
ADSP-21266
Rev. B
|
Page 37 of 44
|
May 2005
OUTPUT DRIVE CURRENTS
Figure 28
shows typical I-V characteristics for the output driv-
ers of the ADSP-21266. The curves represent the current drive
capability of the output drivers as a function of output voltage.
TEST CONDITIONS
The ac signal specifications (timing parameters) appear in
Table 11 on Page 19
through
Table 32 on Page 36
. These include
output disable time, output enable time, and capacitive loading.
Timing is measured on signals when they cross the 1.5 V level as
described in
Figure 30
. All delays (in nanoseconds) are mea-
sured between the point that the first signal reaches 1.5 V and
the point that the second signal reaches 1.5 V.
CAPACITIVE LOADING
Output delays and holds are based on standard capacitive loads:
30 pF on all pins (see
Figure 29
).
Figure 32
shows graphically
how output delays and holds vary with load capacitance (note
that this graph or derating does not apply to output disable
delays). The graphs of
Figure 31
,
Figure 32
, and
Figure 33
may
not be linear outside the ranges shown for Typical Output Delay
vs. Load Capacitance and Typical Output Rise Time (20%
–
80%,
V=Min) vs. Load Capacitance.
Figure 28. Typical Drive
Figure 29. Equivalent Device Loading for AC Measurements
(Includes All Fixtures)
Figure 30. Voltage Reference Levels for AC Measurements
SWEEP(VDDEXT) VOLTAGE (V)
–20
0
3.5
0.5
1
1.5
2
2.5
3
0
–40
–30
20
40
–10
S
VOL
3.11V, 125°C
3.3V, 25°C
3.47V, –45°C
VOH
30
10
3.11V, 125°C
3.3V, 25°C
3.47V, –45°C
1.5V
30pF
TO
OUTPUT
PIN
50
INPUT
OR
OUTPUT
1.5V
1.5V
Figure 31. Typical Output Rise Time
(20%
–
80%, V
DDEXT
= Max)
Figure 32. Typical Output Rise/Fall Time
(20%
–
80%, V
DDEXT
= Min)
LOAD CAPACITANCE (pF)
8
0
0
100
250
12
4
2
10
6
R
200
150
50
FALL
y = 0.0467x + 1.6323
y = 0.045x + 1.524
RISE
LOAD CAPACITANCE (pF)
12
0
50
100
150
200
250
10
8
6
4
R
2
0
RISE
FALL
y = 0.049x + 1.5105
y = 0.0482x + 1.4604