22

DS691A3

CS4350

4.8

Analog Output and Filtering

The Cirrus Application Note titled Design Notes for a 2-Pole Filter with Differential Input, available as AN48

at www.cirrus.com, discusses the second-order Butterworth filter and differential-to-single-ended converter

that was implemented on the CS4350 evaluation board, CDB4350. Figure 14 illustrates this

implementation. If only single-ended outputs from the CS4350 are required, the passive output filter shown

in Figure 15 can be used.

4.9

Grounding and Power Supply Arrangements

As with any high-resolution converter, the CS4350 requires careful attention to power supply and grounding

arrangements if its potential performance is to be realized. Figure 7 shows the recommended power ar-

rangements, with VA, VLC, and VLS connected to clean supplies. The use of split analog and digital ground

planes is not reccomended. However, if planes are split between digital ground and analog ground the GND

pins of the CS4350 should be connected to the analog ground plane.

All signals, especially clocks, should be kept away from the VBIAS, VFILT, and VQ pins in order to avoid

unwanted coupling into the DAC.

4.9.1

Capacitor Placement

Decoupling capacitors should be placed as close to the DAC as possible, with the low value ceramic ca-

pacitor being the closest. To further minimize impedance, these capacitors should be located on the same

layer as the DAC. If desired, all supply pins may be connected to the same supply, but a decoupling ca-

pacitor should still be placed on each supply pin.

Note:

All decoupling capacitors should be referenced to analog ground.

The CDB4350 evaluation board demonstrates the optimum layout and power supply arrangements.

AOUTx +

AOUTx -

-

+

1000 pF

C0G

562

Ω

22

µF

4.02 k

Ω

5600 pF

C0G

221

Ω

392

Ω

4.64 k

Ω

1.62 k

Ω

1.37 k

Ω

22

µF

2700 pF

C0G

.015

µF

C0G

47 k

Ω

CS4350

AGND

Analog

Output

Figure 14. Differential to Single-ended Output Filter

AOUTx +

3.3 µF

Analog

Output

2200 pF

+

10 k

Ω

CS4350

AGND

560

Ω

Figure 15. Passive Single-Ended Output Filter