HCS08 datasheet(96/198 Pages) NXP

96 / 198 page

Chapter 8 Analog-to-Digital Converter (ADC10V1)

MC9S08QD4 Series MCU Data Sheet, Rev. 6

Freescale Semiconductor

The RTI can be configured to cause a hardware trigger in MCU run, wait, and stop3.

8.1.1.4

Analog Pin Enables

The ADC on MC9S08QD4 contains only one analog pin enable register, APCTL1.

8.1.1.5

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

VBG the user can determine VDD. For value of bandgap voltage, see Appendix A.5, “DC

Characteristics”.

•

Convert the temperature sensor channel (AD26)

— By using the calculated value of VDD, convert the digital value of AD26 into a voltage, VTEMP

Equation 8-1 provides an approximate transfer function of the on-chip temperature sensor for VDD = 3.0V,

Temp = 25

°C, using the ADC at fADCK = 1.0 MHz and configured for long sample.

TempC = 25 – ((VTEMP – 1.3894) / ( 0.0033))

Eqn. 8-1

0.0017 is the uncalibrated voltage versus temperature slope in V/

°C. Uncalibrated accuracy of the

temperature sensor is approximately ± 12

°C, using Equation 8-1.

To improve accuracy the user must calibrate the bandgap voltage reference and temperature sensor.

Calibrating at 25

°C will improve accuracy to ± 4.5°C.

Calibration at 3 points, -40

°C, 25°C and 105°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 8-1 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.

8.1.1.6

Low-Power Mode Operation

The ADC is capable of running in stop3 mode but requires LVDSE in SPMSC1 to be set.

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