Datasheet

Data Sheet ADV7390/ADV7391/ADV7392/ADV7393
Rev. G | Page 69 of 108
PRINTED CIRCUIT BOARD LAYOUT AND DESIGN
UNUSED PINS
If the
HSYNC
and
VSYNC
pins are not used, they should be tied
to V
DD_IO
through a pull-up resistor (10 kΩ or 4.7 kΩ). Any
other unused digital inputs should be tied to ground. Unused
digital output pins should be left floating. DAC outputs can
either be left floating or connected to GND. Disabling these
outputs is recommended.
DAC CONFIGURATIONS
The ADV739x contains three DACs. All three DACs can be
configured to operate in full-drive mode. Full-drive mode is
defined as 34.7 mA full-scale current into a 37.5 Ω load, R
L
.
Full drive is the recommended mode of operation for the DACs.
Alternatively, all three DACs can be configured to operate in low-
drive mode. Low-drive mode is defined as 4.33 mA full-scale
current into a 300 Ω load, R
L
.
The ADV739x contains an R
SET
pin. A resistor connected between
the R
SET
pin and AGND is used to control the full-scale output
current and, therefore, the output voltage levels of DAC 1, DAC 2,
and DAC 3. For full-drive operation, R
SET
must have a value of
510 Ω and RL must have a value of 37.5 Ω. For low-drive opera-
tion, R
SET
must have a value of 4.12 kΩ, and R
L
must have a value
of 300 Ω. The resistor connected to the R
SET
pin should have a
1% tolerance.
The ADV739x contains a compensation pin, COMP. A 2.2 nF
compensation capacitor should be connected from the COMP
pin to V
AA
.
VIDEO OUTPUT BUFFER AND OPTIONAL
OUTPUT FILTER
An output buffer is necessary on any DAC that operates in low-
drive mode (R
SET
= 4.12 kΩ, R
L
= 300 Ω). Analog Devices
produces a range of op amps suitable for this application, for
example, the AD8061. For more information about line driver
buffering circuits, see the relevant op amp data sheet.
An optional reconstruction (anti-imaging) low-pass filter (LPF)
may be required on the ADV739x DAC outputs. The filter
specifications vary with the application. The use of 16× (SD),
8× (ED), or 4× (HD) oversampling can remove the requirement
for a reconstruction filter altogether.
For applications requiring an output buffer and reconstruction
filter, the ADA4430-1 and ADA4411-3 integrated video filter
buffers should be considered.
Table 57. ADV739x Output Rates
Input Mode
(Subaddress 0x01,
Bits[6:4]) Oversampling Output Rate (MHz)
SD Off 27 (2×)
On 108 (8×)
On 216 (16×)
ED Off 27 (1×)
On 108 (4×)
On 216 (8×)
HD Off 74.25 (1×)
On 148.5 (2×)
On 297 (4×)
Table 58. Output Filter Requirements
Application Oversampling
Cutoff
Frequency
(MHz)
Attenuation
–50 dB
at
(MHz)
SD 2× > 6.5 20.5
8× > 6.5 101.5
16×
> 6.5
209.5
ED 1× > 12.5 14.5
4× > 12.5 95.5
8× > 12.5 203.5
HD 1× > 30 44.25
2× > 30 118.5
4×
> 30
267
Figure 87. Example of Output Filter for SD, 16× Oversampling
Figure 88. Example of Output Filter for ED, 8× Oversampling
Figure 89. Example of Output Filter for HD, 4× Oversampling
560Ω
600Ω22pF600Ω
DAC
OUTPUT
75Ω
BNC
OUTPUT
10µH
560Ω
3
4
1
06234-086
560Ω
6.8pF
600Ω
6.8pF
600Ω
DAC
OUTPUT
75Ω
BNC
OUTPUT
4.7µH
560Ω
3
4
1
06234-087
DAC
OUTPUT
390nH
33pF
33pF
75Ω
500Ω
300Ω
75Ω
BNC
OUTPUT
500Ω
3
4
1
3
4
1
06234-088