
Lucent Technologies Inc.
63
Data Sheet
June 1999
ORCA Series 2 FPGAs
Estimating Power Dissipation 
(continued)
P
CLK
 = [0.69 mW/MHz + (0.38 mW/MHz – Branch)
(20 Branches)
+ (0.022 mW/MHz – PFU) (150 PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(16 SMEM_PFUs)] [40 MHz] 
= 427 mW
P
TTL
= 20 x [2.2 mW + (0.17 mW/MHz x 20 MHz 
x 20%)] 
= 57 mW
P
CMOS
= 20 x [0.17 mW x 20 MHz x 20%] 
= 13 mW
P
OUT
 = 30 x [(30 pF + 8.8 pF) x (5.25)
2
 x 20 MHz 
x 20%] 
=128 mW
P
BID
= 16 x [(50 pF + 8.8 pF) x (5.25)
2
 x 20 MHz 
x 20%] 
= 104 mW
TOTAL
 = 1.50 W
OR2TxxA
The total operating power dissipated is estimated by 
summing the standby (I
DDSB
), internal, and external 
power dissipated. The internal and external power is 
the power consumed in the PLCs and PICs, respec-
tively. In general, the standby power is small and may 
be neglected. The total operating power is as follows:
P
T
 = 
Σ
 P
PLC
 + 
Σ
 P
PIC
The internal operating power is made up of two parts: 
clock generation and PFU output power. The PFU out-
put power can be estimated based upon the number of 
PFU outputs switching when driving an average fan-out 
of two:
P
PFU
 = 0.08 mW/MHz
For each PFU output that switches, 0.08 mW/MHz 
needs to be multiplied times the frequency (in MHz) 
that the output switches. Generally, this can be esti-
mated by using one-half the clock rate, multiplied by 
some activity factor; for example, 20%.
The power dissipated by the clock generation circuitry 
is based upon four parts: the fixed clock power, the 
power/clock branch row or column, the clock power dis-
sipated in each PFU that uses this particular clock, and 
the power from the subset of those PFUs that is config-
ured in either of the two synchronous modes (SSPM or 
SDPM). Therefore, the clock power can be calculated 
for the four parts using the following equations:
OR2T04A Clock Power
P
= [0.29 mW/MHz 
+ (0.10 mW/MHz – Branch) (# Branches)
+ (0.01 mW/MHz – PFU) (# PFUs)
+ (0.003 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2T04A clock power 
≈
 1.8 mW/MHz.
OR2T06A Clock Power
P
= [0.30 mW/MHz 
+ (0.11 mW/MHz – Branch) (# Branches)
+ (0.01 mW/MHz – PFU) (# PFUs)
+ (0.003 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2T06A clock power 
≈
 2.4 mW/MHz.
OR2T08A Clock Power
P
= [0.31 mW/MHz 
+ (0.12 mW/MHz – Branch) (# Branches)
+ (0.01 mW/MHz – PFU) (# PFUs)
+ (0.003 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2T08A clock power 
≈
 3.2 mW/MHz.
OR2T10A Clock Power
P
= [0.32 mW/MHz 
+ (0.14 mW/MHz – Branch) (# Branches)
+ (0.01 mW/MHz – PFU) (# PFUs)
+ (0.003 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2T10A clock power 
≈
 4.0 mW/MHz.
OR2T12A Clock Power
P
= [0.33 mW/MHz 
+ (0.15 mW/MHz – Branch) (# Branches)
+ (0.01 mW/MHz – PFU) (# PFUs)
+ (0.003 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2T12A clock power 
≈
 4.9 mW/MHz.