MLX90821

Relative Pressure Sensor IC

Page 21 of 40

REV 004 – 4 MAR 2021

3901090821

NTC Temperature Linearization

The linearization of the NTC temperature signal is split up in several stages. A schematic overview of these steps

can be seen in Figure 11.

VDDA

Rs

Rntc

VDDA/2

ADC

Vdiv

ADC_raw[15:0]

Calibration

&

Compensation

LUT

ADC_ROM

=>

Tntc

ADC_comp[15:0]

3 or 4 points

MLX calibration

@ 3 temp

Figure 11: Block diagram NTC linearization

The complete system can be divided into 5 separate stages.

1. A resistor divider with internal resistor Rs is used to linearize Rntc into a voltage.

2. A fully differential amplifier with unity gain is used to drive the ADC.

3. The 16-bit ADC is being used to convert the analog resistor divider output voltage into a digital signal

called ADC_raw.

4. With the help of calibration data saved in EEPROM the microcontroller will perform a first compensation

on ADC_raw converting in to ADC_comp. This new value is targeted to be as close as possible to the value

ADC_ROM.

5. Finally a look up table (LUT) will be used to convert the ADC_ROM values into the Tntc value which is the

desired linearized NTC temperature.

The default optional NTC characteristic can be found in Table 14. When using an NTC which does not match the

coefficients described above, it is advised to contact Melexis.

The EEPROM coefficients which are used for the conversion from ADC_raw to ADC_comp are N0 to N3,

N0_Diff_Low to N3_Diff_Low, N0_Diff_High to N3_Diff_High and TEMP1 to TEMP3.