Datasheet

DF1704
13
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 50Ω 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 10µF
and 0.1µF parallel capacitor combination. The capacitors
should be placed as close as possible to V
DD
(pin 22).
Aluminum electrolytics or tantalum capacitors can be used
for the 10µF value, while ceramics may be used for the
0.1µF 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 C
1
and C
2
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.