MLX90616 Datasheet, PDF (8/36 Pages) Melexis Microelectronic Systems – Infra Red Thermometer in TO-39 for high temperature thermometer guns

8 Detailed description
8.1 Block diagram
81101
MLX90616ESF-HCA
Infra Red Thermometer in TO-39
for high temperature thermometer guns
OPA
ADC
DSP
PWM
t°
STATE MACHINE
90302
Voltage
Regulator
Figure 3: block diagram
8.2 Signal processing principle
The operation of the MLX90616 is controlled by an internal state machine, which controls the measurements
and calculations of the object and ambient temperatures and does the post-processing of the temperatures to
output them through the PWM output or the SMBus compatible interface.
The output of the IR sensors is amplified by a low noise low offset chopper amplifier with programmable gain,
converted by a Sigma Delta modulator to a single bit stream and fed to a powerful DSP for further
processing. The signal is treated by programmable (by means of EEPROM content) FIR and IIR low pass
filters for further reduction of the bandwidth of the input signal to achieve the desired noise performance and
refresh rate. The output of the IIR filter is the measurement result and is available in the internal RAM. 3
different cells are available: One for the on-board temperature sensor (on chip PTAT or PTC) and 2 for the IR
sensors.
Based on results of the above measurements, the corresponding ambient temperature Ta and object
temperature To are calculated. Both calculated temperatures have a resolution of 0.02 ˚C. The data for Ta
and To can be read in two ways: Reading RAM cells dedicated for this purpose via the 2-wire interface
(0.02°C resolution, fixed ranges), or through the PWM digital output (10 bit resolution, configurable range).
In the last step of the measurement cycle, the measured Ta and To are rescaled to the desired output
resolution of the PWM) and the recalculated data is loaded in the registers of the PWM state machine, which
creates a constant frequency with a duty cycle representing the measured data.
8.3 Block description
8.3.1 Amplifier
A low noise, low offset amplifier with programmable gain is used for amplifying the IR sensor voltage. By
carefully designing the input modulator and balanced input impedance, an offset below 0.5µV is achieved.
3901090616
Rev 002
Page 8 of 36
Data Sheet
August 20, 2012