SAN JOSE, Calif. IMP Inc. has introduced the IMP528 electroluminescent (EL) lamp-driver IC, featuring a 220-V peak-to-peak ac drive signal derived from dc or battery sources as low as 2 V. It allows pager and cellular-phone display screens to be backlit by electroluminescent lamps without bulky transformers.
EL-lamp backlighting apps include keyless-entry systems; audio/video-equipment remote controllers; PDA keyboards and displays; watches; LCD displays in cell phones, pagers and handheld global positioning systems (GPS); face illumination for instrumentation; assistance lighting for buildings and decorative lighting for sign displays and merchandising displays.
"The IMP528 targets applications where maximum display brightness is needed over a wide operating-voltage range," said IMP marketing vice president Barry Wiley. It incorporates four EL lamp-driving functions on-chip: the boost switch-mode power supply, high-frequency oscillator, high-voltage H-bridge lamp driver and low-frequency oscillator.
External components required include an inductor, a diode, a capacitor and two resistors for independent adjustment of boost converter frequency and EL lamp drive frequency. Adjustable lamp drive frequency allows control over lamp color and power dissipation. No external resistor is needed in series with the EL lamp for protection.
The 220-V drive signal is derived from a 2-V to 6.5-V dc input voltage. For EL lamps commonly used in battery-powered handheld communication and computing devices, the IMP528 output will be held constant by an internal regulator, which is said to maximize brightness over the full battery life. The IMP528 can be disabled when it's not needed to drive the EL backlight, reducing the current to 200 nA.
The IMP528, available in 8-pin MicroSO and SO packages (the MicroSO package uses 50 percent less printed-circuit-board mounting area than the SO package), is priced at $1.09 each in 1,000 piece quantities.
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EETInfo No. 622