The First Digital Ambient Light Sensor Compatible with I²C Bus Hs Mode

ROHM Co., Ltd., in response to market demand for faster internal transmission speeds in mobile phones to keep pace with increasing functionality, has announced the development of a digital brightness sensor IC that supports the new I²C bus Hs (High-speed) mode – an industry first. Internal signal transfer rates are increased by up to 8.5 times over the conventional Fast mode. This development is expected to trigger widespread use mobile phones while enabling even greater functionality.

Minimizing LCD backlight power in mobile phones is becoming an increasingly important consideration, especially given the continual progression towards greater functionality. Many devices now implement some type of brightness control, normally by utilizing a microcontroller and LED driver along with an ambient light sensor. However, this requires relatively fast bus speed, making the current I²C bus transmission mode (Fast), with a transmission speed of only 400Kbits/s, a potential obstacle to increased performance and functionality in future smart phones.

The BH1780GLI answers this demand by supporting the new Hs mode that stipulates a transfer rate of 3.4Mbit/sec. Additional features include a high-precision A/D converter with a wide output range (0-65,535 lux, in 1 lux incremenents) for measuring ambient light from darkness to direct sunlight, along with spectral sensitivity characteristics similar to the human eye that is stable across different light sources (i.e. incandescent/fluorescent lamps, sunlight). A noise elimination function is also built in for reliable operation regardless of power source fluctuations (e.g. AC oscillation). In addition, unique laser trimming technology limits sensitivity variations to ±20%.

Digital Ambient Light Sensor IC Compatible with I2C Bus Hs Mode  「BH1780GLI」(PDF：128KB)

■Key Features

1. Supports I²C bus Hs mode (max. 3.4Mbit/s）
2. Brightness level output digitally (0 to 65,535 lux)
3. 50Hz/60Hz optical noise elimination function ensures stable brightness measurement
4. Sensitivity variation: ±20％
5. UV-blocking resin package eliminates adverse effects from UV light

■Specifications

Part No.	Output Type	Source Voltage (V)	Sensitivity Variation (%)	Brightness Measurement Range (lx)	Operating Temperature Range (ºC)	Package
						Type	Dimensions
BH1780GLI	Serial 16bit	2.3 to 3.0	±20	0 to 65535	−40 to +85	WLGA04IW02	2.0×2.0 h=0.8 max

■Terminology

• I²C Bus Interface
  I²C stands for Inter-Integrated Circuit – a type of serial bus developed by Philips designed for connecting low-speed peripheral devices to the mainboard. It is widely used in a number of electronic devices, including mobile phones. Different modes exist, based on the bitrate: Standard mode, Fast mode, and high-speed (Hs) mode.

■Sensitivity Ratio* Comparison　※Ratios for various light sources, taking the value for fluorescent lights as 1

Ambient Light Sensor IC Series