Si1133 Data Sheet
UV Index/Ambient Light Sensor IC with I
2
C Interface
The Si1133 is a UV Index Sensor and Ambient Light Sensor with I
2
C digital interface and
programmable-event interrupt output. This sensor IC includes dual 23-bit analog-to-digi-
tal converters, integrated high-sensitivity array of UV, visible and infrared photodiodes,
and digital signal processor. The Si1133 is provided in a 10-lead 2x2 mm DFN package
and capable of operation from 1.62 to 3.6 V over the –40 to +85 °C temperature range.
Applications
• Wearables
• Handsets
• Display backlighting control
• Consumer electronics
KEY FEATURES
• High accuracy UV index sensor (0 to > 20
uV)
• Matches erythermal curve
• Ambient light sensor
• <100 mlx resolution possible, allowing
operation under dark glass
• Up to 128 klx dynamic range possible
across two ADC range settings
• Industry’s lowest power consumption
• 1.62 to 3.6 V supply voltage
• <500 nA standby current
• Internal and external wake support
• Built-in voltage supply monitor and
power-on reset controller
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Si1133 Data Sheet
Feature List
1. Feature List
• High accuracy UV index sensor
• Matches erythermal curve
• Ambient light sensor
• <100 mlx resolution possible, allowing operation under
dark glass<100 mlx resolution possible, allowing operation
under dark glass
• Up to 128 klx dynamic range possible across two ADC
range settings
• Industry’s lowest power consumption
• 1.62 to 3.6 V supply voltage
• <500 nA standby current
• Internal and external wake support
• Built-in voltage supply monitor and power-on reset control-
ler
• Trimmable internal oscillator with typical 1% accuracy
• I2C Serial communications
• Up to 3.4 Mbps data rate
• Slave mode hardware address decoding
• Small package options
• 10-lead 2 x 2 x 0.65 mm QFN
• Temperature Range: –40 to +85 °C
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Si1133 Data Sheet
2 x 2 mm DFN Ordering Guide
2. 2 x 2 mm DFN Ordering Guide
Family
Si113x
DFN OPNs
Si1133-AA00-GMR
ALS
Y
UV Index
Y
Proximity (# of
LED Drivers)
—
HRM
—
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Si1133 Data Sheet
Functional Description
3. Functional Description
The Si1133 is a UV and Ambient Light sensor whose operational state is controlled through registers accessible through the I
2
C inter-
face. The host can command the Si1133 to initiate on-demand UV or Ambient Light measurement. The host can also place the Si1133
in an autonomous operational state where it performs measurements at set intervals and interrupts the host either after each measure-
ment is completed or whenever a set threshold has been crossed. This results in an overall system power saving allowing the host
controller to operate longer in its sleep state instead of polling the Si1133.
Figure 3.1. Si1133 Basic Application
3.1 Ambient Light Sensing
The Si1133 has photodiodes capable of measuring visible and infrared light. However, the visible photodiode is also influenced by infra-
red light. The measurement of illuminance requires the same spectral response as the human eye. If an accurate lux measurement is
desired, the extra IR response of the visible-light photodiode must be compensated. Therefore, to allow the host to make corrections to
the infrared light’s influence, the Si1133 reports the infrared light measurement on a separate channel. The separate visible and IR
photodiodes lend themselves to a variety of algorithmic solutions. The host can then take these two measurements and run an algo-
rithm to derive an equivalent lux level as perceived by a human eye. Having the IR correction algorithm running in the host allows for
the most flexibility in adjusting for system-dependent variables. For example, if the glass used in the system blocks visible light more
than infrared light, the IR correction needs to be adjusted.
If the host is not making any infrared corrections, the infrared measurement can be turned off in the CHAN_LIST parameter.
By default, the measurement parameters are optimized for indoor ambient light levels, where it is possible to detect low light levels. For
operation under direct sunlight, the ADC can be programmed to operate in a high signal operation so that it is possible to measure
direct sunlight without overflowing.
For low-light applications, it is possible to increase the ADC integration time. Normally, the integration time is 24.4 µs. By increasing this
integration time, the ADC can detect light levels as low as 100 mlx. The ADC integration time for the Visible Light Ambient measure-
ment can be programmed independently of the ADC integration time of the Infrared Light Ambient measurement. The independent ADC
parameters allow operation under glass covers having a higher transmittance to Infrared Light than Visible Light.
When operating in the lower signal range, or when the integration time is increased, it is possible to saturate the ADC when the ambient
light suddenly increases. Any overflow condition will have the corresponding data registers report a value of 0xFFddFF for 16-bit mode
and 0x7FFFFF for 24-bit mode. The host can adjust the ADC sensitivity to avoid an overflow condition. If the light levels return to a
range within the capabilities of the ADC, the corresponding data registers begin to operate normally.
The Si1133 can initiate ALS measurements either when explicitly commanded by the host or periodically through an autonomous proc-
ess. Refer to Section
4. Operational Modes
for additional details.
Two ADCs can be used for simultaneous readings of the visible or UV photodiode and black dark current reference photodiode. When
subtracted, these differential measurements remove dark current, reducing noise that enables lower light sensitivity.
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Si1133 Data Sheet
Functional Description
3.2 Ultraviolet (UV) Index Sensing
The UV Index is a number linearly related to the intensity of sunlight reaching the earth and is weighted according to the CIE erythema
Action Spectrum as shown in Figure 4. This weighting is a standardized measure of human skin's response to different wavelengths of
sunlight from UVB to UVA. The UV Index has been standardized by the World Health Organization as shown in the figure below.
Figure 3.2. CIE Erythemal Action Spectrum
Figure 3.3. UV Index Scale
Isolated UV photodiodes that closely match the erythema curve for accurate UV Index measurements. Matching dark current reference
photodiodes are also provided to cancel UV photodiode noise. The typical calibrated UV Index sensor response vs. calculated ideal UV
Index is shown below for several cloudy and sunny days and at various angles of the sun/time of day.
Given the possible variation of the overlay materials above the Si1133, it is generally recommended that outgoing factory calibration be
performed at the outgoing test to decrease system-to-system variation.
The performance of the Si1133 is best when under a Teflon diffuser while diffuser is within +/- 30 degrees of the sensor view angle.
See the plot below.
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