LED Driver Eliminates Audible Noise And Visual Artifacts

The six-channel MC34845 LED driver with high-speed PWM capability is designed to allow LED backlights to operate at frequencies above the audible range, thereby eliminating noise issues and reducing visual artifacts. In addition, the driver’s accuracy and flexibility offer display uniformity and a wide dimming range to further enhance end-user experience. It’s ideal for backlighting applications in notebook displays ranging in size from seven inches to more than 17 inches, as well as other applications that use multiple low-power LEDs. The high-speed LED driver supports up to 100-kHz PWM, with pulses down to 200 ns. This performance is suitable for 1000:1 dimming range at 25 kHz with excellent linearity across the range, supporting imperceptible dimming steps. The driver supports ±2% current matching maximum across the operating range of -40°C to +85°C, which helps improve display uniformity. The outputs are driven using a single direct drive PWM input. A boost converter produces the required voltage to power LEDs. Two versions are available for boost switching frequencies of either 600 KHz (MC34845) or 1.2 MHz (MC34845A). The input range supports 2-cell and 3-cell lithium-ion batteries or a fixed-input supply. High-voltage output capability enables the device to drive up to 96 white LEDs. The driver is housed in a 24-Ld QFN 4 mm x 4 mm x 0.65 mm package. Both devices are sampling now. Pricing is set at $1.15 in 10,000-unit quantities. FREESCALE SEMICONDUCTOR, Austin, TX. (800) 521-6274.