mlx90323 Melexis Company, mlx90323 Datasheet - Page 11

• Manufacturer Part Number: mlx90323
• Description: 4 ? 20 Ma Loop Sensor Interface With Signal Conditioning And Eeprom
• Manufacturer: Melexis Company

N_factor = Filter value set by the user (four LSB’s of byte 25 of EEPROM), range 0-6.
The filtered temperature value, Temp_f, is stored in RAM bytes 58 and 59. The data is a 10 bit value, left
justified in a 16 bit field.
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 (~72V/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
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)
3rd 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 => DAC_GAIN
If GNTC2,3,4 > 2047 => DAC_GAIN ↓
[V/V]
OFFSET
DAC_OFFSET (new value) ~ OF[9:0]+[OFTCi* dT]
3901090323
Rev 001
(
. 0
7.4
97
−
Parameters calculation
. 0
Temp_f(n+1) = new filtered temperature value
Temp_f(n) = previous filtered temperature value
Measured_temp = Value from temperature A to D
48
* )
GN
1023
[
Temp_f(n+1) = Temp_f(n) - [measured_temp - Temp_f(n)] [2
: 9
] 0
+
. 0
48
=
DAC
_
GAIN
Page 11 of 24
with Signal Conditioning and EEPROM
4 – 20 mA Loop Sensor Interface
n_factor
EEPROM table.
MLX90323
]
Data Sheet
March/08