To help manufacturers solve these challenges, Freescale Semiconductor has introduced the MC34845 LED driver with high-speed pulse modulation (PWM). This six-channel device allows the LCD backlight to operate at frequencies outside the audio range, eliminating noise and smear. In addition, the accuracy and flexibility of the drive provides display consistency and a wide range of dimming to further enhance the end user experience. Border=0 Freescale's MC34845MC34845LED driver is ideal for backlighting applications with notebook displays that are 7-17 inches or larger, as well as other applications that use multiple low-power LEDs (such as lighting products).
According to a survey by DisplaySearch, the penetration of LED backlights in large (10-inch and above) thin-film transistor (TFT) LCDs is expected to grow from around 7% in the fourth quarter of 2008 to 23% in the fourth quarter of 2009. In 2012, more than half of large TFTLCDs and all notebooks will use LED backlighting.
Factors driving the rapid adoption of LED backlight technology include: energy-saving operation that extends battery life; and the ability to design smaller displays for smaller, lighter notebooks. LED backlighting is an environmentally friendly solution compared to CCFL displays that contain mercury.
Micha el Jennings, market segment manager for display products for Freescale's analog mixed-signal and power management division, believes: "The outstanding performance, accuracy and flexibility of the MC34845 drive help manufacturers avoid LED drivers operating at lower frequencies. Numerous problems. Advanced technologies such as MC34845 will help promote the widespread adoption of LED backlights in the global notebook market."
The high speed LED driver supports PWM up to 100kHz and pulse widths down to 200ns. This feature is suitable for achieving a 1000:1 dimming range at the 25 kHz frequency level and provides excellent linearity in this range, supporting very fine dimming initiatives. The driver is also very accurate, supporting ±2% maximum current matching over the -40 to +85° operating temperature, which helps to improve display consistency. It uses a single direct drive PWM input to drive the output.
The MC34845 also uses a boost converter to generate the required voltage to power the LED. Both versions can be used for the boost switching frequency of 600Khz (MC34845) or 1.2MHz (MC34845A). The input range supports 2 and 3 cell Li-Ion or fixed input power | regulators. The high-voltage output capability allows the device to drive 96 white LEDs with more drivers than the competing 6-channel design. The dynamic margin control automatically sets the output voltage according to the voltage requirements of the LED.
The MC34845 supports low-power shutdown and uses a maximum supply current of only 1uA. In addition, with the automatic shutdown mode, the device shuts down after the PWM input has been inactive for a certain period of time.
Features of the MC34845 product:
Input voltage range: 5V~21V? 2.0A Integrated boost? Switching frequency: 600kHz (MC34845)? Switching frequency: 1.2MHz (MC34845A)? Output voltage: up to 60V? LED current: up to 30mA? Current matching: ±2 %? Direct PWM input control? PWM frequency: up to 100kHz? Dimming range: 50000:1? Minimum pulse: 200ns? Dynamic margin control? LED open/short protection? User programmable OVP? OTP, OCP, UVLO fault detection? Shutdown below 1mA? 24-pin QFN package: 4mm x 4mm x 0.65mm About the Freescale Technology Forum Freescale Technology Forum (FTF) virtual forum will be held July 14-16, 2009, it It is an online supplement to Freescale's existing global FTF program. FIT is designed to inspire innovation and collaboration, and it has now become an annual developer event for the embedded semiconductor industry. Founded in 2005, this forum has attracted more than 28,000 attendees at its FTF conferences around the world.
About Freescale Semiconductor Freescale Semiconductor is a leading global semiconductor company that designs and manufactures embedded semiconductor products for the automotive, consumer, industrial, and networking markets. Headquartered in Austin, Texas, this privately held company has design, R&D, manufacturing and sales facilities around the world.
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