TMD2772
DIGITAL ALS
and PROXIMITY MODULE
TAOS147E − DECEMBER 2012
PRINCIPLES OF OPERATION
System State Machine
An internal state machine provides system control of the ALS, proximity detection, and power management
features of the device. At power up, an internal power-on-reset initializes the device and puts it in a low-power
Sleep state.
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When a start condition is detected on the I C bus, the device transitions to the Idle state where it checks the
Enable register (0x00) PON bit. If PON is disabled, the device will return to the Sleep state to save power.
Otherwise, the device will remain in the Idle state until a proximity or ALS function is enabled. Once enabled,
the device will execute the Prox, Wait, and ALS states in sequence as indicated in Figure 5. Upon completion
and return to Idle, the device will automatically begin a new prox−wait−ALS cycle as long as PON and either
PEN or AEN remain enabled.
If the Prox or ALS function generates an interrupt and the Sleep-After-Interrupt (SAI) feature is enabled, the
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device will transition to the Sleep state and remain in a low-power mode until an I C command is received. See
the Interrupts section for additional information.
Sleep
I2C
!PON
Start
Idle
INT & SAI
INT & SAI
PEN
!PEN &
!WEN
& AEN
!WEN
& !AEN
!PEN &
WEN &
AEN
!AEN
ALS
Prox
!WEN
& AEN
WEN
AEN
Wait
Figure 6. Simplified State Diagram
Photodiodes
Conventional ALS 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).
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.
Copyright E 2012, TAOS Inc.
The LUMENOLOGY r Company
r
r
www.taosinc.com
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