MLX90614_15 Datasheet, PDF (22/51 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
8.5.1 Single PWM format
In single PWM output mode the settings for PWM1 data only are used. The temperature reading can be
calculated from the signal timing as:
( ) T_OUT
=  ^2t2 ×
^T
T_{O _ MAX}
− T_{O _ MIN}


+
T_O
_
MIN
where Tmin and Tmax are the corresponding rescale coefficients in EEPROM for the selected temperature
output (Ta, object temperature range is valid for both Tobj1 and Tobj2 as specified in the previous table) and T
is the PWM period. Tout is T_O1, T_O2 or T_a according to Config Register [5:4] settings.
The different time intervals t₁…t₄ have following meaning:
t₁: Start buffer. During this time the signal is always high. t₁ = 0.125s x T (where T is the PWM period,
please refer to Figure 14).
t₂: Valid Data Output Band, 0…1/2T. PWM output data resolution is 10 bit.
t₃: Error band – information for fatal error in EEPROM (double error detected, not correctable).
t₃ = 0.25s x T. Therefore a PWM pulse train with a duty cycle of 0.875 will indicate a fatal error in EEPROM (for
single PWM format). FE means Fatal Error.
Example:
Figure 15: PWM example single mode
( ) T_{O _ MIN} = 0°C T_{O _ MIN} (EEPROM ,0x01) = 100 × T_{O _ MIN} + 273.15 = 27315d = 0x6 AB3
( ) T_{O _ MAX} = 50°C T_{O _ MAX} (EEPROM ,0x00) = 100 × T_{O _ MAX} + 273.15 = 32315d = 0x7E3B
Captured PWM period is T = 1004µs
Captured high duration is t = 392 µs
Calculated duty cycle is:
D = ^t = ³⁹² = 0.3904 or 39.04%
T 1004
The temperature is calculated as follows:
T_O = 2 × (0.3904 − 0.125)× (50 − 0) + 0 = 2 × 0.2654 × 50 = 26.54°C
3901090614
Rev 009
Page 22 of 52
Data Sheet
June 29, 2015