
62
Lucent Technologies Inc.
Data Sheet
June 1999
ORCA Series 2 FPGAs
Estimating Power Dissipation 
(continued)
OR2C06A Clock Power
P
= [0.63 mW/MHz 
+ (0.25 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C06A clock power 
≈
 5.3 mW/MHz.
OR2C08A Clock Power
P
= [0.65 mW/MHz 
+ (0.29 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C08A clock power 
≈
 6.6 mW/MHz.
OR2C10A Clock Power
P
= [0.66 mW/MHz 
+ (0.32 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C10A clock power 
≈
 8.6 mW/MHz.
OR2C12A Clock Power
P
= [0.68 mW/MHz 
+ (0.35 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C12A clock power 
≈
 10.5 mW/MHz.
OR2C15A Clock Power
P
= [0.69 mW/MHz 
+ (0.38 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C15A clock power 
≈
 12.7 mW/MHz.
OR2C26A Clock Power
P
= [0.73 mW/MHz 
+ (0.44 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C26A clock power 
≈
 17.8 mW/MHz.
OR2C40A Clock Power
P
= [0.77 mW/MHz 
+ (0.53 mW/MHz – Branch) (# Branches)
+ (0.022 mW/MHz – PFU) (# PFUs)
+ (0.006 mW/MHz – SMEM_PFU)
(# SMEM_PFUs)] fCLK
For a quick estimate, the worst-case (typical circuit) 
OR2C40A clock power 
≈
 26.6 mW/MHz.
The power dissipated in a PIC is the sum of the power 
dissipated in the four I/Os in the PIC. This consists of 
power dissipated by inputs and ac power dissipated by 
outputs. The power dissipated in each I/O depends on 
whether it is configured as an input, output, or input/
output. If an I/O is operating as an output, then there is 
a power dissipation component for P
IN
, as well as 
P
OUT
. This is because the output feeds back to the 
input. 
The power dissipated by a TTL input buffer is estimated 
as:
P
TTL
 = 2.2 mW + 0.17 mW/MHz
The power dissipated by an input buffer is estimated 
as:
P
CMOS
 = 0.17 mW/MHz
The ac power dissipation from an output or bidirec-
tional is estimated by the following:
P
OUT
 = (C
L
 + 8.8 pF) x V
DD
2
 x F Watts
where the unit for C
L
 is farads, and the unit for F is Hz.
As an example of estimating power dissipation, 
suppose that a fully utilized OR2C15A has an average 
of three outputs for each of the 400 PFUs, that all 
20 clock branches are used, that 150 of the 400 PFUs 
have FFs clocked at 40 MHz (16 of which are operating 
in a synchronous memory mode), and that the PFU 
outputs have an average activity factor of 20%. 
Twenty TTL-configured inputs, 20 CMOS-configured 
inputs, 32 outputs driving 30 pF loads, and 16 bidirec-
tional I/Os driving 50 pF loads are also generated from 
the 40 MHz clock with an average activity factor of 
20%. The worst-case (V
DD
 = 5.25 V) power dissipation 
is estimated as follows:
P
PFU
 = 400 x 3 (0.16 mW/MHz x 20 MHz x 20%) 
= 768 mW