TSL2571
LIGHT-TO-DIGITAL CONVERTER
TAOS117A − FEBRUARY 2011
PRINCIPLES OF OPERATION
System State Machine
The device provides control of ALS and power management functionality through an internal state machine
will move to the start state. It will then continue through the Wait and ALS states. If these states are enabled,
the device will execute each function. If the PON bit is set to 0, the state machine will continue until all
conversions are completed and then go into a low power sleep mode.
Sleep
PON = 1 (r 0:b0)
Start
ALS
Wait
PON = 0 (r 0:b0)
Figure 5. Simplified State Diagram
NOTE:
In this document, the nomenclature uses the bit field name in italic followed by the register number and
bit number to allow the user to easily identify the register and bit that controls the function. For example, the
power on (PON) is in register 0, bit 0. This is represented as
PON (r0:b0).
Photodiodes
Conventional silicon detectors respond strongly to infrared light, which the human eye does not see. This can
lead to significant error when the infrared content of the ambient light is high (such as with incandescent lighting)
due to the difference between the silicon detector response and the brightness perceived by the human eye.
This problem is overcome through the use of two photodiodes. The channel 0 photodiode, referred to as the
CH0 channel, is sensitive to both visible and infrared light, while the channel 1 photodiode, referred to as CH1,
is sensitive primarily to infrared light. Two integrating ADCs convert the photodiode currents to digital outputs.
The ADC digital outputs from the two channels are used in a formula to obtain a value that approximates the
human eye response in units of lux.
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