MLX90308CAB Datasheet, PDF (11/26 Pages) List of Unclassifed Manufacturers – Programmable Sensor Interface

MLX90308CAB
Programmable Sensor Interface
Different Modes
Analog Mode
The parameters OF and GN represent, respectively,
offset correction and span control, while OFTCi and
GNTCi represent their temperature coefficients
(thermal zero shift and thermal span shift). After
reset, the firmware continuously calculates the offset
and gain DAC settings as follows: The EEPROM
holds parameters GN, OF, OFTCi and GNTCi, where
“i” is the gap number and can be 1 < i < 4. The
transfer function is described below.
Vout = FG * DAC_GAIN * CSGN[2:0] *
{Vin+DAC_OFFSET+CSOF}
Iout = FG * DAC_GAIN * CSGN[1:0] *
{Vin+DAC_OFFSET+CSOF} * 8.85mA/V
FG = Hardware Gain (~20V/V). Part of the hardware
design, and not changeable.
DAC_GAIN = GN[9:0] + [GNTCi * dT]
where
Temp_f = Filtered temperature (previously
described).
Ti= Temperature segment point I = 1,2, or 3.
GNTCi = Gain TC for a given temperature
segment i, GNTCiL and GNTCiH in
EEPROM table.
dT = Temperature change within the appropriate
gap. For the first gap dT = T1-Temp_f. For the
remaining gaps dT = Temp_f - T_(i-1), i = 2,3 or 4.
CSGN = Course Gain, part of byte 2 in
EEPROM.
GN[9:0] = Fixed Gain, bytes 3 and 17 in
EEPROM.
OFFSET
For the first temperature gap:
DAC_OFFSET = OF[9:0] + OFTCi *
(Ti – Temp_f).
For the second, third, and fourth temperature gaps:
DAC_OFFSET = OF + OFTCi * (Temp_f – Ti)
OF = Base Offset,
For the second temperature gap:
OF = OF[9:0]
For the third temperature gap:
OF = OF[9:0] + [OFTC2 * (T2-T1)]
For the fourth temperature gap:
OF = OF[9:0] + [OFTC2 * (T2-T1)]
+ [OFTC3 * (T3 – T2)]
CSOF = Coarse Offset, part of byte 2 in
EEPROM.
OF[9:0] = Fixed offset Bytes 4 and 17 in
EEPROM
Digital Mode
The MLX90308 firmware provides the capability of
digitally processing the sensor signal in addition to
the analog processing. This capability allows for
signal correction.
Signal Correction
While in digital mode the firmware can perform signal
correction. This is an adjustment to the output level
based on the input signal level. Adjustment
coefficients can be set for five different signal
ranges. The output is obtained by the following
formula:
Output = (Signal – Pi) * Pci + Poff where
Signal = input signal measurement;
Poff = Pressure ordinate
Pi = Pressure signal point (I = 2,3,4,5)
Pci = programmed coefficient.
The PCi coefficients are coded on 12 bits: one bit for
the sign, one for the unity, and the rest for the
decimals. The Pi are coded on 10 bits (0-3FFh) in
high-low order.
PNB_TNB: contains the number of signal points,
coded on the four MSB’s. The four LSB’s are
reserved for the number of temperature points. See
Table 4 and Table 5.
Compensation Trade-Offs
A compromise must be made between temperature
compensation and pressure correction. The
EEPROM space where the signal coefficients are
stored is shared with the temperature coefficients,
with the result that an EEPROM byte can be used
either for a temperature coefficient or for a signal
coefficient, but not both. Table 6 presents the
possibilities among the maximum number of
temperature gaps and the maximum number of
signal gaps.
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