Implementation
3.4 Temperature Sensor Measurement
The temperature sensor measurement is performed based on the methodology of an emulated ADC described in the application note, AN3266 “Getting Started with RS08”.
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MCU BOUNDARY
VDD
RVDD
4k7
7k5
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22nF |
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| 10k | |
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Figure 3-3. Emulated ADC Schematic
The schematic of the emulated ADC in this application is shown in Figure
With a 10kΩ temperature sensor and 7.5kΩ pullup resistor the ADC absolute dynamic range is from 0V to about 0.57 ⋅ VDD, i.e. about 2.85V. Timer clock is chosen to be eight times slower than the bus clock, the timer resolution becomes 2∝s. The RC charging profile follows EQ
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V = VDD⎜ | 1 – e RC⎟ | (EQ |
⎝ | ⎠ |
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Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
18 | Freescale Semiconductor |