TSL2771

LIGHT-TO-DIGITAL CONVERTER

with PROXIMITY SENSING

TAOS100B − FEBRUARY 2011

2

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Copyright

E 2011, TAOS Inc.

The LUMENOLOGY

r Company

www.taosinc.com

Functional Block Diagram

CH0

SDA

INT

SCL

LDR

CH1

ADC

ALS Control

CH1

Data

Wait Control

Prox

ADC

Prox Control

Prox

Data

IR LED Constant

Current Sink

CH0

ADC

CH0

Data

Prox

Integration

CH1

Upper Limit

Upper Limit

Lower Limit

Lower Limit

Interrupt

GND

Detailed Description

The TSL2771 light-to-digital device provides on-chip photodiodes, integrating amplifiers, ADCs, accumulators,

photodiode (CH0), which is responsive to both visible and infrared light, and a channel 1 photodiode (CH1),

which is responsive primarily to infrared light. Two integrating ADCs simultaneously convert the amplified

photodiode currents into a digital value providing up to 16 bits of resolution. Upon completion of the conversion

cycle, the conversion result is transferred to the data registers. This digital output can be read by a

microprocessor through which the illuminance (ambient light level) in Lux is derived using an empirical formula

to approximate the human eye response.

connection to a microcontroller or embedded controller. The digital output of the device is inherently more

immune to noise when compared to an analog interface.

The device provides a separate pin for level-style interrupts. When interrupts are enabled and a pre-set value

is exceeded, the interrupt pin is asserted and remains asserted until cleared by the controlling firmware. The

interrupt feature simplifies and improves system efficiency by eliminating the need to poll a sensor for a light

intensity or proximity value. An interrupt is generated when the value of an ALS or proximity conversion exceeds

either an upper or lower threshold. In addition, a programmable interrupt persistence feature allows the user

to determine how many consecutive exceeded thresholds are necessary to trigger an interrupt. Interrupt

thresholds and persistence settings are configured independently for both ALS and proximity.

Proximity detection requires only a single external IR LED. An internal LED driver can be configured to provide

a constant current sink of 12.5 mA, 25 mA, 50 mA, or 100 mA of current. No external current limiting resistor

is required. The number of proximity LED pulses can be programmed from 1 to 255 pulses. Each pulse has a

16-

μs period. This LED current, coupled with the programmable number of pulses, provides a 2000:1

contiguous dynamic range.