MLX90616 Datasheet, PDF (25/36 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
8.8 Thermal relay
The MLX90616 can be configured to behave as a thermo relay with programmable threshold and hysteresis
on the PWM/SDA pin. The input for the comparator unit of the relay is the object temperature from sensor 1
The output of the MLX90616 is NOT a relay driver but a logical output which should be connected to a
relay driver if necessary.
The output driver is one and the same for PWM and Thermal relay.
In order to configure the MLX90616 to work as thermal relay two conditions must be met:
o Set bit TRPWMB high at address 002h in EEPROM
o Enable PWM output i.e. EN_PWM is set high
The PWM/SDA pin can be programmed as a push-pull or open drain NMOS (via bit PPODB in EEPROM
PWMCTRL), which can trigger an external device. The temperature threshold data is determined by
EEPROM at address 021h (Tomin) and the hysteresis at address 020h (To_max).
The logical state of the PWM/SDA pin is as follows:
PWM/SDA pin is high if T_obj1  threshold  hysteresis
PWM/SDA pin is low if T_obj1  threshold  hysteresis
“1”
hysteresis hysteresis
“0”
threshold
T
Figure 16: Thermal relay : “PWM” pin versus Tobj
The MLX90616 preserves its normal operation when configured as a thermal relay (PWM configuration and
specification applies as a general rule also for the thermal relay) and therefore it can be read using the
SMBus (entering the SMBus mode from both PWM and thermal relay configuration is the same).
For example, the MLX90616 can generate a wake-up alert for a system upon reaching a certain temperature
and then be read as a thermometer. A reset condition (enter and exit Sleep, for example) will be needed in
order to return to the thermal relay configuration.
Example:
Threshold = 5 °C(5 + 273.15)*50 = 13908  EEPROM 0x0001= 0x3654
Hysteresis = 1°C1*50=50  EEPROM 0x0000= 0x0032 (smallest possible hysteresis is 0,02°C or 0x0001)
PWM/SDA pin will be low at object temperature below 4 °C
PWM/SDA pin will be high at object temperature higher that 6 °C
3901090616
Rev 002
Page 25 of 36
Data Sheet
August 20, 2012