MLX90614_15 Datasheet, PDF (20/51 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
8.4.9 MLX90614 SMBus specific remarks
The auxiliary functions of the SCL pin (zener diode) add undershoot to the clock pulse (5V devices
only) as shown in the picture below (see Figure 13). This undershoot is caused by the transient response of the
on-chip synthesized Zener diode. Typical duration of undershoot is approximately 15µs. An increased reactance
of the SCL line is likely to increase this effect. Undershoot does not affect the recognition of the SCL rising edge
by the MLX90914, but may affect proper operation of non-MLX90614 slaves on the same bus.
Figure 13: Undershoot of SCL line due to on chip synthesized Zener diode (5V versions only)
Continuous SMBus readings can introduce and error. As the SCL line inside TO39 package is passing
relatively close to the sensor input and error signal is induced to the sensor output. The manifestation of the
problem is wrong temperature readings. This is especially valid for narrow FOV devices. Possible solution is to
keep SDA and SCL line quiet for period longer than refresh rate and settling time defined by internal settings of
MLX90614 prior reading the temperature or switch to PWM signal and completely disconnect from SDA and
SCL line.
3901090614
Rev 009
Page 20 of 52
Data Sheet
June 29, 2015