CS43L22 datasheet(63/68 Pages) CIRRUS

63 / 68 page

DS792F1

CS43L22

Confidential Draft

10/7/08

10.PCB LAYOUT CONSIDERATIONS

10.1

Power Supply, Grounding

As with any high-resolution converter, the CS43L22 requires careful attention to power supply and ground-

ing arrangements if its potential performance is to be realized. Figure 1 on page 9 shows the recommended

power arrangements, with VA and VHP connected to clean supplies VD, which powers the digital circuitry,

may be run from the system logic supply. Alternatively, VD may be powered from the analog supply via a

ferrite bead. In this case, no additional devices should be powered from VD.

Extensive use of power and ground planes, ground plane fill in unused areas and surface mount decoupling

capacitors are recommended. Decoupling capacitors should be as close to the pins of the CS43L22 as pos-

sible. The low value ceramic capacitor should be closest to the pin and should be mounted on the same

side of the board as the CS43L22 to minimize inductance effects.

All signals, especially clocks, should be kept away from the FILT+ and VQ pins in order to avoid unwanted

coupling into the modulators. The VQ decoupling capacitors, particularly the 0.1 µF, must be positioned to

minimize the electrical path from AGND. The CDB43L22 evaluation board demonstrates the optimum layout

and power supply arrangements.

10.2

QFN Thermal Pad

The CS43L22 is available in a compact QFN package. The underside of the QFN package reveals a large

metal pad that serves as a thermal relief to provide for maximum heat dissipation. This pad must mate with

an equally dimensioned copper pad on the PCB and must be electrically connected to ground. A series of

vias should be used to connect this copper pad to one or more larger ground planes on other PCB layers.

In split ground systems, it is recommended that this thermal pad be connected to AGND for best perfor-

mance. The CS43L22 evaluation board demonstrates the optimum thermal pad and via configuration.

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