ad1848 Analog Devices, Inc., ad1848 Datasheet - Page 26

• Manufacturer Part Number: ad1848
• Description: Parallel-port 16-bit Soundport Stereo Codec
• Manufacturer: Analog Devices, Inc.

AD1848K
Figure 21 illustrates reference bypassing. V
connected to its bypass capacitors.
Figure 22 illustrates signal-path filtering capacitors, L_FILT
and R_FILT. Note that AD1848Ks will perform satisfactorily
with 0.1 F capacitors; increasing the value to 1.0 F does im-
prove performance at very low frequencies, however.
The crystals shown in the crystal connection circuitry of Figure
23 should be fundamental-mode and parallel-tuned. Two
sources for the exact crystals specified are Component Market-
ing Services in Massachusetts, U.S. at 617-762-4339 and Cardi-
nal Components in New Jersey, U.S. at 201-746-0333. Note
that using the exact data sheet frequencies is not required and
that external clock sources can be used to overdrive the
AD1848K’s internal oscillators. (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 jit-
ter external input clocks.
Analog Devices also recommends a pull-down resistor for
PWRDWN.
Good, standard engineering practices should be applied for
power supply decoupling. Decoupling capacitors should be
placed as close as possible to package pins. If a separate analog
Figure 22. AD1848K External Filter Capacitor Connections
20–64pF
V
Figure 21. AD1848K Voltage Reference Bypassing
REF
XTAL1I
_
F
Figure 23. AD1848K Crystal Connections
24.576MHz
10µF
XTAL1O
1.0 F
L_FILT
20–64pF
0.1µF
20–64pF
V
R_FILT
REF
1.0 F
XTAL2I
REF
16.9344MHz
_F should only be
10µF
XTAL2O
20–64pF
–26–
power supply is not available, we recommend the circuit shown
in Figure 24 for using a single +5 V supply. Ferrite beads suffice
for the inductors shown. 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 AD1848K. 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 AD1848K. Other schemes may
also yield satisfactory results. If the split ground plane recom-
mended here is not possible, the AD1848K should be entirely
over the analog ground plane with the 74_245 transceiver over
the digital plane.
+5V SUPPLY
Figure 25. AD1848K Recommended Ground Plane
DIGITAL GROUND PLANE
Figure 24. AD1848K Recommended Power Supply
Bypassing
V
DD
0.1 F
FERRITE
0.1 F
FERRITE
AD1848K
0.1 F
GNDD
V
GNDD
DD
1 F
1 F
V
DD
1.6
R_FILT
R_AUX2
0.1 F
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. 0
0.1 F
V
CC