ADSP-21065 Analog Devices, ADSP-21065 Datasheet - Page 36

• Manufacturer Part Number: ADSP-21065
• Description: DSP Microcomputer
• Manufacturer: Analog Devices

ADSP-21065L
OUTPUT DRIVE CURRENT
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 ∆V is dependent on the capacitive load, C
the load current, I
the following equation:
The output disable time t
and t
interval from when the reference signal switches to when the
output voltage decays ∆V from the measured output high or
output low voltage. t
I
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
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.
L
, and with ∆V equal to 0.5 V.
DECAY
–100
–120
–20
–40
–60
–80
20
80
60
40
0
as shown in Figure 26. The time t
0
3.1V, +100 C
3.1V, +85 C
0.50
3.3V, +25 C
3.6V, –40 C
L
. This decay time can be approximated by
DECAY
t
DECAY
1.00
DIS
V
SOURCE VOLTAGE – V
OL
3.1V, +100 C
is calculated with test loads C
is the difference between t
1.50
=
C
ENA
L
3.3V, +25 C
2.00
I
× ∆
L
is the interval from when a
V
OH
V
2.50
3.1V, +85 C
3.6V, –40 C
MEASURED
3.00
3.50
MEASURED
is the
L
L
and
and
Example System Hold Time Calculation
To determine the data output hold time in a particular system,
first calculate t
to be the difference between the ADSP-21065L’s output voltage
and the input threshold for the device requiring the hold time. A
typical ∆V will be 0.4 V. C
data line), and I
data line). The hold time will be t
disable time (i.e., t
REFERENCE
V
V
OH (MEASURED)
OL (MEASURED)
OUTPUT
SIGNAL
INPUT OR
OUTPUT
t
OUTPUT
DIS
DECAY
OUTPUT STOPS
L
PIN
DRIVING
TO
is the total leakage or three-state current (per
DATRWH
1.5V
using the equation given above. Choose ∆V
50pF
t
MEASURED
V
V
OH (MEASURED)
OL (MEASURED)
t
DECAY
L
for the write cycle).
is the total bus capacitance (per
HIGH-IMPEDANCE STATE.
TEST CONDITIONS CAUSE
THIS VOLTAGE TO BE
APPROXIMATELY 1.5V
DECAY
+ V
I
– V
I
OH
OL
plus the minimum
OUTPUT STARTS
t
ENA
1.0V
2.0V
DRIVING
1.5V
+1.5V
V
V
OH (MEASURED)
OL (MEASURED)