Freescale Semiconductor has introduced the MC34845 LED driver with high-speed pulse width modulation (PWM) capability. This six-channel device 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 experiences.
The MC34845 LED driver is well suited 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, such as lighting products.
"The outstanding performance, accuracy and flexibility of the MC34845 driver helps manufacturers avoid a host of issues associated with LED drivers operating at lower frequencies," said Michael Jennings, Market Segment Manager for Display Products in Freescale’s Analog, Mixed-Signal and Power Division. "Advanced technologies such as the MC34845 are helping fuel the rapid adoption of LED backlights in notebook PC markets worldwide."
The high-speed LED driver supports up to 100 kHz PWM, with pulses down to 200ns. This performance is suitable for 1000:1 dimming range at 25 kHz with excellent linearity across the range, supporting imperceptible dimming steps. The driver is also very accurate, supporting ±2% current matching maximum across the operating range of -40 to +85°C, which helps improve display uniformity. The outputs are driven using a single direct drive PWM input.
The MC34845 also features a boost converter to produce 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, more than competing 6-channel designs. A dynamic headroom control automatically sets the output voltage depending on the voltage requirements of the LEDs.
The MC34845 supports low-power shutdown with 1µA max supply current. In addition, an auto shutdown mode can enable the device to enter shutdown after a period of inactivity on the PWM input.
Freescale is currently sampling the MC34845 (600 kHz boost) and the MC34845A (1.2 MHz boost) LED drivers. Both devices are available at a suggested resale price of $1.15 (USD) in 10,000-unit quantities.