LED driver suits medium-size LCDs

A high-voltage CMOS output stage in the device allows five LED strings to be accurately biased and regulated from a low voltage input supply while still delivering efficiency levels of up to 87%.

Catalyst Semiconductor has expanded its line of high-power LED drivers with a new device optimised for the mid-size LCD panel market.

The new CAT4139 boost convertor provides a switch current up to 750mA and drives LED strings up to 22V, making it an suitable choice for digital photo frames and other backlighting applications where high LED counts are emerging.

Many high-voltage boost convertors 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 suitable 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%.

The CAT4139 follows Catalyst's CAT4240 high-power boost convertor 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.

Back to top