TMD27721 Datasheet, PDF (11/35 Pages) TEXAS ADVANCED OPTOELECTRONIC SOLUTIONS – DIGITAL ALS and PROXIMITY MODULE

TMD2772
DIGITAL ALS
and PROXIMITY MODULE
TAOS147E − DECEMBER 2012
ALS Operation
The ALS engine contains ALS gain control (AGAIN) and two integrating analog-to-digital converters (ADC), one
for the CH0 and one for the CH1 photodiodes. The ALS integration time (ATIME) impacts both the resolution
and the sensitivity of the ALS reading. Integration of both channels occurs simultaneously and upon completion
of the conversion cycle, the results are transferred to the data registers (C0DATA and C1DATA). This data is
also referred to as channel count. The transfers are double-buffered to ensure data integrity.
ATIME(r 1)
2.73 ms to 699 ms
valid ^CH0
CH0
ALS
CH0
Data
ALS Control
CH1
ADC
CH1
Data
C0DATAH(r0x15), C0DATA(r0x14)
C1DATAH(r0x17), C1DATA(r0x16)
ill CH1
AGAIN(r0x0F, b1:0)
1y, 8y, 16y, 120y Gain
t _{Figure 7. ALS Operation}
G _{s The registers for programming the integration and wait times are a 2’s compliment values. The actual time can}
A ^{t be calculated as follows:}
ATIME = 256 − Integration Time / 2.73 ms
s ^{n Inversely, the time can be calculated from the register value as follows:}
e ^{Integration Time = 2.73 ms × (256 − ATIME)}
m ^{t In order to reject 50/60-Hz ripple strongly present in fluorescent lighting, the integration time needs to}
be programmed in multiples of 10 / 8.3 ms or the half cycle time. Both frequencies can be rejected with a
a ^{n programmed value of 50 ms (ATIME = 0xED) or multiples of 50 ms (i.e. 100, 150, 200, 400, 600).}
The registers for programming the AGAIN hold a two-bit value representing a gain of 1×, 8×, 16×, or 120×. The
o _{gain, in terms of amount of gain, will be represented by the value AGAINx, i.e. AGAINx = 1, 8, 16, or 120. With}
c ^{the AGL bit set, the gains will be lowered to 1/6, 8/6, 16/6, and 20×, allowing for up to 60k lux.}
l Lux Equation
a The lux calculation is a function of CH0 channel count (C0DATA), CH1 channel count (C1DATA), ALS gain
(AGAINx), and ALS integration time in milliseconds (ATIME_ms). If an aperture, glass/plastic, or a light pipe
ic ^{attenuates the light equally across the spectrum (300 nm to 1100 nm), then a scaling factor referred to as glass}
attenuation (GA) can be used to compensate for attenuation. For a device in open air with no aperture or
glass/plastic above the device, GA = 1. If it is not spectrally flat, then a custom lux equation with new coefficients
n _{should be generated. (See TAOS application note).}
h ^{Counts per Lux (CPL) needs to be calculated only when ATIME or AGAIN is changed, otherwise it remains a}
constant. The first segment of the equation (Lux1) covers fluorescent and incandescent light. The second
c segment (Lux2) covers dimmed incandescent light. The final lux is the maximum of Lux1, Lux2, or 0.
e^{CPL = (ATIME_ms × AGAINx) / 20}
Lux1 = (C0DATA − 1.75 × C1DATA) / CPL
T^{Lux2 = (0.63 × C0DATA − 1.00 × C1DATA) / CPL}
Lux = MAX(Lux1, Lux2, 0)
Copyright E 2012, TAOS Inc.
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