MLX75030 Datasheet, PDF (19/72 Pages) Melexis Microelectronic Systems – Universal ActiveLight Sensor Interface

MLX75030 Universal ActiveLight Sensor Interface
Datasheet
7. Detailed Description
7.1. Analog Sensor Functions
7.1.1. Active Light Sensor
The MLX75030 works with two separate transmit- and receive-channels A and B. In order to perform an active light
measurement, carrier modulated light signal bursts are transmitted by the LED(s) and received by the ActiveLight channel
detectors connected to the pins 9 and 10. Both receive-channels can work separate or in parallel.
The measured ActiveLight signal current is amplified and converted to digital numbers by the on-board ADC by following
formula:
A_{ActiveLigh tADC}
= I _{ActiveLightPD}
4.10 ⁴ * K _DEMOD
* GAIN _ ADJ
50,3 ^µV
_ AA * GAIN _ BUF
+ 2¹⁵
LSB
Where
•
is the ActiveLight signal value in DN
•
is the ActiveLight signal current in uA
•
is a correlation gain value between 0.25 and 0.5, depending on the setting of Tdem bits in register SetAna
•
_ _ is the Anti-aliasing filter gain, set by SetAL and SetBL registers, defaulting to value 2
•
_ is the ADC input buffer gain, set by SetAna and GainBuf registers, defaulting to value 1
It is recommended to use the default values of
.
_ _ and
_ . It is recommended to optimize the value of
7.1.1.1. Active Light Channel DC Light Measurement
The input DC current compensation circuitry of the transimpedance amplifier is able to supply and measure the dc current
supplied to the photodetector. Both active light channels are identical in structure. In order to reach a feasible resolution in
the current range of interest (low currents in the range up to 275uA), the measurement characteristic will saturate for
currents above the I_DC current range, however the compensation circuit is nevertheless able to supply the specified current
levels up to 900uA to the detector. The given ADC word length for the active light channel dc light data is 16Bit.
The DC light measurement can be used to estimate ambient light conditions and compensate DC light dependent
parameters (see next section).
REVISION 005 – DECEMBER 2013
3901075030
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