Datasheet

REV. 0
ADSP-2188M
–23–
TEST CONDITIONS
Output Disable Time
Output pins are considered to be disabled when they have stopped
driving and started a transition from the measured output high
or low voltage to a high impedance state. The output disable
time (t
DIS
) is the difference of t
MEASURED
and t
DECAY
, as shown
in the Output Enable/Disable diagram. The time is the interval
from when a reference signal reaches a high or low voltage level
to when the output voltages have changed by 0.5 V from the
measured output high or low voltage.
The decay time, t
DECAY
, is dependent on the capacitive load,
C
L
, and the current load, i
L
, on the output pin. It can be
approximated by the following equation:
t
C
i
DECAY
L
L
=
× 05. V
from which
t
DIS
= t
MEASURED
– t
DECAY
is calculated. If multiple pins (such as the data bus) are disabled,
the measurement value is that of the last pin to stop driving.
1.5V
OUTPUT
INPUT
1.5V
2.0V
0.8V
Figure 18. Voltage Reference Levels for AC Measure-
ments (Except Output Enable/Disable)
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 refer-
ence signal reaches a high or low voltage level to when the output
has reached a specified high or low trip point, as shown Figure
19. If multiple pins (such as the data bus) are enabled, the mea-
surement value is that of the first pin to start driving.
2.0V
1.0V
t
ENA
REFERENCE
SIGNAL
OUTPUT
t
DECAY
V
OH
(MEASURED)
OUTPUT STOPS
DRIVING
OUTPUT
STARTS
DRIVING
t
DIS
t
MEASURED
V
OL
(MEASURED)
V
OH
(MEASURED) – 0.5V
V
OL
(MEASURED) +0.5V
HIGH-IMPEDANCE STATE. TEST CONDITIONS CAUSE
THIS VOLTAGE LEVEL TO BE APPROXIMATELY 1.5V.
V
OH
(MEASURED)
V
OL
(MEASURED)
Figure 19. Output Enable/Disable
TO
OUTPUT
PIN
50pF
1.5V
I
OH
I
OL
Figure 20. Equivalent Loading for AC Measurements
(Including All Fixtures)