Freescale LED backlight driver cuts noise with PWM
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.
The MC34845 LED driver is suitable 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 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 degrees C to +85 degrees 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 1uA 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.