Data Sheet

MLX90614 family
Single and Dual Zone
Infra Red Thermometer in TO-39
The different time intervals t
1
-t
3
have the following functions:
t
1
: Start buffer. During this time the signal is always high. t
1
= 0.125*T (T is the PWM period, refer to fig. 11).
t
2
: Valid Data Output Band, 0 to 1/2T. PWM output data resolution is 10 bit.
t
3
: Error band – information for fatal error in EEPROM (double error detected, not correctable). t
3
= 0.25 * T.
Therefore a PWM pulse train with a duty cycle of 0.875 will indicate a fatal error in EEPROM (for single PWM
format).
Example:
T
obj1
=> Config Reg[5:4] = 11’b
To
min
= 0°C => To
min
[EEPROM] = 100 * (to
min
+ 273.15) = 6AB3h
To
max
= +50°C => To
max
[EEPROM] = 100 * (to
max
+ 273.15) = 7E3Bh
Captured PWM high duration is 0.495*T => t
2
=(0.495 – 0.125)*T=0.370*T =>
measured object temperature = 2X0.370* (50°C -0°C)+0°C = +37.0°C.
8.5.2 Extended PWM format
The PWM format for extended PWM is shown in Figure 11. Note that with bits DUAL[5:1]>00h each period
will be outputted 2N+1 times, where N is the decimal value of the number written in DUAL[5:1] (DUAL[5:1]
=PWM control & clock [8:4] ), like shown on Figure 12.
Figure 12: Extended PWM format with DUAL[5:1] = 01h (2 repetitions for each data)
The temperature transmitted in Data 1 field can be calculated using the following equation:
()
111
2
1
*
2
TminTminTmax
T
t
Tout +
⎥
⎦
⎤
⎢
⎣
⎡
−=
For Data 2 field the equation is:
()
222
5
2
*
2
TminTminTmax
T
t
Tout +
⎥
⎦
⎤
⎢
⎣
⎡
−=
Where Tmin
1
, Tmax
1
, Tmin
2
and Tmax
2
are given in Table 9, t
2
=t
high1
-t
1
, and t
5
=t
high2
-t
4
.
Time bands are: t
1
=0.125*T, t
3
=0.25*T and t
4
=1.125*T. As shown in Figure 11, in extended PWM format the
period is twice the period for the single PWM format. All equations provided herein are given for the single
PWM period T. The EEPROM Error band signaling will be 43.75% duty cycle for Data1 and 93.75% for
Data2.
Note: EEPROM error signaling is implemented in automotive grade parts only.
Example:
Configuration: Ta : T
obj1
@ Data1 : Data2 => Config Reg[5:4] = 00b,
Ta
min
= -5°C => Ta
range
, L [EEPROM] = 100*(Ta
min
+38.2)/64 = 34h,
Ta
max
= +105°C => Ta
range
,H [EEPROM] = 100*(Ta
max
+38.2)/64 = E0h,
Ta
range
[EEPROM]=E034h
To
min
= 0°C => To
min
[EEPROM] = 100 * (To
min
+ 273.15) = 6AB3h
To
max
= +50°C => To
max
[EEPROM] = 100 * (To
max
+ 273.15) = 7E3Bh
Captured high durations are 0.13068*(2T) and 0.7475*(2T), where 2T is each captured PWM period. Time band t
4
is
provided for reliable determination between Data1 and Data2 data fields. Thus Data1 is represented by 0.13068*(2T) and
Data2 – by 0.7475*(2T), and the temperatures can be calculated as follows:
t
2
/T=(t
high1
/T)-0.125=0.13636 => Ta=+25.0°C,
t
5
/T=( t
high2
/T)-1.125=0.370 => T
obj1
=+37.0°C.
3901090614 Page 21 of 42 Data Sheet
Rev 004 30/Jul2008