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MLX90308CCC Datasheet(PDF) 11 Page - Micro Electronics |
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MLX90308CCC Datasheet(HTML) 11 Page - Micro Electronics |
11 / 26 page ![]() MLX902xx Name of Sensor Rev Y.X 22/Aug/98 Page 11 MLX90308CCC Programmable Sensor Interface MLX90308CCC Programmable Sensor Interface Page 11 Rev 2.2 23/Oct/01 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 segment is performed the same way as for the gain. [mV/V] 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: 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. GAIN DAC GN _ 48 . 0 1023 ] 0 : 9 [ * ) 48 . 0 97 . 0 ( = + − OFFSET DAC OF _ 6 1023 ] 0 : 9 [ * ) 6 7 ( = − − − |
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