TMD2771

DIGITAL ALS

and PROXIMITY MODULE

TAOS143B − SEPTEMBER 2012

2

r

r

Copyright

E 2012, TAOS Inc.

The LUMENOLOGY

r Company

www.taosinc.com

Functional Block Diagram

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

Upper Limit

Upper Limit

Lower Limit

Lower Limit

Interrupt

GND

LEDA

LEDK

Channel 1

Channel 0

Detailed Description

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

which is responsive to both visible and infrared light, and a second photodiode (CH1), which is responsive

primarily to infrared light. Two integrating ADCs simultaneously convert the amplified photodiode currents to

a digital value providing up to 16-bits of resolution. Upon completion of the conversion cycle, the conversion

result is transferred to the Ch0 and Ch1 data registers. This digital output can be read by a microprocessor

where the luminance (ambient light level in lux) is derived using an empirical formula to approximate the human

eye response.

A fully integrated proximity detection solution is provided with an 850-nm IR LED, LED driver circuit, and

proximity detection engine. An internal LED driver (LDR) pin, is connected to the LED cathode (LEDK) to provide

a factory calibrated proximity of 100 mm,

± 20 mm. This is accomplished with a proprietary current calibration

technique that accounts for all variances in silicon, optics, package, and most important, IR LED output power.

This eliminates or greatly reduces the need for factory calibration that is required for most discrete proximity

sensor solutions. While the device is factory calibrated at a given pulse count, the number of proximity LED

pulses can be programmed from 1 to 255 pulses, which allows different proximity distances to be achieved.

Each pulse has a 16

μs period with a 7.2 μs on time.

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

immune to noise when compared to an analog photodiode 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.