MLX90614ESF-ACC Melexis Inc, MLX90614ESF-ACC Datasheet - Page 26

• Manufacturer Part Number: MLX90614ESF-ACC
• Description: INFRARED THERMOMETER
• Manufacturer: Melexis Inc

Specifications of MLX90614ESF-ACC

• Function: Thermometer, Thermostat
• Topology: ADC (Sigma Delta), Voltage Regulator
• Sensor Type: Internal
• Sensing Temperature: -40°C ~ 85°C
• Output Type: PWM, SMBus™
• Output Alarm: No
• Output Fan: No
• Voltage - Supply: 4 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Through Hole
• Package / Case: TO-39
• For Use With: EVB90614 - BOARD EVAL FOR MLX90614
• Lead Free Status / RoHS Status: Vendor undefined / Vendor undefined
• Other names: Q4002160

8.7 Computation of ambient and object temperatures
The IR sensor consists of serial connected thermo-couples with cold junctions placed at thick chip substrate
and hot junctions, placed over thin membrane. The IR radiation absorbed from the membrane heats (or
cools) it. The thermopile output signal is:
Where To is the object temperature absolute (Kelvin) temperature, Ta is the sensor die absolute (Kelvin)
temperature, and A is the overall sensitivity.
An on board temperature sensor is needed to measure the chip temperature. After measurement of the
output of both sensors, the corresponding ambient and object temperatures can be calculated. These
calculations are done by the internal DSP, which produces digital outputs, linearly proportional to measured
temperatures.
8.7.1 Ambient temperature Ta
The Sensor die temperature is measured with a PTC or a PTAT element. All the sensors conditioning and
data processing is handled on-chip and the linearized sensor die temperature Ta is made available in
memory.
The resolution of the calculated temperature is 0.02 ˚C. The sensor is factory calibrated for the full automotive
range (-40…+125 ˚C). In RAM cell 006h, 2DE4h corresponds to -38.2 ˚C (linearization output lower limit) and
4DC4h (19908d) corresponds to 125 ˚C. The conversions from RAM contend to real Ta is easy using the
following relation:
8.7.2 Object temperature To
The result has a resolution of 0.02 ˚C and is available in RAM. To is derived from RAM as:
Please note that 1LSB corresponds to 0,02Deg and the MSB bit is error flag (if “1” then error).
8.7.3 Calculation flow
The measurement, calculation and linearization are held by core, which executes a program form ROM.
After POR the chip is initialized with calibration data from EEPROM. During this phase the number of IR
sensors is selected and it is decided which temperature sensor will be used. Measurements, compensation
and linearization routines run in a closed loop afterwards.
3901090614
Rev 006
Ta
To
[
[
°
°
K
K
]
]
Example:
1. 0x0000 => -273,15˚C (no error) - min possible value returned by MLX90614
2. 0x0001 => -273.13˚C (no error)
3. 0x0002 => -273,11˚C (no error) and so on
4. 0x3AF7 => 28,75˚C (no error)
5. 0x7FFF => 382,19˚C (no error) - max possible value returned by MLX90614
The result is calculated by following expressions:
1. Convert it to decimal value i.e 0x3AF7 = 15095d
2. Divide by 50 (or multiply by 0,02) i.e. 15095/50=301,9K (result is in Kelvin)
3. Convert K -> ˚C i.e. 301,9-273,15=28,75˚C
=
=
Toreg
Tareg
×
×
. 0
. 0
02
02
, or 0.02 ° K / LSB.
, or 0.02 ° K / LSB.
V
ir
(
Ta
,
Page 26 of 49
To
)
=
A
.
(
To
4
Infra Red Thermometer in TO-39
−
Ta
4
)
,
Single and Dual Zone
September 30, 2010
Data Sheet