MLX90320LFRLFR MELEXIS [Melexis Microelectronic Systems], MLX90320LFRLFR Datasheet - Page 14

• Manufacturer Part Number: MLX90320LFRLFR
• Description: Automotive small sensor interface
• Manufacturer: MELEXIS [Melexis Microelectronic Systems]

The ALU computes equation 2 with 12 bits but the result is truncated to 10 bits because the Gain DAC is a 10 bit
DAC. When the MLX90320 is not able to compensate for the sensor sensitivity drift with temperature, the fine
gain calibration parameters stored in EEPROM will lead to a FNGain
the MLX90320 output voltage will go into a fault band to indicate that the output voltage is not reliable anymore.
Typical total gains with the corresponding sensor offset ranges that can be compensated can be found in table 3.
6.4.2 The Offset calibration of the sensor signal chain.
The purpose of the 7-bit offset DAC is to be able to adjust the MLX90320 output offset anywhere in the 0.5V to
4.5V range. The voltage at the output of the coarse offset DAC can be calculated by the formula:
Equation 3
Explanation of parameters used in equation 1:
The voltage span at the output of the coarse offset DAC is large enough to allow the user to calibrate a
decreasing output characteristic with for example 4.5V as output offset and 0.5V as output full scale. This output
characteristic is only possible by inverting the inputs (setting the IINV bit).
Besides the programmable coarse offset, there is also a 10-bits programmable fine offset stage which allows
adjusting the MLX90320 output offset with a high resolution (at least a resolution of 0.1% of the supply voltage).
The voltage at the output of the fine offset DAC can be calculated by the formula:
3901090320
Rev 004
CSOff
ana
log
T
temperature chain outputs 10bits but 12 bits are stored (address 0 to 2 of the EEPROM). The MSB
must always be 0 and the other 11 bits are obtained from an average of the previous temperature
readings. This gives more accuracy to the output of the temperature chain. The T1 value used in
equation 2 is in the [0..1] range with an 11 bit resolution.
G
the output span at room temperature. 12 bits are stored (address 12 to 14 of the EEPROM) but only
the 10 first are used. The two MSB must be 0. The G
with a 10 bit resolution.
G
temperature. 12 bits are stored (address 8 to 10 of the EEPROM). The MSB is the sign bit (two’s
complement): If G1[11] = 1 then G1 is negative, if G1[11] = 0 then G1 is positive. The G1 value used in
equation 2 is in the [-2..2] range with an 11 bit resolution.
G
temperature. 12 bits are stored (address 4 to 6 of the EEPROM). The MSB is the sign bit (two’s
complement): If G2[11] = 1 then G2 is negative, if G2[11] = 0 then G2 is positive. The G2 value used in
equation 2 is in the [-2..2] range with an 11 bit resolution.
CSOff
CSOff
EEPROM).
1
0
1
2
is the output of the temperature chain corresponding to the room temperature. The ADC of the
is the zero order fine gain coefficient (independent from the temperature) used to adjust accurately
is the second order fine gain coefficient used to compensate the sensor sensitivity drift with
is the first order fine gain coefficient used to compensate the sensor sensitivity drift with
. 4
analog
digital
52
is the digital decimal value of the coarse offset (7 bits stored in address 11 and 15 of the
is the voltage at the output of the coarse offset DAC.
CSOff
127
digital
. 4
52
0
3 .
Page 14 of 32
V
DD
5
Automotive small sensor interface
0
value used in equation 2 is in the [0..1] range
real
value out of the [0..1] range. In this case
MLX90320
Data Sheet
Mar/05