Catalyst Semiconductor has introduced LED drivers with a new device optimised for the 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.
The CAT4139 uses a fixed frequency (1MHz) switching architecture making it suitable for low noise applications, eliminating disadvantages sich as unwanted harmonics associated with systems that use imple variable-frequency switching schemes. A high voltage CMOS output stage in the device allows 5 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%. 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 over-voltage 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 include switch current limit 750mA; drives high voltage LED strings up to 22V; 1MHz fixed-frequency, low-noise operation; fully protected; and 5-lead TSOT23 (1mm max height) packaging.
Samples are available now. Projected lead-time for production quantities is currently 6 to 8 weeks ARO.
