MLX75030 Datasheet, PDF (22/72 Pages) Melexis Microelectronic Systems – Universal ActiveLight Sensor Interface

MLX75030 Universal ActiveLight Sensor Interface
Datasheet
Figure 4: Example of a compensation curve I_COMP for I_{C_5}=0. The dc-currents of the corner points are fixed in the design and cannot
be influenced. The compensation components I_{C_1}…I_{C_5} are defined by the registers DC_COMP_IC1…5 with 4 bits each. The
resulting compensation characteristics are shown in the black graph.
7.1.3. Ambient Light Sensor
7.1.3.1. Normal Operation
The ambient light detection system of the MLX75030 consists of two independent channels C and D and an on-chip
controllable dedicated ground pin GNDAMB. GNDAMB should not be directly connected to GND. An external photodiode is
connected in between each channel and GNDAMB.
The ambient light signal is low pass filtered on chip.
The signal of a 1ms switched-capacitor filters is sampled by the ADC (on request by an SPI command, each 2.5ms), where it is
converted into a 16bit digital word.
The total input stage, this means from the external diode up to the 1ms filter, has a cut-off frequency at ~160Hz. Sampling
this output every 2.5ms, commanded by SPI, would make a sample rate of 400Hz, which well above the Nyquist frequency of
the present frequency content of 160Hz.
Within the specified input current range the ambient input stages bias the external photodiodes with > 0V in normal
operation.
7.1.3.2. Calibration and temperature compensation
The output of each ambient channel has a strong temperature dependence and a slight process dependence that can be
compensated at run time. This is shown in following equation (channel x, where x = C or D):
( ) e I_x
= 1 + TC_Iref
∆T
1+ α

O_x
300²
∆T


α _{}
ambout_x
T
−
2¹⁵

+
β
(1)
REVISION 005 – DECEMBER 2013
3901075030
PAGE 22 OF 72