ADV7342 datasheet(65/88 Pages) AD

65 / 88 page

ADV7342/ADV7343

Rev. 0 | Page 65 of 88

PRINTED CIRCUIT BOARD LAYOUT AND DESIGN

DAC CONFIGURATIONS

The ADV7342/ADV7343 contain 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 ADV7342/ADV7343 contain 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 ADV7342/ADV7343 contain 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 ADV7342/ADV7343 contain an on-chip voltage reference

that can be used as a board-level voltage reference via the VREF

pin. Alternatively, the ADV7342/ADV7343 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 ADV7342/

ADV7343. 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 ADV7342/ADV7343 DAC outputs if

the ADV7342/ADV7343 are 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. ADV7342/ADV7343 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

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