Freescale Semiconductor DEMO9S08DZ60 Demo Board DEMO9S08DZ60 DEMO9S08DZ60 Hoja De Datos

Freescale Semiconductor

175

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

”.

•

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

 provides an approximate transfer function of the temperature sensor.

÷

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

. If V

TEMP

is

less than V

TEMP25

 the hot slope value is applied in

. 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

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.