Datasheet

187
8197C–AVR–05/11
ATtiny261A/461A/861A
19.3 Speed
The maximum operating frequency of the device is dependent on supply voltage, V
CC
. The rela-
tionship between supply voltage and maximum operating frequency is piecewise linear, as
shown in Figure 19-1.
Figure 19-1. Maximum Operating Frequency vs. Supply Voltage
19.4 Clock Characteristics
19.4.1 Accuracy of Calibrated Internal Oscillator
It is possible to manually calibrate the internal oscillator to be more accurate than default factory
calibration. Note that the oscillator frequency depends on temperature and voltage. Voltage and
temperature characteristics can be found in Figure 20-49 on page 223 and Figure 20-50 on
page 223.
Notes: 1. Accuracy of oscillator frequency at calibration point (fixed temperature and fixed voltage).
4 MHz
1.8V 5.5V
4.5V
20 MHz
2.7V
10 MHz
Table 19-2. Calibration Accuracy of Internal Oscillator
Calibration
Method Target Frequency V
CC
Temperature
Accuracy at given
voltage & temperature
(1)
Factory
Calibration
8.0 MHz 3V 25°C ±10%
User
Calibration
Fixed frequency
within:
7.3 - 8.1 MHz
Fixed voltage within:
1.8V - 5.5V
Fixed temperature
within:
-40°C to +85°C
±1%