Cirrus Logic CS43L21 - Manual (Page 60)

60 DS723F1
CS43L21
9. PCB LAYOUT CONSIDERATIONS
9.1 Power Supply, Grounding
As with any high-resolution converter, the CS43L21 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 VA_HP connected to clean supplies. VD, which powers the digital circuit-
ry, 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 CS43L21 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 CS43L21 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 FILT+
and VQ decoupling capacitors, particularly the 0.1 µF, must be positioned to minimize the electrical path
from FILT+ and AGND. The CS43L21 evaluation board demonstrates the optimum layout and power supply
arrangements.
9.2 QFN Thermal Pad
The CS43L21 is available in a compact QFN package. The under side 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 CS43L21 evaluation board demonstrates the optimum thermal pad and via configuration.