
RadTolerant FPGAs
v3.1
1-9
Active Power Component
Power dissipation in CMOS devices is usually dominated
by
the
active
(dynamic)
power
dissipation.
This
component is frequency-dependent, a function of the
logic and the external I/O. Active power dissipation
results from charging internal chip capacitances of the
interconnect, unprogrammed antifuses, module inputs,
and module outputs, plus external capacitance due to PC
board traces 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.
Equivalent Capacitance
The power dissipated by a CMOS circuit can be expressed
Power (uW) = CEQ * VCC
2 * F
EQ 1-4
where:
Equivalent capacitance is calculated by measuring ICCactive
at a specified frequency and voltage for each circuit
component of interest. Measurements are made over a
range of frequencies at a fixed value of VCC. Equivalent
capacitance is frequency-independent, so the results can
be used over a wide range of operating conditions.
Equivalent capacitance values are shown in
Table 1-7.CEQ = Equivalent capacitance in pF
VCC = Power supply in volts (V)
F
= Switching frequency in MHz
Table 1-7 CEQ Values for Actel FPGAs
RT1020,
A1020B
RT1280A,
A1280A
RT1425A, A1425A, RT1460A,
A1460A, RT14100A, A14100A
Modules (CEQM)3.7
5.8
6.7
Input Buffers (CEQI)
22.1
12.9
7.2
Output Buffers (CEQO)
32.1
23.8
10.4
Routed Array Clock Buffer Loads (CEQCR)4.6
3.9
1.6
Dedicated Clock Buffer Loads (CEQCD)
n/a
0.7
I/O Clock Buffer Loads (CEQCI)
n/a
0.9