Maxim is introducing the MAX44007/MAX44009 digital ambient light sensor (ALS) ICs with a unique adaptive gain block. Designed using the company’s proprietary BiCMOS technology, these ICs integrate two optical sensors, an ADC and digital functionality into a 2 x 2 x 0,6 mm package.
The devices offer a unique interrupt function that constantly measures the amount of light and reports to the microcontroller when the measurement passes a threshold. This functionality extends power savings by reducing the frequency of I²C communications. Maximum total gain error is as little as 15% and digital communication 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 a highly accurate lux response. Moreover, the ADC integration time of the sensors can be adjusted from 6,25 ms to 800 ms. A default integration time of 100 ms ensures 50 Hz/60 Hz rejection.
Handheld devices frequently employ tinted or black glass on top of the sensor. This causes many challenges for the light sensor, since black glass shifts the response to various light sources, all of which have different light emission spectra. Measurement errors typically result when these different spectra are combined with the spectrum profile of the glass. 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 enhanced 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 the time-consuming process of manually programming the device, and it offloads work from the application processor or microcontroller. Additionally, it provides an extremely 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 1.
The ICs boast an operating current of just 0,65 μA and operate from a 1,7 V to 3,6 V supply voltage. This allows them to use the same 1,8 V supply for both the supply voltage and the I²C interface. An address pin allows the use of two sensors on the same I²C bus.
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