CS4340 datasheet(16/28 Pages) CIRRUS

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CS4340

DS297PP3

4. APPLICATIONS

4.1

Grounding and Power Supply

Decoupling

As with any high resolution converter, the CS4340

requires careful attention to power supply and

grounding arrangements to optimize performance.

Figure 4 shows the recommended power arrange-

ment with VA connected to a clean supply. Decou-

pling capacitors should be located as close to the

device package as possible.

4.2

Oversampling Modes

The CS4340 operates in one of two oversampling

modes. Base Rate Mode supports input sample

rates up to 50 kHz while High Rate Mode supports

input sample rates up to 100 kHz. The devices op-

erate

Base

Rate

Mode

(BRM)

when

MCLK/LRCK is 256, 384 or 512 and in High Rate

Mode (HRM) when MCLK/LRCK is 128 or 192.

4.3

Recommended Power-up Sequence

RST

should be held low until the power supply,

master and left/right clocks are stable.

4.4

Popguard® Transient Control

The CS4340 uses Popguard® technology to mini-

mize the effects of output transients during power-

up and power-down. This technique, when used

with external DC-blocking capacitors in series with

the audio outputs, minimizes the audio transients

commonly produced by single-ended single-supply

converters.

When the device is initially powered-up, the audio

outputs, AOUTL and AOUTR, are clamped to

AGND. Following a delay of approximately 1000

sample periods, each output begins to ramp toward

the quiescent voltage. Approximately 10,000

left/right clock cycles later, the outputs reach VQ

and audio output begins. This gradual voltage

ramping allows time for the external DC-blocking

capacitor to charge to the quiescent voltage, mini-

mizing the power-up transient.

To prevent transients at power-down, the device

must first enter its power-down state by setting the

RST pin low. When this occurs, audio output ceas-

es and the internal output buffers are disconnected

from AOUTL and AOUTR. In their place, a soft-

start current sink is substituted which allows the

DC-blocking capacitors to slowly discharge. Once

this charge is dissipated, the power to the device

may be turned off and the system is ready for the

next power-on.

To prevent an audio transient at the next power-on,

it is necessary to ensure that the DC-blocking ca-

pacitors have fully discharged before turning off

the power or exiting the power-down state. If not, a

transient will occur when the audio outputs are ini-

tially clamped to AGND. The time that the device

must remain in the power-down state is related to

the value of the DC-blocking capacitance. For ex-

ample, with a 3.3 µF capacitor, the minimum pow-

er-down time will be approximately 0.4 seconds.

Use of the Mute Control function is recommended

for designs requiring the absolute minimum in ex-

traneous clicks and pops. Also, use of the Mute

Control function can enable the system designer to

achieve idle channel noise/signal-to-noise ratios

which are only limited by the external mute circuit.

See the CDB4340/41 data sheet for a suggested

mute circuit.

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