Data Sheet

MCP3426/7/8
DS22226A-page 34 © 2009 Microchip Technology Inc.
Figure 6-7 shows an example of measuring both
pressure and temperature. The pressure is measured
by using NPP 301 (manufactured by GE NovaSensor),
and temperature is measured by a thermistor. The
pressure sensor output is 20 mV/V. This gives 100 mV
of full scale output for V
DD of 5V (sensor excitation
voltage). Equation 6-3 shows an example of calculating
the number of output code for the full scale output of the
NPP301.
EQUATION 6-3: EXPECTED NUMBER OF
OUTPUT CODE FOR
NPP301 PRESSURE
SENSOR
The thermistor temperature sensor can measure the
temperature range from -100°C to +300°C. The
resistance of the thermistor sensor decreases as
temperature increases (negative temperature
coefficient). As shown in Figure 6-7, the thermistor (R
2
)
forms a voltage divider with R
1
.
The thermistor sensor is simple to use and widely used
for the temperature measurement applications. It has
both linear and non-linear responses over temperature
range. R
1
is used to adjust the linear region of interest
for measurement.
Expected
log
2
100 mV
62.5μV
PGA
------------------
---------------------
⎝⎠
⎜⎟
⎜⎟
⎛⎞
= 10.6 bits for PGA = 1
= 11.6 bits for PGA = 2
= 12.6 bits for PGA = 4
= 13.6 bits for PGA = 8
Number of Output Code =
Where:
1 LSB = 62.5 µV with 16 Bit configuration.
1600 PGA•()ln
2()ln
----------------------------------------
⎝⎠
⎛⎞
=