Electroluminescent Lamp Driver for Cellular Phones

Sipex CorporationP4438 is an ultra-quiet electroluminescent lamp (EL) driver designed to power EL lamps for backlighting liquid crystal displays and keypads in cellular phones and other wireless communication devices.

The driver features clipped-sinusoid waveform, with gradual rising and falling edges, to obtain the lowest acoustic noise. This output waveform, combined with constant current to the lamp and low-frequency operation, also minimizes electromagnetic interference and stress on the lamp to extend lamp lifetime.

The device operates from a 2.7V to 3.3V supply and is designed to drive cell-phone-sized lamps from 1 to 3 square inches. One external resistor is used to set the internal oscillator frequency, and one inductor is required to generate the high-voltage AC output to drive an EL lamp. The device operates from a +3.0V battery source and has a standby mode that draws less than 1uA, making it ideal for low-power cellular applications. It also uses low-profile 470uH coils (<2mm height) for applications requiring thin form factors. Current sources and precision-controlled timing of the SP4438 switched H-bridge network are designed to reduce EMI emissions, extend EL lamp life, and reduce the overall power dissipation of the device.

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