ADV7170KS View Datasheet(PDF) - Analog Devices

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ADV7170KS

Digital PAL/NTSC Video Encoder with 10-Bit SSAF™ and Advanced Power Management

Analog Devices 

APPENDIX 8

OPTIONAL DAC BUFFERING

ADV7170/ADV7171

When external buffering is needed of the ADV7170/ADV7171

DAC outputs, the configuration in Figure 83 is recommended.

This configuration shows the DAC outputs running at half

(18 mA) their full current (36 mA) capability. This will allow

the ADV7170/ADV7171 to dissipate less power; the analog cur-

rent is reduced by 50% with a RSET of 300 Ω and a RLOAD of 75 Ω.

This mode is recommended for 3.3 V operation as optimum

performance is obtained from the DAC outputs at 18 mA with a

VAA of 3.3 V. This buffer also adds extra isolation on the video

outputs (see buffer circuit in Figure 84).

When calculating absolute output full-scale current and voltage,

use the following equations:

VOUT = IOUT × RLOAD

( ) IOUT = VREF × K

RSET

K = 4.2146 constant , VREF = 1.235 V

VAA

ADV7170/ADV7171

VREF

DAC A

PIXEL

PORT

DIGITAL

CORE

300⍀

RSET

DAC B

DAC C

DAC D

OUTPUT

BUFFER

OUTPUT

BUFFER

OUTPUT

BUFFER

OUTPUT

BUFFER

CVBS

CVBS

LUMA

CHROMA

Figure 83. Output DAC Buffering Configuration

INPUT

VAA

36⍀

2N2907

75⍀

OUTPUT TO

TV/MONITOR

75⍀

Figure 84. Recommended Output DAC Buffer

REV. 0

–41–

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