MLX75030 Datasheet, PDF (20/72 Pages) Melexis Microelectronic Systems – Universal ActiveLight Sensor Interface

MLX75030 Universal ActiveLight Sensor Interface
Datasheet
60000
55000
50000
45000
40000
35000
30000
25000
20000
15000
10000
5000
0
0
PDA
PDB
50
100
150
200
250
300
350
400
450
500
Idc [uA]
Figure 3: Typical ActiveLight channel DC measurement characteristics for both channels A and B
7.1.2. ActiveLight Channel DC Light compensation
Under certain operating conditions, the spectral sensitivity of some photodiodes is not constant and varies with the amount
of (infrared) dc-light received. For the ActiveLight measurements this means that the ActiveLight signal can change rapidly if
the sensor experiences highly changing sunlight conditions, even if all other conditions are constant. This results in reduced
ActiveLight signal sensitivity of the system under changing dc-light conditions.
The variation of the ActiveLight signals as a function of DC-light can be partially compensated by automatically adapting the
amplitude of the sensors’ transmitted infrared light pulses for ActiveLight measurement.
In order to make the system as flexible as possible, the compensation can be adapted to different photodiode types by
definition of the compensation characteristics as a piecewise linear curve like described in Figure 4. The values of the 5
corner points of the curve can be defined by the corresponding 4-Bit words PD_COMP_ICx<3:0> (x = 1..5) in the register
maps, see section 7.4. The PD light compensation can be enabled by setting the EN_PDCOMP bit to “1”.
In order to calculate the decimal values PD_COMP_ICx<3:0> (x = 1..5) for a certain photodiode, one has to measure the
relative ActiveLight signal levels p_x at 5 different DC light levels I_{amb_x} while the EN_PDCOMP is set to "0" (a calculation
example is given below, where @ _ is the measured ActiveLight signal at DC light signal _{!"#_$}):
p₀ = pulse level at (I_{amb_0} = 0) = 1 (this is the 100% reference)
A@ Iamb _ 0 − 2¹⁵
p₁ = pulse level at (I_{amb_1} = 10uA) = e.g. 0.97440 = _{A@ Iamb _1− 215}
A@ Iamb _ 0 − 2¹⁵
p₂ = pulse level at (I_{amb_2} = 45uA) = e.g. 0.94224 = _{A@ Iamb _ 2 − 215}
p₃ = pulse level at (I_{amb_3} = 150uA) = e.g. 0.91556 = …
p₄ = pulse level at (I_{amb_4} = 500uA) = e.g. 0.89858 = …
p₅ = pulse level at (I_{amb_5} = 900uA) = e.g. 0.89477 = …
Based on these relative ActiveLight pulse levels, one can calculate the following parameters (x = 1..5):
REVISION 005 – DECEMBER 2013
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