ADV7177 Analog Devices, ADV7177 Datasheet - Page 37

• Manufacturer Part Number: ADV7177
• Description: Integrated Digital CCIR-601 to PAL/NTSC Video Encoder
• Manufacturer: Analog Devices

For external buffering of the ADV7177/ADV7178 DAC out-
puts, the configuration in Figure 67 is recommended. This
configuration shows the DAC outputs running at half (18 mA)
their full current (34.7 mA) capability. This will allow the
ADV7177/ADV7178 to dissipate less power, the analog current is
reduced by 50% with a R
mode is recommended for 3.3 volt operation as optimum perfor-
mance is obtained from the DAC outputs at 18 mA with a V
3.3 volts. This buffer also adds extra isolation on the video out-
REV. 0
300
PIXEL
PORT
Figure 67. Output DAC Buffering Configuration
R
SET
V
REF
DIGITAL
CORE
ADV7177/ADV7178
V
AA
SET
of 300
DAC A
DAC B
DAC C
and a R
LOAD
OUTPUT
BUFFER
OUTPUT
BUFFER
OUTPUT
BUFFER
of 75 . This
OPTIONAL DAC BUFFERING
75
75
75
AA
APPENDIX 6
of
–37–
puts, see buffer circuit in Figure 68. When calculating absolute
output full current and voltage, use the following equation:
Figure 68. Recommended Output DAC Buffer
V
I
K
OUT
INPUT
OUT
4.2146 constant , V
I
V
OUT
REF
75
R
SET
V
CC
2N2907
R
K
36
LOAD
ADV7177/ADV7178
75
REF
OUTPUT TO
TV/MONITOR
1.235 V