Datasheet

ADV7170/ADV7171
Rev. C | Page 48 of 64
APPENDIX 7—OPTIONAL OUTPUT FILTER
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.
1.8 μ H
75R
270pF
22pF
330pF
FILTER I/P
FILTER O/P
00221-079
Figure 79. Output Filter
0
80
100k
100M
00221-080
FREQUENCY (Hz)
MAGNITUDE (dB)
1M 10M
10
20
30
40
50
60
70
Figure 80. Output Filter Plot
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
SET
of 300 Ω and a R
LOAD
of
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
AA
of 3.3 V. This buffer also adds extra isolation
on the video outputs (see the buffer circuit in Figure 82).
When calculating absolute output full-scale current and voltage,
use the following equations:
LOADOUTOUT
RIV ×=
(
)
SET
REF
OUT
R
KV
I
×
=
VVconstant,K
REF
235.12146.4 ==
ADV7170/ADV7171
V
REF
DIGITAL
CORE
PIXEL
PORT
300Ω
R
SET
V
AA
OUTPUT
BUFFER
DAC A
OUTPUT
BUFFER
OUTPUT
BUFFER
OUTPUT
BUFFER
DAC C
DAC D
DAC B
CVBS
LUMA
CHROMA
CVBS
00221-081
Figure 81. Output DAC Buffering Configuration
V
CC
+
V
CC
–
OUTPUT TO
TV MONITOR
INPUT/
OPTIONAL
FILTER O/P
5
2
3
1
4
AD8061
00221-082
Figure 82. Recommended Output DAC Buffer