Boost convertor drives four white LEDs

Edited by the Electronicstalk editorial team Apr 20, 2004

The CAT37 is an inductor-based white LED driver boost convertor designed for colour LCD and keypad backlighting.

Catalyst Semiconductor has expanded its white light emitting diode (LED) product family with the introduction of the CAT37, an inductor-based white LED driver boost convertor.

Designed for colour LCD and keypad backlighting, the CAT37 delivers a regulated output current at a constant switching frequency of 1.2MHz that allows the device to be used with very small value external inductor and ceramic capacitors.

The CAT37 has been optimised to drive up to four white LEDs.

Its power efficiency of over 80% and shutdown current of less than 1uA provide optimal battery run time in handheld applications, while its low 2.5V input voltage operation makes it ideal for use in single cell Li-ion and multicell alkaline/NiMH battery powered devices.

The CAT37 delivers a constant current to series-connected LEDs, ensuring uniform brightness regardless of variations in the LEDs forward voltage drops.

Its high accuracy feedback voltage, regulated at 95mV, ensures high frequency and provides reliable brightness control even when partially dimmed to current levels of 6 to 8mA.

The CAT37 can also safely withstand an open output circuit.

The combination of the CAT37's high efficiency, low noise, and low profile 5-lead SOT23 and TDFN packages make it the ideal LED driver for any handheld application requiring up to four white LEDs for LCD backlighting, such as cellphones and digital cameras.

"Catalyst is focused on the solid state illumination marketplace", said Barry Wiley, Vice President of Analog and Mixed-Signal Marketing and Sales.

"The use of colour LCD screens is an irreversible growing trend in the marketplace, eg according to IC Insights, the use of colour screens in cellphones alone will grow from 160 million units in 2003 to a forecasted 365 million units in 2005".

"Other illumination applications in which Catalyst is an active supplier are digital cameras, where in addition to backlighting, Catalyst also supplies digitally programmable potentiometers (DPP), for contrast control of LCD screens".

"The illumination application is a major future market for Catalyst".

Target applications for white LED drivers include backlighting of LCD displays in PDAs, portable MP3 players, cellular phones, handheld terminals, and digital cameras.

In addition, white LEDs are used for backlighting keypads, camera flash equipment and illumination in automotive and aircraft markets.