MLX90323 Datasheet, PDF(14/25 Page) Melexis Microelectronic Systems – 4 – 20 mA Loop Sensor Interface with Signal Conditioning and EEPROM

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MLX90323 Datasheet, PDF (14/25 Pages) Melexis Microelectronic Systems – 4 – 20 mA Loop Sensor Interface with Signal Conditioning and EEPROM

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MLX90323

4 â 20 mA Loop Sensor Interface

with Signal Conditioning and EEPROM

GNTC

The GNTC values are the gain temperature compensation values for each of the four temperature gaps,

GNCT1, GNTC2, GNTC3, and GNTC4. These values are used to adjust the signal up or down based on the

relative temperature within a particular gap. Mathematically this is represented by the following equation:

DAC_GAIN = CSGN * {GN[9:0] + [GNTCi *âTi]}

Where:

âTi = (T1 â temp_f) for gap 1;

âTi = (temp_f â Ti-1) for gaps 2,3,and 4;

Temp_f = Filtered temperature;

DAC_GAIN = The digital value that adjusts the gain on the gain amplifier;

Ti = Temperature segment point i = 2, 3, or 4;

GNTCi = Gain TC for a given temperature segment I;

CSGN = Course Gain;

GN[9:0] = Fixed Gain (doesnât change with temperature).

The GNTC and OFTC values are 12 bit fixed point signed numbers (see table 4). That means that the most

significant bit is a sign bit. The next bit is one or zero (whole number). The remaining 10 bits are to the right

of the decimal point. This gives the variable the range of â1.9990234 to +1.9990234. The table below shows

how the fixed point numbers are represented as the binary number progresses from 0 to 4095.

OFTC

The OFTC values are the offset temperature compensation values for each of the four temperature gaps,

OFCT1, OFTC2, OFTC3, and OFTC4. These values are used to adjust the signalâs offset up or down based

on the relative temperature within a particular gap. The offset adjustment is additive from one gap to the

next. That is the offset adjustment for the fourth gap is added to the total offset adjustment of the third gap

which is also added to the total offset adjustment of the second gap. Mathematically this is represented by

the following equation:

For the first temperature gap:

DAC_OFFSET = OF[9:0] + OFTCi * (T1 â Temp_f)

For the second temperature gap:

DAC_OFFSET =OF[9:0] + OFTC2 * (Temp_f â T2)

For the third temperature gap:

DAC_OFFSET = OF[9:0] + [OFTC2 * (T2-T1)] + OFTC3 * (Temp_f â T3)

For the fourth temperature gap:

DAC_OFFSET =OF[9:0] + [OFTC2 * (T2-T1)] + [OFTC3 * (T3 â T2)] + OFTC4 * (Temp_f â T4),

Where OF[9:0] = Fixed offset

3901090323

Rev 003

Page 14 of 25

Data Sheet

Feb/12

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