CDB4390 datasheet(13/22 Pages) CIRRUS

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CS4390

DS264F1

Figure 13 displays the CS4390 output noise spec-

trum. The noise beyond the audio band can be fur-

ther reduced with additional analog filtering. The

applications note "Design Notes for a 2-Pole Filter

with Differential Input " discusses the second-order

Butterworth filter and differential to signal-ended

converter which was implemented on the CS4390

evaluation board, CDB4390. The CS4390 filter is a

linear phase design and does not include phase or

amplitude compensation for an external filter.

Therefore, the DAC system phase and amplitude

response will be dependent on the external analog

circuitry.

Grounding and Power Supply Decoupling

As with any high resolution converter, the CS4390

requires careful attention to power supply and

grounding arrangements to optimize performance.

Figure 1 shows the recommended power arrange-

ments with VA connected to a clean +5volt supply.

VD should be derived from VA through a 10

Ω re-

sistor. VD should not be used to power additional

digital circuitry. All mode pins which require VD

should be connected to pin 6 of the CS4390. All

mode pins which require DGND should be con-

nected to pin 5 of the CS4390. Pins 4 and 5, AGND

and DGND, should be connected together at the

CS4390. DGND for the CS4390 should not be con-

fused with the ground for the digital section of the

system. The CS4390 should be positioned over the

analog ground plane near the digital/analog ground

plane split. The analog and digital ground planes

must be connected elsewhere in the system. The

CS4390 evaluation board, CDB4390, demonstrates

this layout technique. This technique minimizes

digital noise and insures proper power supply

matching and sequencing. Decoupling capacitors

should be located as near to the CS4390 as possi-

ble.

Performance Plots

The following collection of CS4390 measurement

plots were taken from the CDB4390 evaluation

board using the Audio Precision Dual Domain Sys-

tem Two.

Figure 14 shows the frequency response at a

48 kHz sample rate. The response is flat to 20 kHz

+/-0.1 dB as specified.

Figure 15 shows THD+N versus signal amplitude

for a 1 kHz 24-bit dithered input signal. Notice that

the there is no increase in distortion as the signal

level decreases. This indicates very good low-level

linearity, one of the key benefits of delta-sigma

digital to analog conversion.

CS4390

AOUT+

AOUT-

Full Scale Input level= (AIN+) - (AIN-)= 5.66 Vpp

(2.2 + 1.4)V

2.2V

(2.2 - 1.4)V

(2.2 + 1.4)V

2.2V

(2.2 - 1.4)V

Figure 12. Full Scale Input Voltage

-20

-40

-60

-80

-100

-120

-140

-160

.25 .50

.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50

Frequency (x Fs)

Figure 13. CS4390 Output Noise Spectrum

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