MLX90616 Datasheet, PDF (31/36 Pages) Melexis Microelectronic Systems – Infra Red Thermometer in TO-39 for high temperature thermometer guns

MLX90616ESF-HCA
Infra Red Thermometer in TO-39
for high temperature thermometer guns
11.4 Thermal alert / thermostat
+5V
- _D1
+ ^{Alert dev ice}
2
PWM
SDA
Vdd
3
SCL ¹
Vz
C1 U1
0.1uF
Vss
4 ^MLX90614Axx
+3.3V
R1 R2
2
PWM
SDA
Vdd
3
SCL ¹
Vz
C1 U1
0.1uF
Vss
4 ^MLX90614Bxx
SMBus
U1
Vdd
SDA
SCL
GND
MCU
+24V
R1
R2
Q1
2
PWM
SDA
Vdd
3
SCL ¹
Vz
C2
C3
Vss
4
C*
U2
10uF
0.1uF
AC line
Figure 24: Thermal alert/thermostat applications of MLX90616
The MLX90616 can be configured in EEPROM to operate as a thermal relay. A non contact freezing or
boiling prevention with 1 mA quiescent current can be built with two components only – the MLX90616 and a
capacitor. The PWM/SDA pin can be programmed as a push-pull or open drain NMOS, which can trigger an
external device, such as a relay (refer to electrical specifications for load capability), buzzer, RF transmitter or
a LED. This feature allows very simple thermostats to be built without the need of any MCU and zero design
overhead required for firmware development. In conjunction with a MCU, this function can operate as a
system alert that wakes up the MCU. Both object temperature and sensor die temperature can also be read
in this configuration.
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 MLX90616xxx, it is recommended not to subject
the MLX90616 to heat transfer and especially transient conditions.
Upon power-up the MLX90616 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 MLX90616xxx 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 MLX90616xxx 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 MLX90616xxx implements Schmitt 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 will
be an issue than the fall time, as far as the SMBus systems are open drain with pull-up).
3901090616
Rev 002
Page 31 of 36
Data Sheet
August 20, 2012