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TMD2771 Datasheet(PDF) 3 Page - List of Unclassifed Manufacturers |
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3 / 33 page 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 VDD 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, buffers, comparators, a state machine, and an I2C interface. Each device combines one photodiode (CH0), 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. Communication with the device is accomplished through a fast (up to 400 kHz), two-wire I2C serial bus for easy 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. |
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