STMicroelectronics and Semtech introduce LED backlight drivers

STMicroelectronics targets handheld mobile devices while Semtech targets tablets and small notebook PCs.

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STMicroelectronics introduced the STLA02 driver that can power six LEDs for backlighting in applications such as smartphones, portable gaming devices, and GPS receivers. Semtech has announced the SC5010 phase-shifted LED backlight driver for notebook and tablet applications with displays as thin as 4 mm.

ST's STLA02 LED driver

The STMicroelectronics STLA02 IC can operate from battery supply voltages ranging from 2.5V to 18V and deliver 20 mA to the 6-LED string. The wide input range allows the device to operate from varied battery types including single lithium cells.

As the nearby figure shows, the IC requires a minimum number of external components. The IC integrates current-sensing capabilities via a feedback pin that relies simply on a feedback resistor on the high side of the LED stack. The low side is connected directly to ground. The driver includes over-voltage, and over-temperature protection.

The STLA02 uses a step-up boost DC-DC converter topology to support a 27V supply to the LED stack. The switching design operates at 2.3 MHz. And integrated pulse-width-modulation (PWM) dimming capability supports a 300:1 dimming range.

Semtech driver targets notebooks and tablets

Semtech, meanwhile, is targeting larger devices with its new driver that can drive 8 strings of LEDs with up to 14 LEDs per string at 30 mA. The company says that its driver can work with smaller inductors than competitive products enabling thinner displays.

The boost-based driver topology utilizes what the company calls a "sophisticated control loop architecture" to allow efficient operations with 2.2 μH inductors that are only 1-mm high. Athar Zaidi, director of marketing in Semtech's Power Management Group, said, " Now, for the first time, ultrabook PC manufacturers can place efficient, phase-shifted LED drivers where they prefer them - next to the display, which, until now, has been a roadblock for ultrabook and other very small form factor PCs."

The driver also utilizes a phase shifted approach to driving different LED channels so that not all channels are powered on at any given time. There is a detailed article on the technique in the October 2011 issue of LEDs Magazine on page 77.

Semtech says that the phase-shifted architecture reduces input and output capacitance issues resulting in lower noise and electromagnetic interference (EMI), thereby eliminating the need for noise filtering components. Zaidi said, "The SC5010 offers a superior phase-shifted LED driver approach that significantly reduces the tradeoffs between inductor size and display efficiency."

The driver supports PWM-based dimming over a 5000:1 range. It includes over-voltage, over-temperature, and under-voltage protection. Efficiency is up to 92% depending on the design and switching frequency can vary between 200 kHz and 2.2 MHz.

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