Texas Instruments | How to Select an Ambient Light Sensor for Your End Equipment (Rev. B) | Application notes | Texas Instruments How to Select an Ambient Light Sensor for Your End Equipment (Rev. B) Application notes

Texas Instruments How to Select an Ambient Light Sensor for Your End Equipment (Rev. B) Application notes
How to Select an Ambient Light Sensor for Your System
When designing an application with an ambient light
sensor, there are four main concerns or problems that
must be addressed. The most important features of an
ambient light sensor are spectral response, power,
size, and range of lux measurement.
DC/DC
Point of Load
Point of Load
LDO
MPU
PMIC
Amp
Speaker
In many applications, ambient light sensors are used
to set the display brightness based on the surrounding
light conditions or variables. These use cases need
light measurement at specific wavelengths, like
spectroscopy and ultra-violet (UV) measurement. The
ambient light sensor is used to measure optical energy
at a specific wavelength or specific bands of
wavelengths on the light spectrum.
The goal of these applications is to improve the visual
experience and make the lighting comfortable for the
end user. It is important to regulate lighting based on
the surrounding variables to improve user experience
in mobile displays, thermostats, and more. It is also
important to ensure safety in specific applications like
automotive center stacks and head-up displays (HUD),
because overly bright lights in these application can
distract the user, while dim lights can be difficult to
see.
In some applications, the spectral response of the
sensor must tightly match the photopic response of the
human eye, and also include significant infrared
rejection. Applications that require human eye
responses include IP cameras, tablets, thermostats,
and wearables.
Some applications do not require human eye
responses, and instead can use a wide spectral
bandwidth. For example, applications like video
doorbells (Figure 1) or indoor lighting can sometimes
use a wide spectral bandwidth.
The OPT3002 has a wide spectral bandwidth, ranging
from 300 nm to 1000 nm. The OPT3001, OPT3004,
OPT3007, and OPT3001-Q1 have human eye
responses.
FETs
ORing
Controller
Amp
Wide Vin Buck
Converter
Signal Input/Output
Protection
Protection
Digital
Media
Processor
Output User Interface
DAC
LED Driver
Environmental Sensing
Ambient Light
Sensor
CCD/CMOS
Speaker
IR LED
CHIME
Battery Fuel
Gauge
ADC
Audio CODEC
Selection
Battery
Charger
Audio Interface
Microphone
Non-Isolated AC/DC Power
Supply
Backup Battery
120 V AC
Energy Storage
Non-Isolated DC/DC Power Supply
24 V AC
Introduction
Real Time
Clock
Voltage
Supervisor
IR LED Illumination
Temperature
Monitor
LED
Driver
Self-Diagnostics/
Monitoring
Door Bell
Switch
LED String
Digital Processing
Wireless Interface
Wi-Fi Radio
Sub 1-GHz or
2.5-GHz Radio
Motor Driver
Motor Driver
IR CUT
FILTER
Memory
PIR
Sensor
Motion Detection
LED
Driver
DDR
Termination
DDR Memory
Voltage
Transistors
Flash
Figure 1. Video Doorbell Block Diagram Example
Another design challenge for engineers is how to
extend the battery life of certain applications. Displays
consume approximately 30% to 40% of the power
budget in most equipment, which is critical in
wearables, mobile units, tablets, and other devices,
because these applications run on batteries 90% of
the time.
Controlling the display intensity based on ambient
conditions can help conserve power. The lifetime of
the display can also increase by running at lower
power. One feature of the OPT3002 is the ultra-low
power at approximately 2 µA. The low power
consumption of the device allows the OPT3002 to be
used as a low-power, battery-operated wake-up
sensor when an enclosed system is opened.
Engineers must also consider the size of their system
when they choose an ambient light sensor for their
applications. For the personal electronics industry
(smart phones, notebook PCs, tablets, and so forth), a
small form factor is extremely important because these
applications are generally in a small enclosure.
The OPT3007 has a nominal body size of 0.856 mm ×
0.946 mm × 0.226 mm, and the device comes in a
picostar package. The four active pins in the 6-pin
package enable the PCB designer to create a bigger
opening to the active sensor area.
The OPT3004 offers similar features to the OPT3001,
but the OPT3004 has an improved angular IR rejection
that is beneficial in video surveillance applications.
SBEA006B – April 2018 – Revised November 2019
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How to Select an Ambient Light Sensor for Your System
Copyright © 2018–2019, Texas Instruments Incorporated
1
www.ti.com
The final design consideration for ambient light
sensors is the range of lux measurement. The
OPT3002 has a wide spectral bandwidth that ranges
from 300 nm to 1000 nm. The built-in, full-scale setting
feature of the OPT3002 can measure lux from 1.2
nW/cm2 up to 10 mW/cm2 without prompting the user
to manually select the full-scale range. This capability
allows light measurement over a 23-bit effective
dynamic range.
The results are compensated for dark-current effects,
as well as for other temperature variations. For the
OPT3004, OPT3007, and OPT3001-Q1, the built-in,
full-scale setting feature can measure 0.01 lux up to
83-k lux without the need to manually select the fullscale ranges. This capability also allows light
measurement over a 23-bit effective dynamic range.
With certain applications like IP cameras that require
IR light for night vision, angular IR rejection is an
important feature that can prevent false reads.
TheOPT3004 has an increased angular IR rejection for
these types of applications.
For automotive applications, or end equipments that
are influenced by high temperatures, Texas
Instruments offers the automotive-grade OPT3001-Q1
ambient light sensor. The OPT3001-Q1 offers both
AEC-Q100 grade 2 (–40°C to 105°C) and grade 3
(–40°C to 85°C) qualifications.
With these added qualifications, the OPT3001-Q1 can
be placed in many applications, like automotive
infotainment and clusters.
TheOPT3001, OPT3004, OPT3007, and OPT3001-Q1
are single-chip lux meters that can measure the
intensity of light visible to the human eye. The
precision of the spectral responses, along with the
strong IR rejections, allow these devices to accurately
measure the intensity of light as seen by the human
eye, regardless of the light source.
The strong IR rejection also helps maintain high
accuracy when industrial designs must mount light
sensors under dark glass for aesthetics. These parts
are designed for systems that create light-based
experiences for humans, and these parts can be a
preferred replacement for photodiodes, photoresistors,
or other ambient light sensors with less human eye
matching and weaker IR rejection.
For a summary of the OPT300x parts, see Table 1.
Table 1. Device Comparison Table
OPT3001
OPT3002
OPT3004
OPT3007
OPT3001-Q1
Human Eye
300 nm to
1000 nm
Human Eye
Human Eye
Human Eye
23-Bit
Effective
Dynamic
Range
23-Bit
Effective
Dynamic
Range
23-Bit
Effective
Dynamic
Range
23-Bit
Effective
Dynamic
Range
23-Bit
Effective
Dynamic
Range
Current
Consumptio
n
1.8 µA
1.8 µA
1.8 µA
1.8 µA
1.8 µA
Supply
Range
1.6 V to
3.6 V
1.6 V to
3.6 V
1.6 V to
3.6 V
1.6 V to
3.6 V
1.6 V to
3.6 V
Temp Range
-40 to 85°C
-40 to
85°C
-40 to 85°C
-40 to 85°C
-40 to 85°C
(Grade 3) -40
to 105°C
(Grade 2)
Package
USON6 (2
mm × 2
mm)
USON6 (2
mm × 2
mm)
USON6 (2
mm × 2
mm)
PICOSTAR
(0.9 x 0.8 x
0.226mm)
USON6 (2 mm
× 2 mm)
Notes
Better
Sensitivity
Low Cost
ALS
Better
Angular IR
Rejection
Thinnest ALS
4 pin
operation
Automotive
Grade
Optical
Range/
Filter
ADC
Conclusion
In summary, the main design considerations for an
ambient light sensor in an application are the spectral
response, power, size, and measurement range. The
OPT300x devices are sensors that measure the
intensity of visible light, and are suitable for display
applications.
The spectral responses of the OPT300x sensors
tightly match the response of the human eye, include
significant infrared rejection, have ultra-low power, and
offer small size options. The only exception is the
OPT3002, which has an optical range of 300 nm to
1000 nm and has no human eye response.
2
How to Select an Ambient Light Sensor for Your System
Table 2. Related Documentation
DEVICE
DESCRIPTION
OPT3001 Evaluation Module (EVM)
OPT3001EVM User's Guide
OPT3002 Evaluation Module (EVM)
OPT3002EVM User's Guide
OPT3004 Evaluation Module (EVM)
OPT3004EVM User's Guide
SBEA006B – April 2018 – Revised November 2019
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