ADV7344 datasheet(65/88 Pages) AD

65 / 88 page

ADV7344

Rev. 0 | Page 65 of 88

PRINTED CIRCUIT BOARD LAYOUT AND DESIGN

DAC CONFIGURATIONS

The ADV7344 contains six DACs. All six 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, RL.

DAC 1, DAC 2, and DAC 3 can also 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, RL. Full-drive is the recommended

mode of operation for DAC 1, DAC 2, and DAC 3.

The ADV7344 contains two RSET pins. A resistor connected

between the RSET1 pin and AGND is used to control the full-

scale output current and, therefore, the DAC output voltage

levels of DAC 1, DAC 2, and DAC 3. For low drive operation,

RSET1 must have a value of 4.12 kΩ, and RL must have a value of

300 Ω. For full-drive operation, RSET1 must have a value of 510 Ω,

and RL must have a value of 37.5 Ω.

A resistor connected between the RSET2 pin and AGND is used

to control the full-scale output current and, therefore, the DAC

output voltage levels of DAC 4, DAC 5, and DAC 6. RSET2 must

have a value of 4.12 kΩ, and RL must have a value of 300 Ω (that

is, low drive operation only).

The resistors connected to the RSET1 and RSET2 pins should have a

1% tolerance.

The ADV7344 contains two compensation pins, COMP1 and

COMP2. A 2.2 nF compensation capacitor should be connected

from each of these pins to VAA.

VOLTAGE REFERENCE

The ADV7344 contains an on-chip voltage reference that can be

used as a board-level voltage reference via the VREF pin.

Alternatively, the ADV7344 can be used with an external

voltage reference by connecting the reference source to the VREF

pin. For optimal performance, an external voltage reference

such as the AD1580 should be used with the ADV7344. If an

external voltage reference is not used, a 0.1 μF capacitor should

be connected from the VREF pin to VAA.

VIDEO OUTPUT BUFFER AND OPTIONAL

OUTPUT FILTER

An output buffer is necessary on any DAC that operates in low

drive mode (RSET = 4.12 kΩ, RL = 300 Ω). Analog Devices, Inc.

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 ADV7344 DAC outputs if the ADV7344

is connected to a device that requires this filtering. 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, ADA4411-3, and ADA4410-6 integrated

video filter buffers should be considered.

Table 53. ADV7344 Output Rates

Input Mode

(0x01, Bits[6:4])

PLL Control

(0x00, Bit 1)

Output Rate

(MHz)

Off

(2x)

SD Only

216

(16x)

Off

(1x)

ED Only

216

(8x)

Off

74.25

(1x)

HD Only

297

(4x)

Table 54. Output Filter Requirements

Application

Oversampling

Cutoff

Frequency

(MHz)

Attenuation

–50 dB @ (MHz)

2×

>6.5

20.5

16×

>6.5

209.5

1×

>12.5

14.5

8×

>12.5

203.5

1×

>30

44.25

4×

>30

267

560Ω

600Ω

22pF

600Ω

DAC

OUTPUT

75Ω

BNC

OUTPUT

10µH

560Ω

Figure 84. Example of Output Filter for SD, 16× Oversampling

560Ω

6.8pF

600Ω

6.8pF

600Ω

DAC

OUTPUT

75Ω

BNC

OUTPUT

4.7µH

560Ω

Figure 85. Example of Output Filter for ED, 8× Oversampling

DAC

OUTPUT

390nH

33pF

75Ω

500Ω

300Ω

75Ω

BNC

OUTPUT

500Ω

Figure 86. Example of Output Filter for HD, 4× Oversampling

ADV7344 Datasheet(PDF) 65 Page - Analog Devices

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