Datasheet

REV. C
ADSP-21065L
–36–
OUTPUT DRIVE CURRENT
SOURCE VOLTAGE – V
80
0
3.50
SOURCE CURRENT – mA
0.50 1.00 1.50 2.00 2.50 3.00
60
–40
–100
–120
20
–20
40
0
–80
–60
3.3V, +25 ⴗ C
3.6V, –40 ⴗ C
3.1V, +100 ⴗ C
3.6V, –40 ⴗ C
V
OL
V
OH
3.1V, +85 ⴗ C
3.1V, +100 ⴗ C
3.1V, +85 ⴗ C
3.3V, +25 ⴗ C
Figure 24. Typical Drive Currents
TEST CONDITIONS
Output Disable Time
Output pins are considered to be disabled when they stop driv-
ing, 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 DV is dependent on the capacitive load, C
L
and
the load current, I
L
. This decay time can be approximated by
the following equation:
t
CV
I
DECAY
L
L
=
¥D
The output disable time t
DIS
is the difference between t
MEASURED
and t
DECAY
as shown in Figure 26. The time t
MEASURED
is the
interval from when the reference signal switches to when the
output voltage decays DV from the measured output high or
output low voltage. t
DECAY
is calculated with test loads C
L
and
I
L
, and with DV 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. If multiple pins (such as
the data bus) are enabled, the measurement value is that of the
first pin to start driving.
Example System Hold Time Calculation
To determine the data output hold time in a particular system,
first calculate t
DECAY
using the equation given above. Choose DV
to be the difference between the ADSP-21065L’s output voltage
and the input threshold for the device requiring the hold time. A
typical DV will be 0.4 V. C
L
is the total bus capacitance (per
data line), and I
L
is the total leakage or three-state current (per
data line). The hold time will be t
DECAY
plus the minimum
disable time (i.e., t
DATRWH
for the write cycle).
REFERENCE
SIGNAL
t
DIS
OUTPUT STARTS
DRIVING
V
OH (MEASURED)
– ⌬V
V
OL (MEASURED)
+ ⌬V
t
MEASURED
V
OH (MEASURED)
V
OL (MEASURED)
2.0V
1.0V
V
OH (MEASURED)
V
OL (MEASURED)
HIGH-IMPEDANCE STATE.
TEST CONDITIONS CAUSE
THIS VOLTAGE TO BE
APPROXIMATELY 1.5V
OUTPUT STOPS
DRIVING
t
ENA
t
DECAY
OUTPUT
Figure 25. Output Enable
+1.5V
50pF
TO
OUTPUT
PIN
I
OL
I
OH
Figure 26. Equivalent Device Loading for AC Measure-
ments (Includes All Fixtures)
INPUT OR
OUTPUT
1.5V
1.5V
Figure 27. Voltage Reference Levels for AC Measure-
ments (Except Output Enable/Disable)