CS53L21 datasheet(59/66 Pages) CIRRUS

59 / 66 page

DS700PP1

CS53L21

9. PCB LAYOUT CONSIDERATIONS

9.1

Power Supply, Grounding

As with any high-resolution converter, the CS53L21 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 connected to a clean supply. 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 CS53L21 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 CS53L21 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 CS53L21 evaluation board demonstrates the optimum layout and power supply

arrangements.

9.2

QFN Thermal Pad

The CS53L21 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 CS53L21 evaluation board demonstrates the optimum thermal pad and via configuration.

CS53L21 データシート(PDF) 59 Page - Cirrus Logic