Rainbow Electronics ATmega64M1 - Manual (Page 239)

239
8209A–AVR–08/09
ATmega16M1/32M1/64M1
The measured voltage has a linear relationship to the temperature as described in Table 22-3 on
page 239 . The voltage sensitivity is approximately 1 mV/ ° C and the accuracy of the temperature
measurement is +/- 10°C after bandgap calibration.
The values described in Table 22-3 on page 239 are typical values. However, due to the process
variation the temperature sensor output voltage varies from one chip to another. To be capable
of achieving more accurate results, the temperature measurement can be calibrated in the appli-
cation software.
22.8.1 User Calibration
The software calibration requires that a calibration value is measured and stored in a register or
EEPROM for each chip. The software calibration can be done utilizing the formula:
T = { [ (ADCH << 8) | ADCL ] - T
OS
} / k
where ADCH & ADCL are the ADC data registers, k is a fixed coefficient and T
OS
is the temper-
ature sensor offset value determined and stored into EEPROM.
22.8.2 Manufacturing Calibration
One can also use the calibration values available in the signature row See “Reading the Signa-
ture Row from Software” on page 281.
The calibration values are determined from values measured during test at room temperature
which is approximatively +25°C and during test at hot temperature which is approximatively
+85°C.
The temperature in Celsius degrees can be calculated utilizing the formula:
T = { [ (ADCH << 8) | ADCL ] *TSGAIN } +TSOFFSET-273
Where:
a. ADCH & ADCL are the ADC data registers,
b. TSGAIN is the temperature sensor gain (constant 1, or unsigned fixed point num-
ber, 0x80 = decimal 1.0)
c. TSOFFSET is the temperature sensor offset correction term (2. complement
signed byte)
22.9 Amplifier
The ATmega16M1/32M1/64M1 features three differential amplified channels with programmable
5, 10, 20, and 40 gain stage.
Because the amplifiers are switching capacitor amplifiers, they need to be clocked by a synchro-
nization signal called in this document the amplifier synchronization clock. To ensure an
accurate result, the amplifier input needs to have a quite stable input value during at least 4
Amplifier synchronization clock periods.
To ensure an accurate result, the amplifier input needs to have a quite stable input value at the
sampling point during at least 4 amplifier synchronization clock periods.
Table 22-3. Temperature vs. Sensor Output Voltage (Typical Case)
Temperature /
°C
-40
°C
+25
°C
+85
°C
Voltage / mV 600 mV 762 mv TBD mV