Rev. C
|
Page 38 of 48
|
December 2006
ADSP-TS201S
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 driv-
ing. The time for the voltage on the bus to ramp by
Δ
V is
dependent on the capacitive load, C
L
, and the drive current, I
D
.
This ramp time can be approximated by the following equation:
The output enable time t
ENA
is the difference between
t
MEASURED_ENA
and t
RAMP
as shown in
Figure 35
. The time
t
MEASURED_ENA
is the interval from when the reference signal
switches to when the output voltage ramps
Δ
V from the mea-
sured three-stated output level. t
RAMP
is calculated with test load
C
L
, drive current I
D
, and with
Δ
V equal to 0.4 V.
Capacitive Loading
Output valid and hold are based on standard capacitive loads:
30 pF on all pins (see
Figure 36
). The delay and hold specifica-
tions given should be derated by a drive strength related factor
for loads other than the nominal value of 30 pF.
Figure 37
through
Figure 44
show how output rise time varies with capac-
itance.
Figure 45
graphically shows how output valid varies with
load capacitance. (Note that this graph or derating does not
apply to output disable delays; see
Output Disable Time on
Page 37
.) The graphs of
Figure 37
through
Figure 45
may not be
linear outside the ranges shown.
Figure 36. Equivalent Device Loading for AC Measurements
(Includes All Fixtures)
Figure 37. Typical Output Rise and Fall Time (10% to 90%, V
DD_IO
= 2.5 V)
vs. Load Capacitance at Strength 0
t
RAMP
C
L
V
Δ
(
)
I
D
⁄
=
1.25V
TO
OUTPUT
PIN
30pF
50
⍀
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
RISE TIME
Y = 0.259x + 3.0842
STRENGTH 0
(V
DD_IO
= 2.5V)
R
IS
E
A
N
D
F
A
L
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
FALL TIME
Y = 0.251x + 4.2245
Figure 38. Typical Output Rise and Fall Time (10% to 90%, V
DD_IO
= 2.5 V)
vs. Load Capacitance at Strength 1
Figure 39. Typical Output Rise and Fall Time (10% to 90%, V
DD_IO
= 2.5 V)
vs. Load Capacitance at Strength 2
Figure 40. Typical Output Rise and Fall Time (10% to 90%, V
DD_IO
= 2.5 V)
vs. Load Capacitance at Strength 3
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 1
(V
DD_IO
= 2.5V)
RISE TIME
Y = 0.1501
x + 0.05
FALL TIME
Y = 0.1527x + 0.7485
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 2
(V
DD_IO
= 2.5V)
RISE TIME
Y = 0.0861
x + 0.4712
FALL TIME
Y = 0.0949x + 0.8112
0
10
20
30
40
50
60
70
80
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 3
(V
DD_IO
= 2.5V)
RISE TIME
Y = 0.06
x + 1.1362
FALL TIME
Y = 0.0691x + 1.1158
Содержание TigerSHARC ADSP-TS201S
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