ADSP-2184 Analog Devices, ADSP-2184 Datasheet - Page 27

• Manufacturer Part Number: ADSP-2184
• Description: DSP Microcomputer
• Manufacturer: Analog Devices

CAPACITIVE LOADING
Figures 22 and 23 show the capacitive loading characteristics of
the ADSP-2184.
Figure 22. Typical Output Rise Time vs. Load Capacitance,
C
Figure 23. Typical Output Valid Delay or Hold vs. Load
Capacitance, C
Temperature)
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 out-
put disable time (t
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
load, i
lowing equation:
from which
REV. 0
DECAY
L
(at Maximum Ambient Operating Temperature)
NOMINAL
L
, is dependent on the capacitive load, C
, on the output pin. It can be approximated by the fol-
30
25
20
15
10
5
0
0
18
16
14
12
10
–2
–4
–6
8
6
4
2
T = +85 C
V
0
DD
L
= 4.5V
50
(at Maximum Ambient Operating
DIS
t
DIS
) is the difference of t
50
t
DECAY
= t
100
MEASURED
100
C
L
150
C
– pF
C
L
L
– pF
i
– t
L
0.5V
150
DECAY
200
MEASURED
L
250
, and the current
200
and t
300
250
DECAY
,
–27–
is calculated. If multiple pins (such as the data bus) are dis-
abled, the measurement value is that of the last pin to stop
driving.
Figure 24. Voltage Reference Levels for AC Measure-
ments (Except Output Enable/Disable)
Output Enable Time
Output pins are considered to be enabled when that have made
a transition from a high-impedance state to when they start
driving. The output enable time (t
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.
Figure 26. Equivalent Device Loading for AC Measure-
ments (Including All Fixtures)
REFERENCE
OUTPUT
(MEASURED)
(MEASURED)
SIGNAL
OUTPUT
INPUT
OR
V
V
OUTPUT
OL
OH
OUTPUT STOPS
Figure 25. Output Enable/Disable
PIN
t
TO
t
MEASURED
DIS
DRIVING
1.5V
50pF
HIGH-IMPEDANCE STATE. TEST CONDITIONS CAUSE
THIS VOLTAGE LEVEL TO BE APPROXIMATELY 1.5V.
V
V
OH
OL
t
DECAY
(MEASURED) +0.5V
(MEASURED) – 0.5V
ENA
I
I
OL
OH
) is the interval from when
ADSP-2184
1.0V
2.0V
OUTPUT
DRIVING
STARTS
t
ENA
+1.5V
1.5V
V
(MEASURED)
V
(MEASURED)
OH
OL