DF1704ESLASH2K datasheet(13/20 Pages) TI1

13 / 20 page

DF1704

SBAS099A

APPLICATIONS INFORMATION

PCB LAYOUT GUIDELINES

In order to obtain the specified performance from the DF1704

and its associated DACs, proper printed circuit board layout

is essential. Figure 11 shows two approaches for obtaining

the best audio performance.

Figure 11(a) shows a standard, mixed signal layout scheme.

The board is divided into digital and analog sections, each

with its own ground. The ground areas should be put on a

split-plane, separate from the routing and power layers. The

DF1704 and all digital circuitry should be placed over the

digital section, while the audio DACs and analog circuitry

should be located over the analog section of the board. A

common connection between the digital and analog grounds

is required and is done at a single point as shown.

For Figure 11(a), digital signals should be routed from the

DF1704 to the audio DACs using short, direct connections

to reduce the amount of radiated high-frequency energy. If

necessary, series resistors may be placed in the clock and

data signal paths to reduce or eliminate any overshoot or

undershoot present on these signals. A value of 50

Ω to 100Ω

is recommended as a starting point, but the designer should

experiment with the resistor values in order to obtain the best

results.

Figure 11(b) shows an improved method for high perfor-

mance, mixed signal board layout. This method adds digital

isolation between the DF1704 and the audio DACs, and

provides complete isolation between the digital and analog

sections of the board. Texas Instrument’s ISO150 dual

digital coupler provides excellent isolation, and operates at

speeds up to 80Mbps.

POWER SUPPLIES AND BYPASSING

The DF1704 requires a single +5V power supply for

operation. The power supply should be bypassed by a 10

µF

and 0.1

µF parallel capacitor combination. The capacitors

should be placed as close as possible to VDD (pin 22).

Aluminum electrolytics or tantalum capacitors can be used

for the 10

µF value, while ceramics may be used for the

0.1

µF value.

BASIC CIRCUIT CONNECTIONS

Figures 12 and 13 show basic circuit connections for the

DF1704. Figure 12 shows connections for Hardware mode

controls, while Figure 13 shows connections for Software

mode controls. Notice the placement of C1 and C2 in both

figures, as they are physically close to the DF1704.

TYPICAL APPLICATIONS

The DF1704 will typically be used in high-performance

audio equipment, in conjunction with high-performance

audio DACs. Figure 14 shows a typical application circuit

example, employing the DF1704, a digital audio receiver,

and two PCM1704 24-bit, 96kHz audio DACs.

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