Low Power Consumption LCD Backlight 8-LED Driver with Automatic Dimming Function

Semiconductor manufacturer ROHM Co., Ltd. has announced the development of a white LED backlight driver with automatic dimming function capable of driving an industry-high 8 lamps in series. Portable equipment such as mobile phones are showing a greater need for longer operating time due to the increasing number of multimedia and web-based functions, along with the trend towards larger LCDs with higher resolution. As a result, backlight LEDs for LCDs need to be able to drive a greater number of lamps with lower power consumption. This is normally achieved through automatic dimming which adjusts the brightness based on ambient conditions. Conventional white LED driver ICs with automatic dimming can drive a maximum of 7 lamps, due in large part to the maximum voltage resistance at the output. A typical LED driver can only handle panels up to 3.5 inches in size, making it difficult to adjust brightness in large-screen displays.

ROHM's BD60910GU features high output voltage resistance and digital circuitry for automatic dual-dimming functionality. 8 lamps can be driven in series– more than any existing driver with automatic dimming function. A unique brightness sensor control is combined with a PWM dimming circuit, resulting in dimming based not only on ambient light but image brightness as well, reducing power consumption considerably. The BD60910GU is compatible with both logarithmic and linear output, unlike conventional drivers that only support one output format.

An additional consideration for LED drivers with PWM dimming is the decreased communication sensitivity, particularly in mobile phones, due to changes in the output voltage of boost circuits. Conventional designs utilize ferrite beads and other shielding materials as a countermeasure. The BD60910GU integrates a system that minimizes boost voltage during PWM dimming, decreasing noise significantly.

Main features of the BD60910GU

1. Industry-high 8-lamp drive capability with double dimming function
2. Supports both logarithmic and linear output type brightness sensors for broad compatibility
3. Allows switching of the gain control when used with ROHM’s brightness sensor IC (BH1621FVC), enabling brightness measurement over a wide range
4. Backlight current adjusted to 8-bit gradation (256 steps) during automatic dimming based on ambient brightness, reducing flickering dramatically
5. Minimizes boost voltage during PWM dimming for reduced EMI and capacitor noise

8-lamp Backlight LED Driver with Dimming Function for Mobile Phones BD60910GU (PDF:371KB)

Glossary

• Double dimming function
  Performs automatic dimming of the backlight brightness based on both ambient conditions as well as　the image signal.
• One-segment broadcasting
  Japan's terrestrial digital format divides one channel into thirteen "segments" , several of which are bundled to transmit video, audio and other data. One segment is reserved solely for mobile communications. The use of this segment for broadcasting is known as "one-segment" broadcasting. Since the bandwidth is 1/4 the usual size, only low-resolution QVGA (320 × 240 pixels) sized images can be transmitted.
• Forward voltage
  The minimum voltage necessary for lighting an LED. Varies depending on the type of LED. White LEDs feature a forward voltage of approximately 3V per lamp (IF=15mA).
• PWM
  Short for Pulse Width Modulation, a method in which the pulse duty cycle is varied.
• Gain switching function (for brightness sensor)
  A function that switches the brightness level, enabling a wide measurement range.
• Logarithmic output brightness sensor
  A type of photocurrent output that take into account the ambient brightness (lx). Different types of output exist such as linear, logarithmic and PWM output. Logarithmic output can detect a wide range of brightness from indoor to outdoor, making it ideally suited for mobile devices which are often exposed to a variety of environments. Generally speaking, logarithmic output differs from linear output in that it can provide output characteristics close to the human eye.

	LED Drivers ICs for LCD Backlights LED Driver IC Series