High-speed high-precision digital ambient light sensor (ALS)

The OPT4001 is a light-to-digital sensor (single chip lux meter) that measures

the intensity of visible light. The spectral response of the sensor tightly matches

the photopic response of the human eye. A specially engineered filter on the device

rejects near-infrared component from the common light sources to measure accurate

light intensity. Output of OPT4001 is semi-logarithmic

with 9 binary logarithmic full-scale light ranges along with highly linear response

within each range, bringing capability to measure from 312.5 µlux to 83 klux for PicoStar™ variant and 437.5 µlux to 117 klux for the SOT-5X3 variant. This

capability allows light sensor to have 28-bit effective dynamic range. With built-in

automatic full-scale range selection, logic users do not have to select appropriate

gain settings based on light levels.

The engineered optical filter on OPT4001 provides strong infrared rejection, which aids in

maintaining high accuracy, despite placing the sensor under dark glass, which is common

requirement from industrial design of end products due to aesthetics.

The OPT4001 is

designed for systems that require light level detection to enhance user experience and

typically replaces low accuracy photo diodes, photo-resistors and other ambient light

sensors with underwhelming human eye matching and near infra-red rejection.

The OPT4001

device can be configured to operate with light conversion times all the way from 600 µs to

800 ms in 12 steps, providing system flexibility based on application need. Conversion time

includes the light integration time and ADC conversion time. Resolution of the measurement

is determined by a combination of light intensity and the integration time, effectively

bringing in capability to measure down to 312.5 µlux of light intensity changes for the PicoStar™

variant and 437.5 µlux for the SOT-5X3 variant.

The digital operation is flexible for system

integration. Measurements can be either continuous or triggered in one shots with register

writes or hardware pin (only on SOT-5X3 variant). The device features a threshold detection

logic, which allows the processor to sleep while the sensor watches for appropriate wake-up

event to report via the interrupt pin (only on SOT-5X3 variant).

Digital output, representing the light level

is reported over an I2C and SMBus compatible, two-wire serial interface. An

internal FIFO on output registers is available to read out the measurements from the sensor

at a slower pace while still preserving all the data captured by the device. OPT4001 also supports I2C burst mode helping host read

data from FIFO with minimal I2C overhead.

The low power consumption and low

power-supply voltage capability of the OPT4001 helps enhance

the battery life of battery-powered systems.