
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
ΔV is
dependent on the capacitive load, CL, and the drive current, ID.
This ramp time can be approximated by the following equation:
The output enable time tENA is the difference between
tMEASURED_ENA and tRAMP as shown in Figure 35. The time tMEASURED_ENA is the interval from when the reference signal
switches to when the output voltage ramps
ΔV from the mea-
sured three-stated output level. tRAMP is calculated with test load
CL, drive current ID, and with
ΔV 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 37through
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
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%, VDD_IO =2.5 V)
vs. Load Capacitance at Strength 0
tRAMP
CL 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
(VDD_IO =2.5V)
R
IS
E
A
N
D
F
A
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%, VDD_IO =2.5 V)
vs. Load Capacitance at Strength 1
Figure 39. Typical Output Rise and Fall Time (10% to 90%, VDD_IO =2.5 V)
vs. Load Capacitance at Strength 2
Figure 40. Typical Output Rise and Fall Time (10% to 90%, VDD_IO =2.5 V)
vs. Load Capacitance at Strength 3
0
10
20
30
405060
70
80
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 1
(VDD_IO =2.5V)
RISE TIME
Y = 0.1501
x +0.05
FALL TIME
Y = 0.1527x + 0.7485
0
102030
40
50
60
70
80
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 2
(VDD_IO =2.5V)
RISE TIME
Y = 0.0861
x + 0.4712
FALL TIME
Y = 0.0949x + 0.8112
0
102030
40
50
60
7080
90
100
0
5
10
15
20
25
R
IS
E
A
N
D
F
A
L
T
IM
E
S
(n
s
)
LOAD CAPACITANCE (pF)
STRENGTH 3
(VDD_IO =2.5V)
RISE TIME
Y= 0.06
x +1.1362
FALL TIME
Y = 0.0691x + 1.1158