CS4215 Datasheet, PDF (27/52 Pages) Cirrus Logic – 16-Bit Multimedia Audio Codec

Digital
Ground
Plane
> 1/8"
Ground
Connection
+5V
Ferrite
Bead
CS4215
Analog
Ground
Plane
CS4215
Note that the CS4215
is oriented with its
digital pins towards the
digital end of the board.
CPU & Digital
Logic
Codec
digital
signals
Codec
analog
signals &
Components
Figure 18. Suggested Layout Guideline
POWER SUPPLY AND GROUNDING
When using separate supplies, the digital power
should be connected to the CS4215 via a ferrite
bead, positioned closer than 1" to the device (see
Figure 1). The codec VA1, VA2 pins should be
derived from the cleanest power source available.
If only one supply is available, use the suggested
arrangement in Figure 17. VA1 supplies analog
power to the ADCs and DACs while VA2 sup-
plies power to the output power drivers
(headphones and speaker). The large currents
necessary for VA2 are not flowing through the
2.0 Ω resistor, and therefore do not corrupt the
VA1 converter supply.
The CS4215 along with associated analog cir-
cuitry, should be positioned near to the edge of
the circuit board, and have its own, separate,
ground plane. On the CS4215, the analog and
digital grounds are internally connected; there-
fore, the four ground pins must be externally
connected with zero impedance between ground
pins. The best solution is to place the entire chip
on a solid ground plane as shown in Figure 18.
Preferably, it should also have its own power
plane. A single connection between the CS4215
ground and the board ground should be posi-
tioned as shown in Figure 18.
Figure 19 illustrates the optimum ground and de-
coupling layout for the CS4215 assuming a
surface-mount socket and leaded decoupling ca-
pacitors. Surface-mount sockets are useful since
the pad locations are exactly the same as the ac-
tual chip; therefore, given that space for the
socket is left on the board, the socket can be op-
tional for production. Figure 19 depicts the top
layer containing signal traces and assumes the
bottom or inter-layer contains a solid analog
ground plane. The important points with regards
to this diagram are that the ground plane is
SOLID under the codec and connects all codec
ground pins with thick traces providing the abso-
lute lowest impedance between ground pins. The
decoupling capacitors are placed as close as pos-
sible to the device which, in this case, is the
socket boundary. The lowest value capacitor is
DS76F2
27