adv7171a-dbrd Analog Devices, Inc., adv7171a-dbrd Datasheet - Page 48

• Manufacturer Part Number: adv7171a-dbrd
• Description: Digital Pal/ntsc Video Encoder With 10-bit Ssaf ?nd Advanced Power Management
• Manufacturer: Analog Devices, Inc.

ADV7170/ADV7171
APPEN
If an output filter is required for the CVBS, Y, UV, Chroma, and
RGB outputs of the ADV7170/ADV7171, the filter shown in
Figure 79 can be used. Plots of the filter characteristics are
shown in Figure 80. An output filter is not required if the
outputs of the ADV7170/ADV7171 are connected to most
analog monitors or analog TVs. However, if the output signals
are applied to a system where sampling is used (for example,
digital TVs), then a filter is required to prevent aliasing.
FILTER I/P
10
20
30
40
50
60
70
80
100k
0
DIX 7—OPTIONAL OUTPUT FILTER
75R
Figure 80. Output Filter Plot
Figure 79. Output Filter
1M
270pF
FREQUENCY (Hz)
1.8 µ H
22pF
330pF
10M
FILTER O/P
100M
Rev. B | Page 48 of 64
APPENDIX 8—OPTIONAL DAC BUFFERING
When external buffering of the ADV7170/ADV7171 DAC
outputs is needed, the configuration in Figure 81 is recom-
mended. This configuration shows the DAC outputs running
at half (18 mA) their full current (36 mA) capability. This allows
the ADV7170/ADV7171 to dissipate less power; the analog
current is reduced by 50% with a R
75 Ω. This mode is recommended for 3.3 V operation, because
optimum performance is obtained from the DAC outputs at
18 mA with a V
on the video outputs (see the buffer circuit in Figure 82).
When calculating absolute output full-scale current and voltage,
use the following equations:
300Ω
PIXEL
PORT
FILTER O/P
V
I
K
OPTIONAL
OUT
OUT
=
INPUT/
R
. 4
SET
=
=
V
2146
DIGITAL
REF
Figure 81. Output DAC Buffering Configuration
(
I
CORE
V
Figure 82. Recommended Output DAC Buffer
OUT
ADV7170/ADV7171
REF
AA
R
V
AA
constant,
SET
×
of 3.3 V. This buffer also adds extra isolation
×
4
3
R
K
AD8061
LOAD
)
V
V
CC
CC
5
2
V
+
–
DAC B
DAC C
DAC D
DAC A
REF
=
1
. 1
SET
235
of 300 Ω and a R
V
OUTPUT
OUTPUT
BUFFER
OUTPUT
BUFFER
OUTPUT
BUFFER
BUFFER
OUTPUT TO
TV MONITOR
LOAD
of
CVBS
CV
LUMA
CHROMA
BS