Freescale Carle LED driver MC34845 LCD screen to remove noise and shadow

Light-emitting diode (LED) can make notebook computer more compact with a screen brighter and longer battery life, thus rapidly replacing the cold cathode fluorescent lamp (CCFL), a liquid crystal display screen of notebook computer, industrial and medical use of the monitor (LCD) main backlight technology. However, the use of LED in the notebook LCD technical problems, such as noise and drag, which may affect the end user experience.

To help manufacturers solve these problems, fly think of Carle (Freescale) introduced with high speed pulse modulation (PWM) function of the MC34845 LED drive. The six channel device allows the LCD backlight to operate outside the audio frequency range, thereby eliminating noise and shadow. In addition, the accuracy and flexibility of the drive provides a display of consistency and a wide dimming range to further enhance the end-user experience.

The application of MC34845 LED backlight driver is very suitable for laptop display 7-17 inches above, and other applications using multiple low-power LED (e.g. lighting products).

According to DisplaySearch company, LED backlight in large (10 inches and above) thin film transistor (TFT) LCD in popularity rate is expected in the fourth quarter of 2008 from about 7% to 23% growth in the fourth quarter of 2009. By 2012, more than half of the large TFT LCD and all laptops will use LED backlight.

Factor to promote the rapid adoption of LED backlight technology including: energy saving operation makes the extended battery life; to design more compact display screen, thus achieving more compact and lighter laptops. Compared with mercury containing CCFL display, LED backlight is an environmentally friendly solution.

Freescale Carle analog mixed signal and power management department manager MichaEL Jennings display products market segments: "MC34845 drive outstanding performance, accuracy and flexibility, can help manufacturers avoid many problems occurred in operation of LED drive low frequency at. MC34845 and other advanced technologies will help to promote the use of LED backlight in the global notebook market".

High speed LED drive support width up to 100kHz and PWM to 200ns. The performance is suitable for the 25kHz frequency level to achieve the 1000:1 dimming range, and provide excellent linearity in the range, to support very subtle dimming initiatives. The driver is also very accurate, supporting a maximum current matching of + 2% in the -40 ~+85 operating temperature, which helps to improve the consistency of the display. It uses a single direct drive PWM input to drive the output.

MC34845 also uses a boost converter to generate the required voltage for LED power supply. Two versions can be used for 600Khz (MC34845) or 1.2MHz (MC34845A) boost switching frequency. The input range supports 2 and 3 lithium batteries or fixed input power supplies. High voltage output performance allows the device to drive 96 white LED, the number of drivers more than the competition of the 6 channel design. Dynamic margin control in accordance with the requirements of the LED voltage automatically set the output voltage.

MC34845 supports low-power shutdown, maximum power current using only 1uA. In addition, by virtue of the automatic shutdown mode, the device will not shut down after a certain period of time PWM input.

The characteristics of MC34845 products:

- 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 circuit protection

- user programmable OVP

- OTP, OCP, UVLO fault detection

- shutdown below 1mA

24 pin QFN package: 4 mm x 4 mm x 0.65 mm

Pricing and delivery information

Freescale Carle is currently offering MC34845 (9600kHz boost) and MC34845A (1.2MHz boost) LED drive sample. When the number of two devices reached 10000, the proposed retail price of $1.15.