AD1846 Analog Devices, AD1846 Datasheet - Page 26

• Manufacturer Part Number: AD1846
• Description: Low Cost Parallel-port 16-bit Soundport Stereo Codec
• Manufacturer: Analog Devices

AD1846
Figure 21 illustrates reference bypassing. V
connected to its bypass capacitors.
Figure 22 illustrates signal-path filtering capacitors, L_FILT
and R_FILT. The 1.0 F capacitors required by the AD1846
can be of any type. Note that AD1846s will perform satisfacto-
rily with 0.1 F capacitors; however, low frequency performance
will be degraded.
The crystals shown in the crystal connection circuitry of Figure
23 should be fundamental-mode and parallel-tuned. Note that
using the exact data sheet frequencies is not required and that
external clock sources can be used to drive the crystal inputs.
(See the description of the CFS2:0 control bits above.) If using
an external clock source, apply it to the crystal input pins while
leaving the crystal output pins unconnected. Attention should
be paid to providing low jitter external input clocks.
Low cost ceramic resonators may be substituted for the crystals
to supply the time base to the AD1846.
Analog Devices recommends a pull-down resistor for
PWRDWN.
20–64pF
V
REF
Figure 22. External Filter Capacitor Connections
XTAL1I
_
F
Figure 21. Voltage Reference Bypassing
24.576MHz
10 F
Figure 23. Crystal Connections
XTAL1O
1.0 F
L_FILT
20–64pF
0.1 F
20–64pF
V
REF
R_FILT
XTAL2I
1.0 F
REF
16.9344MHz
_F should only be
XTAL2O
10 F
20–64pF
–26–
Good, standard engineering practices should be applied for
power supply decoupling. Decoupling capacitors should be
place as close as possible to package pins. If a separate analog
power supply is not available, we recommend the circuit shown
in Figure 24 for using a single +5 V supply. This circuitry
should be as close to the supply pins as is practical.
Analog Devices recommends a split ground plane as shown in
Figure 25. The analog plane and the digital plane are connected
directly under the AD1846. Splitting the ground plane directly
under the SoundPort Codec is optimal because analog pins will
be located above the analog ground plane and digital pins will
be located directly above the digital ground plane for the best
isolation. The digital ground and analog grounds should be tied
together in the vicinity of the AD1846. Other schemes may also
yield satisfactory results. If the split ground plane recommended
here is not possible, the AD1846 should be entirely over the
analog ground plane with the 74_245 transceiver over the digital
plane.
+5V SUPPLY
Figure 24. Recommended Power Supply Bypassing
DIGITAL GROUND PLANE
Figure 25. Recommended Ground Plane
FERRITE/INDUCTOR
FERRITE/INDUCTOR
V
DD
0.1 F
0.1 F
AD1846
0.1 F
V
GNDD
GNDD
DD
1 F
1 F
V
DD
1.6
0.1 F
R_AUX2
R_FILT
ANALOG GROUND PLANE
V
0.1 F
DD
V
1 F
DD
0.1 F
V
0.1 F
DD
0.1 F
V
DD
V
CC
0.1 F
REV. A
0.1 F
V
CC