MLX90614_15 Datasheet, PDF (42/51 Pages) Melexis Microelectronic Systems – Single and Dual Zone Infra Red Thermometer in TO-39

MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
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 these phenomena and, in spite of the careful design of the MLX90614, it is recommended not to
subject the MLX90614 to heat transfer and especially transient conditions.
Upon power-up the MLX90614 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 to trigger on inappropriate levels, resulting
in unspecified operation and this is not recommended.
The MLX90614 is designed and calibrated to operate as a non contact thermometer in settled
conditions. Using the thermometer in a 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 MLX90614 additional improvement is possible by
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 MLX90614 implements Schmidt triggers on its 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 MLX90614 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.
In 12V powered systems SMBus usage is constrained because the SCL pin is used for the Zener
diode function. Applications where the supply is higher than 5V should use the PWM output or an external
regulator. Nevertheless, in the 12V powered applications MLX90614 can be programmed (configured and
customized) by forcing the Vdd to 5V externally and running the SMBus communication.
A sleep mode is available in the MLX90614Bxx. This mode is entered and exited via the SMBus
compatible 2-wire communication. On the other hand, the extended functionality of the SCL pin yields in
increased leakage current through that pin. As a result, this pin needs to be forced low in sleep mode and the
pull-up on the SCL line needs to be disabled in order to keep the overall power drain in sleep mode really small.
During sleep mode the sensor will not perform measurements.
The PWM pin is not designed for direct drive of inductive loads (such as electro-magnetic relays).
Some drivers need to be implemented for higher load, and auxiliary protection might be necessary even for light
but inductive loading.
It is possible to use the MLX90614 in applications, powered directly from the AC line (transformer less).
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 using the MLX90614 in that way.
Power dissipation within the package may affect performance in two ways: by heating the “ambient”
sensitive element significantly beyond the actual ambient temperature, as well as by causing gradients over the
package that will inherently cause thermal gradient over the cap. Loading the outputs also causes increased
power dissipation. In case of using the MLX90614Axx internal Zener voltage feature, the regulating external
transistor should also not cause heating of the TO39 package.
3901090614
Rev 009
Page 42 of 52
Data Sheet
June 29, 2015