MLX90308LDF データシートの表示（PDF） - Melexis Microelectronic Systems

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MLX90308LDF

Programmable Sensor Interface

Melexis Microelectronic Systems  

MLX90308CCC

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 => DAC_GAIN ↑

If GNTC2,3,4 > 2047 => DAC_GAIN ↓

[V/V]

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 seg-

ment is performed the same way as for the gain.

(7 − −6)* OF[9 : 0] − 6 = DAC _ OFFSET [mV/V]

1023

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:

1st gap: Output = (Signal ) * PC1 + Poff

Where:

Signal = input signal measurement;

Poff = Pressure ordinate = P1

PC1 = programmed coefficient first gap.

Following gaps:

Gap i: Output = (Signal – Pi) * PCi + Poff_i

Where

Signal = input signal measurement;

Poff_i = Pressure ordinate (i = 2,3,4,5)

Pi = Pressure signal point (i = 2,3,4,5)

PCi = programmed coefficient first gap (i = 2,3,4,5).

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.

(0.97 − 0.48) * GN[9 : 0] + 0.48 = DAC _ GAIN

1023

M39L0X190029x0x3N08ame of Sensor Rev Y.X 22/Aug/98

Rev 004

Page P11age 11

Aug/02

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