EX128-PTQG100 Datasheet, PDF (20/49 Pages) Actel Corporation – eX Family FPGAs

eX Family FPGAs
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 current
for eX devices is listed in the Table 1-11 on page 1-13. For
example, the typical static power for eX128 at 3.3 V V_CCI
is:
I_CC * V_CCA = 795 µA 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 * V_CCA2 x F
where:
CEQ = Equivalent capacitance
F = switching frequency
Equivalent capacitance is calculated by measuring I_CCA 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 V_CC.
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
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
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.
Table 1-12 • Capacitance of Clock Components of eX
Devices
eX64 eX128 eX256
Dedicated array clock – 0.85 pF 0.85 pF 0.85 pF
variable (Ceqhv)
Dedicated array clock – fixed 18.00 pF 20.00 pF 25.00 pF
(Ceqhf)
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
The estimation of the dynamic power dissipation is a
piece-wise linear summation of the power dissipation of
each component.
Dynamic power dissipation
= V_CCA2 * [(m_c * C_eqcm * fm_C)_{Comb Modules} + (m_s * C_eqsm *
fm_S)_{Seq Modules} + (n * C_eqi * fn)_{Input Buffers} + (0.5 * (q1 *
C_eqcr * fq1) + (r1 * fq1))_RCLKA + (0.5 * (q2 * C_eqcr * fq2) +
(r2 * fq2))_RCLKB + (0.5 * (s1 * C_eqhv * fs1)+(C_eqhf *
fs1))_HCLK] + V_CCI2 * [(p * (C_eqo + C_L) * fp)_{Output Buffers}]
where:
m_c = Number of combinatorial cells switching at
frequency fm, typically 20% of C-cells
m_s = Number of sequential cells switching at
frequency fm, typically 20% of R-cells
n = Number of input buffers switching at
frequency fn, typically number of inputs / 4
p = Number of output buffers switching at
frequency fp, typically number of outputs / 4
q1 = Number of R-cells driven by routed array
clock A
q2 = Number of R-cells driven by routed array
clock B
r1 = Fixed capacitance due to routed array clock A
r2 = Fixed capacitance due to routed array clock B
s1 = Number of R-cells driven by dedicated array
clock
C_eqcm = Equivalent capacitance of combinatorial
modules
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