TSL2772

LIGHT-TO-DIGITAL CONVERTER

with PROXIMITY SENSING

TAOS131 − DECEMBER 2011

9

The LUMENOLOGY

r Company

r

r

Copyright

E 2011, TAOS Inc.

www.taosinc.com

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.

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 9. 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

the Interrupts section for additional information.

!PEN &

!WEN

& AEN

!WEN

& !AEN

PEN

Sleep

Idle

Wait

ALS

Prox

Start

!PON

INT & SAI

AEN

WEN

INT & SAI

!AEN

!PEN &

WEN &

AEN

!WEN

& AEN

Figure 9. 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.