EVB90615 Datasheet, PDF (24/30 Pages) Melexis Microelectronic Systems – Infra Red Thermometer

MLX90615
Infra Red Thermometer
12 Application Comments
Significant contamination at the optical input side (sensor filter) might cause unknown additional
filtering/distortion of the optical signal and therefore result in unspecified errors.
IR sensors are inherently susceptible to errors caused by thermal gradients. There are physical reasons for
that phenomena and, in spite of the careful design of the MLX90615, it is recommended not to subject the
MLX90615 to heat transfer and especially transient conditions.
Upon power-up the MLX90615 passes embedded checking and calibration routines. During these routines
the output is not defined and it is recommended to wait for the specified POR time before reading the module.
Very slow power-up may cause the embedded POR circuitry trigger on inappropriate levels, resulting in
unspecified operation and is not recommended.
The MLX90615 is designed and calibrated to operate as a non contact thermometer in settled conditions.
Using the module in very different way will result in unknown results.
Capacitive loading on a SMBus can degrade the communication. Some improvement is possible with use
of current sources compared to resistors in pull-up circuitry. Further improvement is possible with specialized
commercially available bus accelerators. With the MLX90615 additional improvement is possible with
increasing the pull-up current (decreasing the pull-up resistor values). Input levels for SMBus compatible
mode have higher overall tolerance than the SMBus specification, but the output low level is rather low even
with the high-power SMBus specification for pull-up currents. Another option might be to go for a slower
communication (clock speed), as the MLX90615 implements Schmidt triggers on it’s inputs in SMBus
compatible mode and is therefore not really sensitive to rise time of the bus (it is more likely the rise time to
be an issue than the fall time, as far as the SMBus systems are open drain with pull-up).
For ESD protection there are clamp diodes between the Vss and Vdd and each of the other pins. This
means that the MLX90615 might draw current from a bus in case the SCL and/or SDA is connected and the
Vdd is lower than the bus pull-ups’ voltage.
It is possible to use the MLX90615 in applications, powered directly from the AC line (trasformerless). In such
cases it is very important not to forget that the metal package of the sensor is not isolated and therefore
may occur to be connected to that line, too. Melexis can not be responsible for any application like this and
highly recommends not to use the MLX90615 in that way.
Check www.melexis.com for most current application notes about MLX90615.
3901090615
Rev 001
Page 24 of 30
Data Sheet
28/Aug/2008