MLX90314 Datasheet, PDF (11/26 Pages) List of Unclassifed Manufacturers – Programmable Sensor Interface

MLX90314AB
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.
CSGN = Course Gain, part of byte 2 in EEPROM.
CSOF = Coarse Offset, part of byte 2 in
EEPROM.
GAIN
DAC_GAIN (new value) ~ GN[9:0] + [GNTCi * dT]
GN[9:0] = Fixed Gain, bytes 3 and 17 in EEPROM.
GNTCi = Gain TC for a given temperature
segment I. GNTCiL and GNTCiH in
EEPROM table.
dT = Temp. change within the appropriate gap.
How to calculate gain in the first temp. gap?:
DAC_GAIN = GN[9:0] - GNTC1 * (T1 – Temp_f1)
How to calculate gain in the other temp. gaps?:
2nd gap:DAC_GAIN = GN[9:0] + GNTC2 *
(Temp_f2 – T1)
3th gap: DAC_GAIN = DAC_GAIN2 + GNTC3 *
(Temp_f3 – T2)
4th gap: DAC_GAIN = DAC_GAIN3 + GNTC4 *
(Temp_f4 – T3)
Where:
Temp_f = Filtered temp. (previously described).
If GNTC1 > 2047
If GNTC2,3,4 > 2047
=> DAC_GAIN ↑
=> DAC_GAIN ↓
(0.97 − 0.48) * ^{GN[9 : 0]} + 0.48 = DAC _ GAIN ^[V/V]
1023
OFFSET
DAC_OFFSET (new value) ~ OF[9:0]+[OFTCi* dT]
OF[9:0] = Fixed Gain, bytes 4 and 17 in EEPROM.
OFTCi = Offset for a given temperature
segment I. OFTCiL and OFTCiH in
EEPROM table.
dT = Temp. change within the appropriate gap.
Calculation of the offset for a given temperature
segment is performed the same way as for the gain.
(1.83− −1.57)* ^{OF[9 : 0]} −1.57 = DAC _ OFFSET [mV/V]
1023
Digital Mode
The MLX90314 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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