MLX90614_15 Datasheet, PDF (30/51 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
8.8 Thermal relay
The MLX90614 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 MLX90614 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 MLX90614 to work as thermal relay two conditions must be met:
o Set bit TRPWMB high at address 0x02 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 0x21 (To_min) and the hysteresis at address 0x020 (To_max).
The logical state of the PWM/SDA pin is as follows:
PWM / SDA pin is high if T_O1 ≥ threshold + hysteresis
PWM / SDA pin is low if T_O1 ≤ threshold − hysteresis
“1”
hysteresis hysteresis
“0”
threshold
T
Figure 21: Thermal relay: “PWM” pin versus Tobj
The MLX90614 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 MLX90614 can generate a wake-up alert for a system upon reaching a certain
temperature and then be read as a thermometer. Reset conditions (enter and exit Sleep, for example) will be
needed in order to return to the thermal relay configuration.
Example:
Threshold = 5°C (EEPROM,0x01) = 100× (Threshold + 273.15) = 27815d = 0x6CA7
Hysteresis = 1°C (EEPROM,0x00) = 100× Hysteresis = 100d = 0x0064
Smallest possible hysteresis is 0,01°C or (EEPROM, 0x00 = 0x0001)
PWM / SDA pin will be set low at object temperature below 4°C
PWM / SDA pin will be set high at object temperature higher that 6°C
3901090614
Rev 009
Page 30 of 52
Data Sheet
June 29, 2015