MC9S08SH32CWL Datasheet, PDF (123/328 Pages) Freescale Semiconductor, Inc – MC9S08SH32 Series Features

Chapter 9 Analog-to-Digital Converter (S08ADCV1)
Equation 9-1 provides an approximate transfer function of the temperature sensor.
Temp = 25 - ((V_TEMP -V_TEMP25) ÷ m)
Eqn. 9-1
where:
— V_TEMP is the voltage of the temperature sensor channel at the ambient temperature.
— V_TEMP25 is the voltage of the temperature sensor channel at 25°C.
— m is the hot or cold voltage versus temperature slope in V/°C.
For temperature calculations, use the V_TEMP25 and m values from the ADC Electricals table.
In application code, the user reads the temperature sensor channel, calculates V_TEMP, and compares to
V_TEMP25. If V_TEMP is greater than V_TEMP25 the cold slope value is applied in Equation 9-1. If V_TEMP is
less than V_TEMP25 the hot slope value is applied in Equation 9-1. To improve accuracy the user should
calibrate the bandgap voltage reference and temperature sensor.
Calibrating at 25°C will improve accuracy to ± 4.5°C.
Calibration at three points, -40°C, 25°C, and 125°C will improve accuracy to ± 2.5°C. Once calibration
has been completed, the user will need to calculate the slope for both hot and cold. In application code, the
user would then calculate the temperature using Equation 9-1 as detailed above and then determine if the
temperature is above or below 25°C. Once determined if the temperature is above or below 25°C, the user
can recalculate the temperature using the hot or cold slope value obtained during calibration.
MC9S08SH32 Series Data Sheet, Rev. 2
Freescale Semiconductor
123
PRELIMINARY