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7679H–CAN–08/08
AT90CAN32/64/128
26.4
Maximum Speed vs. V
CC
Maximum frequency is depending on V
CC
. As shown in Figure 26-2., the Maximum Frequency
vs. V
CC
curve is linear between 1.8V < V
CC
< 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
t
CLCX
Low Time
50
25
ns
t
CLCH
Rise Time
1.6
0.5
μ
s
t
CHCL
Fall Time
1.6
0.5
μ
s
Δ
t
CLCL
Change in period from one clock cycle
to the next
2
2
%
Table 26-1.
External Clock Drive (Continued)
Symbol
Parameter
V
CC
= 2.7 - 5.5V
V
CC
= 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
a
V
Vx
–
(
)
Fy
+
•
=
Voltage
b
F
Fy
–
(
)
Vx
+
•
=
Frequency
8
1.8
--------
3
2.7
–
(
)
8
+
•
9.33
=
=
Voltage
1.8
8
--------
8
8
–
(
)
2.7
+
•
2.7
=
=
Safe Operating Area
4.5V
2.7V
5.5V
8 MHz
16 MHz
Frequency
Voltage
