PXS20RM Datasheet, PDF (1356/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Temperature Sensor (TSENS)
• Complementary to absolute temperature (CTAT) — V_TSENS decreases linearly with increasing
temperature
The mode of operation is controlled by the CTR1[TSENSOR_SEL] field in the ADC, as described in
Section 9.3.10.2, Conversion Timing Register 1 (CTR1).
50.5 Obtaining the device temperature using TSENS
In order to obtain the device temperature using TSENS, you must do the following:
• Extract the necessary TSENS calibration constants from the PXS20 test flash memory (see
Section 50.5.1, TSENS calibration constants)
• Measure V_TSENS in PTAT and CTAT modes
• Calculate the device temperature using the equations in Section 50.5.2, Equations for converting
TSENS voltage to device temperature
The need for the measurements in two different modes is driven by the fact that although the TSENS output
is linear in either mode, the intercept of the V_TSENS-T plot varies significantly based on the ADC reference
voltage. Performing the two measurements allows the resulting equations to be independent of this
reference voltage.
50.5.1 TSENS calibration constants
The equations needed to convert VTSENS to a device temperature depend on four calibration constants as
described in Table 50-1. These constants are determined during factory testing of the PXS20 and stored in
the PXS20 test flash memory as specified in Section 23.1.8, Test flash memory.
Table 50-1. TSENS calibration constants
Constant
P₁
P₂
C₁
C₂
Description
PTAT voltage (in V) measured at 150 C
PTAT voltage (in V) measured at -40 C
CTAT voltage (in V) measured at 150 C
CTAT voltage (in V) measured at -40 C
50.5.2 Equations for converting TSENS voltage to device temperature
In the equations below:
• V_P is the V_TSENS output in PTAT mode in V
• V_C is the V_TSENS output in CTAT mode in V
• P_n and C_n are the calibration constants described in Section 50.5.1, TSENS calibration constants
• T is the device temperature in C
First, calculate the constant factor K:
50-2
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor