TSL27711FN TAOS, TSL27711FN Datasheet - Page 10

• Manufacturer Part Number: TSL27711FN
• Description: Light to Digital Converters Light to Digital w/Proximity
• Manufacturer: TAOS

Specifications of TSL27711FN

• Data Bus Width: 16 bit
• Peak Wavelength: 640 nm, 850 nm
• Maximum Operating Frequency: 795 KHz
• Operating Supply Voltage: 2.4 V to 3.6 V
• Operating Current: 175 uA
• Maximum Operating Temperature: + 70 C
• Minimum Operating Temperature: - 30 C
• Interface Type: I2C
• Maximum Fall Time: 300 ns
• Maximum Rise Time: 300 ns
• Mounting Style: SMD/SMT
• Resolution: 16 bit
• Package / Case: DFN-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

TSL2771
LIGHT-TO-DIGITAL CONVERTER
with PROXIMITY SENSING
TAOS100A − FEBRUARY 2010
Calculating Lux
RAW Channel Data
Saturation
10
Copyright E 2010, TAOS Inc.
The lux calculation is a function of several factors including the clear channel count (CDATA), IR channel count
(IRDATA), ALS gain (AGAIN), and ALS integration time (ATIME). The Clear and IR channel information is
used to calculate an IR Factor (IRF) and IR adjusted count (IAC), which indicates the attenuation to the clear
channel to account for the IR content in the signal. The IR Factor is calculated based on empirical device
measurements under different lighting conditions. Count per lux (CPL) is a function of the AGAIN, ATIME, light
attenuation, and a device factor (DF).
Lux is also dependent upon light attenuation, referred to as glass attenuation (GA). This is used to scale
the lux value to account for some interference such as an aperture, neutral density filter, or a light pipe. If light
is attenuated equally across the spectrum (300 nm to 1100 nm), then a linear GA can be used to compensate
for the light loss of the system. If the sensor is exposed to light without an aperture in an open-air system, then
GA is unity. If the GA is nonlinear, then the IR Factor and LPC will need to be derived under the new conditions.
The lux value can be calculated from the following equation:
For the TSL2771x FN package in open air to the light source, this factor is 52.
Lux is calculated as a function of the clear count (CDATA) and IR count (IRDATA). Because all registers are
byte-oriented, 16-bit DATA must be created from two register reads:
Likewise:
The device can saturate if the light is brighter than can be accumulated with the light-to-frequency conversion.
The full scale value for saturation will depend upon the integration time programmed into the device. In
saturation, the device accumulates 1024 counts for each 2.72 ms of integration time programmed. For each
ATIME programmed, the maximum count (saturation level) is the lesser of (1024
There is also a second condition that impacts saturation. If there is ripple in the received signal, such as under
fluorescent lights, then the signal will go in and out of saturation and the value read from clear or IR channel
will be less than the maximum but still have some effects of being saturated. Because of this, it is necessary
to lower gain if channel values are above 70% of the saturated calculation. This is especially true in high gain
mode with AC-modulated light sources that produce flicker. Under this condition, a channel reading may be
slightly below the saturated calculation but in reality be saturated during the peaks, resulting in a value less than
the actual light level.
If the ALS integration time is greater than 172 μs, the saturation level is 50,000, otherwise it is calculated as:
lux = IR Adjusted Count (IAC)
CDATA = 256
IRDATA = 256
SATURATION = 0.75
Where:
IAC = IRF
CPL = Integration Time
×
×
×
CDATAH (r0x15) + CDATA (r0x14)
IRDATAH (r0x17) + IRDATA (r0x16)
CDATA
×
(1024
r
×
×
×
Gain / GA
Counts per lux (CPL)
(256 − ATIME) − 1)
www.taosinc.com
×
DF
r
×
The LUMENOLOGY r Company
(256 − ATIME)) or 65,535.