TSL2572

LIGHT-TO-DIGITAL CONVERTER

TAOS132 − MARCH 2012

7

The LUMENOLOGY

r Company

r

r

Copyright

E 2012, TAOS Inc.

www.taosinc.com

PRINCIPLES OF OPERATION

System State Machine

An internal state machine provides system control of the ALS and wait timer 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 the ALS function is enabled. Once enabled, the device

will execute the Wait and ALS states in sequence as indicated in Figure 6. Upon completion and return to Idle,

the device will automatically begin a new Wait-ALS cycle as long as PON and AEN remain enabled.

If the ALS function generates an interrupt and the Sleep-After-Interrupt (SAI) feature is enabled, the device will

Interrupts section for additional information.

!WEN

& AEN

Sleep

Idle

ALS

Wait

Start

!PON

INT & SAI

WEN &

AEN

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.