LED drivers provide ultra-low dimming

A new family of multi-channel LED drivers from Intersil Corp. provides an ultra-low dimming capability that can significantly extend battery life in notebook, netbook, and tablet computers. The highly integrated ISL97671/2/3/4 series reduces undesirable backlight-induced visual artifacts such as flickering, shimmering, and banding that are observed when using conventional LED drivers.

The devices minimize power loss by using a proprietary dynamic headroom control circuit to detect the highest voltage LED string, and then regulate the boost output to the minimum required voltage. The devices drive up to six 40 mA strings of LEDs from a 4.5 to 26 V input. A highly accurate LED current matching circuit achieves a ± 0.7% current matching between LED strings. The ISL97671/2/3/4 series also includes an integrated boost converter to step-up the input voltage to support LED stack voltages up to 45 V.


The drivers maintain dimming linearity even at low LED PWM duty cycles by using an adaptive boost control circuit that regulates the output voltage even when the LEDs are off for most of the PWM cycle. Using this boost architecture, the ISL97671/2/3/4 series responds to very low PWM duty cycles and provides dimming down to just 0.007% of full brightness with a 200 Hz PWM frequency. Dimming may be controlled by direct PWM dimming or by using 8-bit digital dimming via an I2C/SMBus interface.

The devices' phase shift capability can turn LED strings on at a specified phase, reducing peak input current by distributing channel currents within the dimming period. This feature contrasts with conventional multi-channel LED drivers which turn all LED strings on and off simultaneously. To ensure the highest reliability, the series includes extensive protection features such as over-temperature protection, over-voltage protection, and LED open/short circuit protection. The devices integrate power MOSFETs for the boost converter and channel regulation circuitry, providing design flexibility in a very compact package.

For more information, contact Intersil Corp., 1001 Murphy Ranch Rd., Milpitas, CA 95035. Phone: (408) 432-8888.