Datasheet

SN74ALVC7804
512 × 18
FIRST-IN, FIRST-OUT MEMORY
SCAS432 – JANUARY 1995
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
0
20
40
60
80
100
120
140
0 102030405060708090
I – Supply Current – mA
CC(f)
SUPPLY CURRENT
vs
CLOCK FREQUENCY
f
clock
– Clock Frequency – MHz
V
CC
= 3.6 V
V
CC
= 3.3 V
V
CC
= 3 V
f
data
= 1/2 f
clock
T
A
= 75°C
C
L
= 0 pF
Figure 4
calculating power dissipation
With I
CC(f)
taken from Figure 4, the dynamic power (P
d
), based on all data outputs changing states on each read,
can be calculated by using:
P
d
= V
CC
× [I
CC(f)
+ (N × ∆I
CC
× dc)] + ∑(C
L
× V
CC
2
× f
o
)
A more accurate total power (P
T
) can be calculated if quiescent power (Pq) is also taken into consideration.
Quiescent power (P
q
) can be calculated using:
P
q
= V
CC
× [I
CCI
+ (N × ∆I
CC
× dc)]
Total power will be:
P
T
= P
d
+ P
q
The above equations provide worst-case power calculations.
Where:
N = number of inputs driven by TTL levels
∆I
CC
= increase in power supply current for each input at a TTL high level
dc = duty cycle of inputs at a TTL high level of 3.4 V
C
L
= output capacitance load
f
o
= switching frequency of an output
I
CCI
= idle current, supply current when FIFO is idle ≈ pF × f
clock
= 0.2 × f
clock
(current is due to free-running clocks)
pF = power factor (the slope of idle I
CC
versus frequency)
I
CC(f)
= active current, supply current when FIFO is transferring data