MLX90320_12 Datasheet, PDF (12/33 Pages) Melexis Microelectronic Systems – Automotive sensor interface

6.3 The temperature chain.
MLX90320
Automotive sensor interface
Figure 3 The temperature chain
The temperature chain is composed of the temperature sensor, an amplifier with programmable gain and offset
and a SAR ADC.
The user can choose between an internal or an external temperature sensor. By setting the bit TMP_Select to 1
(EEPROM address 23) the internal temperature sensor is chosen and the TMP pin has to be left floating in
application mode. If TMP_Select is 0 the external temperature sensor is chosen and an external resistor has to
be connected between the supply voltage and the TMP pin. The MLX90320 should be used with an external
temperature sensor in applications where the temperature surrounding the customer sensor is different from the
temperature surrounding the MLX90320. An example of external resistor that could be used in those specific
applications is given in paragraph 8.
As the sensitivity and the offset of the temperature sensor can vary a lot from part to part, the temperature chain
must be calibrated. For that reason the amplifier gain is three bits programmable (TMP_GAIN bits stored in
EEPROM address 31). These three bits are used to calibrate the sensitivity of the temperature chain. The
amplifier offset is five bits programmable (TMP_OFFSET bits stored in EEPROM address 23 and 27) and
compensates the offset of the temperature sensor. After calibration the output of the temperature chain amplifier
must be within the input range of the SAR ADC for the entire application temperature range.
When the calibration of the temperature chain is over, the 10 bits room temperature T1 can be stored in the
EEPROM (address 0 to 3 for the T1 value used to calculate the fine gain and address 16 to 18 for T1 value used
to calculate the fine offset) and it will be used for the sensor signal chain offset and sensitivity temperature drift
compensation.
Remark: Refer to the document AN_MLX90320.pdf for detailed information on how to calibrate the temperature
chain and the sensor signal chain.
3901090320
Rev 007
Page 12 of 33
Data Sheet
Feb/12