CS4215 datasheet(27/52 Pages) CIRRUS

27 / 52 page

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-

p lies p ower 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

Digital

Ground

Plane

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

Analog

Ground

Plane

1/8"

CS4215

+5V

Ferrite

Bead

Ground

Connection

Figure 18. Suggested Layout Guideline

CS4215

DS76F2

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