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 MLX90614xxx, 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 MLX90614xxx 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 MLX90614xxx 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 MLX90614xxx 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.
Sleep mode is available in 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 power-down mode and the pull-up on
the SCL line needs to be disabled in order to keep the overall power drain in power-down really small.
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 MLX90614xxx 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 to use the MLX90614xxx 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
3901090614
Rev 003
Page 33 of 40
Data Sheet
03/Oct/2007
MELEXIS [ Melexis Microelectronic Systems ]
