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7679H–CAN–08/08
AT90CAN32/64/128
26.4
Maximum Speed vs. V
CC
Maximum frequency is depending on V
vs. V
CC curve is linear between 1.8V < VCC < 4.5V. To calculate the maximum frequency at a
given voltage in this interval, use this equation:
To calculate required voltage for a given frequency, use this equation:
At 3 Volt, this gives:
Thus, when V
CC = 3V, maximum frequency will be 9.33 MHz.
At 8 MHz this gives:
Thus, a maximum frequency of 8 MHz requires V
CC = 2.7V.
Figure 26-2. Maximum Frequency vs. V
CC, AT90CAN32/64/128
tCLCX
Low Time
50
25
ns
tCLCH
Rise Time
1.6
0.5
μs
tCHCL
Fall Time
1.6
0.5
μs
Δt
CLCL
Change in period from one clock cycle
to the next
22
%
Table 26-1.
External Clock Drive (Continued)
Symbol
Parameter
VCC = 2.7 - 5.5V
VCC = 4.5 - 5.5V
Units
Min.
Max.
Min.
Max.
Table 26-2.
Constants used to calculate maximum speed vs. V
CC
Voltage and Frequency range
a
b
Vx
Fy
2.7 < VCC < 4.5 or 8 < Frequency < 16
8/1.8
1.8/8
2.7
8
Frequency
aV
Vx
–
() Fy
+
=
Voltage
bF
Fy
–
() Vx
+
=
Frequency
8
1.8
--------
32.7
–
() 8
+
9.33
==
Voltage
1.8
8
--------
88
–
() 2.7
+
2.7
==
Safe Operating Area
4.5V
2.7V
5.5V
8 MHz
16 MHz
Frequency
Voltage