MC9S08DZ60MLF Datasheet, PDF (175/416 Pages) Freescale Semiconductor, Inc – MC9S08DZ60 Series Features

Chapter 10 Analog-to-Digital Converter (S08ADC12V1)
10.1.5 Temperature Sensor
To use the on-chip temperature sensor, the user must perform the following:
• Configure ADC for long sample with a maximum of 1 MHz clock
• Convert the bandgap voltage reference channel (AD27)
— By converting the digital value of the bandgap voltage reference channel using the value of
V_BG the user can determine V_DD. For value of bandgap voltage, see Section A.6, “DC
Characteristics”.
• Convert the temperature sensor channel (AD26)
— By using the calculated value of V_DD, convert the digital value of AD26 into a voltage, V_TEMP
Equation 10-1 provides an approximate transfer function of the temperature sensor.
Temp = 25 - ((V_TEMP -V_TEMP25) ÷ m)
Eqn. 10-1
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 10-1. If V_TEMP is
less than V_TEMP25 the hot slope value is applied in Equation 10-1. 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 10-1 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.
MC9S08DZ60 Series Data Sheet, Rev. 4
Freescale Semiconductor
175