TN1180 Datasheet, PDF (1/9 Pages) STMicroelectronics – How to interpret pressure and temperature readings in pressure sensors

TN1180
Technical note
How to interpret pressure and temperature readings
in pressure sensors
By Tom Bocchino
Introduction
The purpose of this technical note is to provide a review of two's complement notation for ease of
design in pressure sensors and to guide the user in the interpretation of pressure and temperature
values in the device registers. MEMS pressure sensors measure absolute pressure (P) and
temperature (t) and store the values in two's complement registers which can be read via the
I²C or SPI host interface.
The pressure sensor stores pressure as a 24-bit word. Both values are stored as two's complement
integers as illustrated below.
Figure 1: Pressure sensor analog-to-digital data flow
Analog Domain
Digital Domain
P
Low Noise
Analog to
Digital Control
I²C
Analog Front
Digital
Signal Processing
End
Conversion
(DSP)
t
Sensors
and Bias
(AFE)
(ADC)
&
SPI
Register Bank
24-bit Pressure count
Two’s complement value
16-bit Temperature count
Two’s complement value
Addr(h)
Byte Description
28h PressureOut_XL (LSB)
29h PressureOut_L (MIDDLE)
2Ah PressureOut_H (MSB)
2Bh TemperatureOut_L (LSB)
2Ch TemperatureOut_H (MSB)
May 2014
DocID026298 Rev 1
1/9
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