A1280A Actel, A1280A Datasheet - Page 6

• Manufacturer Part Number: A1280A
• Description: (A1225A - A1280A) FPGAs
• Manufacturer: Actel

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and load device inputs. An additional component of the
active power dissipation is the totem-pole current in CMOS
transistor pairs. The net effect can be associated with an
equivalent capacitance that can be combined with
frequency and voltage to represent active power dissipation.
E quiv al ent C apac it ance
The power dissipated by a CMOS circuit can be expressed by
the Equation 1.
Where:
C
V
F is the switching frequency in MHz.
Equivalent capacitance is calculated by measuring ICC
active at a specified frequency and voltage for each circuit
component of interest. Measurements have been made over
a range of frequencies at a fixed value of VCC. Equivalent
capacitance is frequency independent so that the results
may be used over a wide range of operating conditions.
Equivalent capacitance values are shown below.
C
Modules (C
Input Buffers (C
Output Buffers (C
Routed Array Clock Buffer Loads (C
To calculate the active power dissipated from the complete
design, the switching frequency of each part of the logic
must be known. Equation 2 shows a piece-wise linear
summation over all components.
Power = V
+ (p * (C
f
f
+ (r
Where:
6
q1
q2
m
n
p
q1
q2
r
CC
EQ
1
E Q
4
)
)
routed_Clk1
routed_Clk2
2
U
is the power supply in volts.
is the equivalent capacitance expressed in pF.
* f
Va lues f or Ac tel F PG A s
.com
q2
= Number of logic modules switching at fm
= Number of input buffers switching at fn
= Number of output buffers switching at fp
= Fixed capacitance due to first routed array
= Number of clock loads on the first routed array
= Number of clock loads on the second routed
EQO
)
CC
routed_Clk2
EQM
clock
array clock
clock
2
+ C
Power ( µ W) = C
* [(m * C
+ (r
)
EQI
L
) * f
EQO
1
)
* f
]
p
)
q1
)
EQM
outputs
)
routed_Clk1
* f
m
+ 0.5 * (q
EQ
)
modules
* V
+ 0.5 * (q
EQCR
CC
2
+(n * C
1
* F
)
* C
EQCR
2
* C
EQI
12.9
5.8
23.8
3.9
*
EQCR
* f
n
)
inputs
*
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(1)
(2)
v4.0
Fi xed Ca paci ta nce Val ues fo r Act el FP GA s
(pF )
Device Type
A1225A
A1240A
A1280A
D et erm i nin g A ve ra ge S wi t chi ng F re quenc y
To determine the switching frequency for a design, you must
have a detailed understanding of the data input values to
the circuit. The following guidelines are meant to represent
worst-case scenarios so that they can be generally used to
predict the upper limits of power dissipation. These
guidelines are as follows:
r
C
C
C
C
C
f
f
f
f
f
Logic Modules (m)
Inputs switching (n)
Outputs switching (p)
First routed array clock loads (q
Second routed array clock loads (q
Load capacitance (C
Average logic module switching rate (f
Average input switching rate (f
Average output switching rate (f
Average first routed array clock rate (f
Average second routed array clock rate
(f
m
n
p
q1
q2
2
EQM
EQI
EQO
EQCR
L
q2
)
= Fixed capacitance due to second routed array
= Equivalent capacitance of logic modules in pF
= Equivalent capacitance of input buffers in pF
= Equivalent capacitance of output buffers in pF
= Equivalent capacitance of routed array clock in
= Output lead capacitance in pF
= Average logic module switching rate in MHz
= Average input buffer switching rate in MHz
= Average output buffer switching rate in MHz
= Average first routed array clock rate in MHz
= Average second routed array clock rate in MHz
clock
pF
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r1
routed_Clk1
106
134
168
L
)
n
A C T
1
)
p
)
)
2
)
™
106.0
134.2
167.8
r2
routed_Clk2
m
q1
2 F a m il y F P GA s
)
) F
80% of modules
# inputs/4
# outputs/4
40%of
sequential
modules
40%of
sequential
modules
35 pF
F/10
F/5
F/10
F/2