TMD2672

DIGITAL PROXIMITY DETECTOR

TAOS149C − AUGUST 2012

10

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Copyright

E 2012, TAOS Inc.

The LUMENOLOGY

r Company

www.taosinc.com

Referring again to Figure 8, the reflected IR LED and the background energy is integrated during the LED On

time, then during the LED Off time, the integrated background energy is subtracted from the LED On time

energy, leaving the IR LED energy to accumulate from pulse to pulse. During LED On time integration, the

proximity saturation bit in the Status register (0x13) will be set if the integrator saturates. This condition can occur

if the proximity gain is set too high for the lighting conditions, such as in the presence of bright sunlight. Once

asserted, PSAT will remain set until a special function proximity interrupt clear command is received from the

host (see command register).

After the programmed number of proximity pulses have been generated, the proximity ADC converts and scales

the proximity measurement to a 16-bit value, then stores the result in two 8-bit proximity data (PDATAx)

registers. ADC scaling is controlled by the proximity ADC conversion time (PTIME) which is programmable from

1 to 256 2.73-ms time units. However, depending on the application, scaling the proximity data will equally scale

any accumulated noise. Therefore, in general, it is recommended to leave PTIME at the default value of one

2.73-ms ADC conversion time (0xFF).

In many practical proximity applications, a number of optical system and environmental conditions can produce

an offset in the proximity measurement result. To counter these effects, a proximity offset (POFFSET) is

provided which allows the proximity data to be shifted positive or negative. Additional information on the use

of the proximity offset feature is provided in available TAOS application notes.

Once the first proximity cycle has completed, the proximity valid (PVALID) bit in the Status register will be set

and remain set until the proximity detection function is disabled (PEN).

For additional information on using the proximity detection function behind glass and for optical system design

guidance, please see available TAOS application notes.