Step-up convertors power LED backlights

Devices include on-chip MOSFETs to reduce part count, and operate up to 1MHz to minimise the need for filtering components.

STMicroelectronics has developed three monolithic step-up convertors for LED backlights and lighting, providing 30 or 85mA current sources for six rows of up to 10 white LEDs.

The LED7706, LED7707 and mobile-optimised PM6600 include on-chip MOSFETs to reduce part count, and operate up to 1MHz to minimise the need for filtering components.

The 30mA LED7706 and 85mA LED7707, with an output voltage of 36V, enable a single-chip solution for LCD panels as large as 17in.

An external synchronisation pin allows connection of extra devices for larger screen sizes.

The LED7707's 85mA output also satisfies stand-alone LED lighting applications.

The third device introduced, the PM6600, joins ST's PM66xx family, which provides a complete notebook and ultramobile PC power-management solution.

Six 36V constant-current channels of 30mA serve applications up to large-notebook size.

Like the other two devices, the PM600 features a synchronisation pin to operate larger displays.

In addition, the PM6600 implements extensive fault-management to control backlight operation if the display sustains damage to the flexible cable or to groups of LEDs.

Detection of intermittent faults, shorted LEDs, single or multiple open rows, or combinations of defects, allow fault-tolerant operation in the field and assist with maintenance and repair.

The PM6600 accepts input voltages from 4.5 to 28V.

All three devices include power-saving modes to optimise efficiency under light-load conditions, as well as PWM dimming down to 1% duty cycle.

Each device is stable with a ceramic output capacitor to reduce bill-of-materials costs.

There is also built-in protection against thermal overload, output over-voltage and MOSFET over-current.

The 24-pin VFQFPN package measuring 4 x 4mm delivers a low-footprint solution.

A soft-start function is also featured, to maximise the lifetime of the backlight.

The LED7706 and LED7707 are available immediately at US $1.80 and $1.90, respectively, for 1000 pieces.

The PM6600 is also in full production, and is available for $1.80 each in quantities of 1000.

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