eX Family FPGAs
Revision 10
1-19
Power Dissipation
Power consumption for eX devices can be divided into two components: static and dynamic.
Static Power Component
The power due to standby current is typically a small component of the overall power. Typical standby
eX128 at 3.3 V VCCI is:
ICC * VCCA = 795 A x 2.5 V = 1.99 mW
Dynamic Power Component
Power dissipation in CMOS devices is usually dominated by the dynamic power dissipation. This
component is frequency-dependent and a function of the logic and the external I/O. Dynamic power
dissipation results from charging internal chip capacitance due to PC board traces and load device
inputs. An additional component of the dynamic power dissipation is the totem pole current in the CMOS
transistor pairs. The net effect can be associated with an equivalent capacitance that can be combined
with frequency and voltage to represent dynamic power dissipation.
Dynamic power dissipation = CEQ * VCCA2 x F
where:
Equivalent capacitance is calculated by measuring ICCA 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 the results can be used over a wide
range of operating conditions. Equivalent capacitance values are shown below.
CEQ Values for eX Devices
The variable and fixed capacitance of other device components must also be taken into account when
estimating the dynamic power dissipation.
Table 1-12 shows the capacitance of the clock components of eX devices.
CEQ = Equivalent capacitance
F
= switching frequency
Combinatorial modules (Ceqcm)
1.70 pF
Sequential modules (Ceqsm)
1.70 pF
Input buffers (Ceqi)
1.30 pF
Output buffers (Ceqo)
7.40 pF
Routed array clocks (Ceqcr)
1.05 pF
Table 1-12 Capacitance of Clock Components of eX Devices
eX64
eX128
eX256
Dedicated array clock – variable (Ceqhv)
0.85 pF
Dedicated array clock – fixed (Ceqhf)
18.00 pF
20.00 pF
25.00 pF
Routed array clock A (r1)
23.00 pF
28.00 pF
35.00 pF
Routed array clock B (r2)
23.00 pF
28.00 pF
35.00 pF