Compact Optical Sensor ICs Suit Portable Systems

At Mobile World Congress 2011, Maxim Integrated Products is introducing the Max44007/Max44009, digital ambient-light sensor (ALS) ICs with an adaptive-gain block, suitable for smartphones and TVs. Designed using the company's proprietary BiCMOS technology, these ICs integrate two optical sensors, an ADC and digital functionality into a tiny 2x 2 x 0.6mm package. This integration saves valuable board space while delivering the industry's highest performance.

The Max44007/Max44009 are suitable for applications such as tablet and notebook PCs, smartphones, TVs, digital lighting-management systems and light-intensity monitoring applications. According to Maxim, the ICs consume 100x less power than the nearest competitive product, significantly extending battery life. They offer a unique interrupt function that constantly measures the amount of light and reports to the microcontroller when the measurement passes the threshold. This functionality extends power savings by reducing the frequency of I2C communications.

In addition to providing precise light measurement, the digital communication of Maxim's light sensors is immune to parasitics on the communication interface. Maxim's BiCMOS technology enables the integration of two photodiodes along with an optical filter to reject ultraviolet and infrared light. This allows the Max44007/Max44009 to replicate the optical response of the human eye and accurately measure visible light in a variety of environmental settings. Advanced algorithms correct for any spectra variations between light sources, ensuring an accurate lux response.

Moreover, the ADC integration time of the sensors can be adjusted from 6.25ms to 800ms. A default integration time of 100ms ensures excellent 50Hz/60Hz rejection. Hand-held devices frequently employ tinted or black glass on top of the sensor, which creates challenges for the light sensor, since black glass shifts the response to various light sources. The Max44007 provides access to two different optical sensors: a visible-plus-infrared photodiode and an infrared photodiode. Once the designer knows the response of the black glass, it can be factored into the light sensor's measurement for superior accuracy and sensitivity (down to 0.025 lux).

Ambient-light sensors require the widest dynamic range possible to support a broad spectrum of light conditions, from direct sunlight to complete darkness with every variation in between. Even in digital light sensors, the gain has to be set to a certain value to address different modes of operation in multiple light scenarios. This added configuration requirement increases both design complexity and time to market. The Max44007/Max44009 feature an integrated adaptive-gain block that automatically selects the optimum gain range.

This capability relieves designers of having to manually programme the device and also offloads work from the application processor or microcontroller. Additionally, it provides a wide dynamic range. The Max44009 can measure light levels from 0.045 lux to 188,000 lux, yielding a dynamic range of more than 4,000,000 to one. Designed to meet tight power budgets, the ICs boast an operating current of 0.65uA, which is lower than the power-down current of many competitive products. Furthermore, they operate from an industry-low 1.7V to 3.6V supply voltage.

Consuming as little as 1.1uW of operating power, Maxim's solutions use 100x less power than the nearest competitor. As an added benefit, the devices' low supply voltage allows them to use the same 1.8V supply for both the supply voltage and the I2C interface. This reduces power consumption and design complexity by only requiring a single voltage rail for the part. An address pin allows the use of two sensors on the same I2C bus. Designed for the tight space requirements of portable systems, the Max44007/Max44009 are offered in a lead-free, 2 x 2 x 0.6mm, six-pin UTDFN-Opto-EP package. Prices start at $1.20 (?0.74) for quantities of 1,000-up, FOB USA.

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