, 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 new XC9133 is an integrated device combining reference voltage, ramp wave circuit, error amplifier, pwm comparator, phase compensation circuit, current limit circuit and N-channel MOSFET driver.
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 pin is pulled down and any excessive increase in output voltage is prevented.

Author
Chris Shaw

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