
This information applies to a product under development. Its characteristics and specifications are subject to change with-
out notice. Analog Devices assumes no obligation regarding future manufacturing unless otherwise agreed to in writing.
54
REV. PrA
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ADSP-2196
September 2001
The P
EXT
equation is calculated for each class of pins that
can drive as shown in
Table 24
.
A typical power consumption can now be calculated for
these conditions by adding a typical internal power dissipa-
tion with the formula in
Figure 30
.
Where:
P
EXT
is from
Table 24
P
INT
is I
DDINT
2.5V, using the calculation I
DDINT
listed in
Power Dissipation on page 52
Note that the conditions causing a worst-case P
EXT
are
different from those causing a worst-case P
INT
. Maximum
P
INT
cannot occur while 100% of the output pins are
switching from all ones to all zeros. Note also that it is not
common for an application to have 100% or even 50% of
the outputs switching simultaneously.
Test Conditions
The DSP is tested for output enable, disable, and hold time.
Output Disable Time
Output pins are considered to be disabled when they stop
driving, go into a high impedance state, and start to decay
from their output high or low voltage. The time for the
voltage on the bus to decay by – V is dependent on the
capacitive load, C
L
and the load current, I
L
. This decay time
can be approximated by the equation in
Figure 31
.
The output disable time t
DIS
is the difference between
t
MEASURED
and t
DECAY
as shown in
Figure 32
. The time
t
MEASURED
is the interval from when the reference signal
switches to when the output voltage decays –V from the
measured output high or output low voltage. The t
DECAY
is
calculated with test loads C
L
and I
L
, and with –V equal to
0.5 V.
Output Enable Time
Output pins are considered to be enabled when they have
made a transition from a high impedance state to when they
start driving. The output enable time t
ENA
is the interval
from when a reference signal reaches a high or low voltage
level to when the output has reached a specified high or low
trip point, as shown in the Output Enable/Disable diagram
(
Figure 32
). If multiple pins (such as the data bus) are
enabled, the measurement value is that of the first pin to
start driving.
Table 24. P
EXT
Calculation
Pin Type
# of Pins
% Switching
C
f
V
DD
2
= P
EXT
Address
15
50
TBD pF
25.0 MHz
10.9 V
=TBDW
MSx
1
0
TBD pF
25.0 MHz
10.9 V
=TBDW
WR
1
—
TBD pF
25 MHz
10.9 V
=TBDW
Data
16
50
TBD pF
25.0 MHz
10.9 V
=TBDW
CLKOUT
1
—
TBD pF
100 MHz
10.9 V
=TBDW
P
EXT
=TBDW
Figure 30. P
TOTAL
(Typical) Calculation
Figure 31. Decay Time Calculation
P
TOTAL
P
=
EXT
P
INT
+
t
DECAY
C
V
I
L
---------------
=
Figure 32. Output Enable/Disable
3
(
(
*(
(
:(
3
(
(
.'(
.'(
.
(
!.)(
(
3
3