Catalyst Semiconductor Inc. has expanded its line of high-power LED drives with a new device optimized for the rapidly growing mid-size LCD panel market. The new CAT4139 boost converter provides a switch current up to 750mA and drives LED strings up to 22V, making it a suitable choice for digital photo frames and other backlighting applications where high LED counts (up to 40 LEDs) are emerging.

Many high-voltage boost converters typically use a simple variable-frequency switching scheme. This approach results in a wide range of unwanted harmonics, which are not easy to filter or eliminate. The CAT4139 uses a fixed frequency (1MHz) switching architecture making it ideal for low noise applications. A high voltage CMOS output stage in the device allows five LED strings (up to 22V) to be accurately biased and regulated from a low voltage input supply while still delivering efficiency levels of up to 87 percent. The CAT4139 follows Catalyst's CAT4240 high-power boost converter introduced earlier this year, which drives 10 LED strings up to 38V each.

To eliminate excessive in-rush currents, which can occur during initial power-up, the CAT4139 offers an integrated soft-start control. In the event of an open-LED fault condition, an internal overvoltage protection circuit will place the device into a low-power operating mode restricting the output voltage to safe levels without the need for external circuitry. Both of these features are fully integrated, eliminating the need for external components and the associated cost and board space overhead.

Designers have a choice of controlling LED dimming in the CAT4139 using a DC voltage, logic signal, or pulse width modulation (PWM) signal.

Product Features

Housed in 5-lead TSOT23 (1mm max height), the CAT4139 LED driver is priced at 64 cents each in 10,000 piece quantities. Samples are available now. Projected lead-time for production quantities is currently six to eight weeks ARO.