mlx90314 Melexis Company, mlx90314 Datasheet - Page 11

• Manufacturer Part Number: mlx90314
• Description: Programmable Sensor Interface
• Manufacturer: Melexis Company

Different Modes
Analog Mode
The parameters OF and GN represent, respectively,
offset correction and span control, while OFTCi and
GNTCi
(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
{Vin+DAC_OFFSET+CSOF}
Iout = FG * DAC_GAIN * CSGN[1:0] *
{Vin+DAC_OFFSET+CSOF} * 8.85mA/V
FG = Hardware Gain (~72V/V). Part of the hardware
CSGN = Course Gain, part of byte 2 in EEPROM.
CSOF = Coarse Offset, part of byte 2 in
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
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 *
3th gap: DAC_GAIN = DAC_GAIN2 + GNTC3 *
4th gap: DAC_GAIN = DAC_GAIN3 + GNTC4 *
Where:
Temp_f = Filtered temp. (previously described).
If GNTC1 > 2047 => DAC_GAIN
If GNTC2,3,4 > 2047 => DAC_GAIN
[V/V]
MLX902xx Name of Sensor Rev Y.X 22/Aug/98
3901090314
Rev 007
(
(Temp_f2 – T1)
(Temp_f3 – T2)
(Temp_f4 – T3)
. 0
EEPROM.
97
design, and not changeable.
segment I. GNTCiL and GNTCiH in
EEPROM table.
. 0
=
represent
48
* )
FG
GN
1023
*
[
: 9
their
] 0
DAC_GAIN
. 0
48
temperature
DAC
*
_
CSGN[2:0]
GAIN
coefficients
Page 11
*
Page 11
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
dT = Temp. change within the appropriate gap.
Calculation of the offset for a given temperature seg-
ment is performed the same way as for the gain.
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
coefficients can be set for five different signal ranges.
The output is obtained by the following formula:
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.
. 1 (
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.
Programmable Sensor Interface
83
segment I. OFTCiL and OFTCiH in
EEPROM table.
. 1
on
57
* )
the
OF
1023
[
: 9
input
] 0
. 1
57
signal
DAC
MLX90314
_
level.
OFFSET
Adjustment
[mV/V]
Nov/04