CS6403 datasheet(38/54 Pages) CIRRUS

38 / 54 page

Hardware

Power Supply

The CDB6403 requires +5V DC power to oper-

ate. Two terminal blocks provide power to the

evaluation board. One powers the analog side of

the board and the other powers the digital side.

Note that the digital power for the CS6403 itself

is derived from the analog power supply through

a 2

Ω resistor. Figure 1 shows the power supply

circuitry in greater detail.

Near-End Analog Interface

SPKROUT is a screw terminal connector which

allows you to connect directly to an 8

Ω speaker.

J14 and J15 provide the ability to access the

SPKROUT signals before they get to the connec-

tor.

These allow the system evaluator to

implement their own speaker driver in the patch

area and connect it to the SPKROUT connector.

The MICIN connector is a 1/8" stereo jack.

Only the left channel is connected since micro-

phones are usually monophonic.

Note that the

MICIN connector provides phantom power by

default. You may want to use the patch area to

provide an alternative connector.

Microphone Circuitry

A MC33078 dual op-amp performs two neces-

sary functions: provide a clean phantom power

supply, and provide additional input gain. Fig-

ure 2 shows how this circuitry is implemented.

Phantom power is provided via pin 7 of the

MC33078 through a resistor. The input voltage

for this non-inverting amplifier is VCM which is

a stable 1 V reference produced by the CS6403.

The amplifier provides a 2.3x gain to produce a

stable 2.3VDC output for phantom power.

Additional gain is provided by the other half of

the MC33078. The configuration is a differential

amplifier with the swing biased around VCM

(1VDC).

Note that the default gain of the differential am-

plifier is 6dB.

In order to change the gain,

change R105, R104, and C101. It is important

to make sure R104 and R105 are the same value,

and that R101

× C100 is approximately equal to

(R106+R104)

× C101. These conditions will en-

sure good common mode rejection.

P6KE6.8

µF

TANT C2

+5VD

DGND

P6KE6.8

µF

TANT C14

+5VA

AGND

Ω

+5VD1

DGND

+5VD

AGND

+5VA

Figure 1. Power Supply Circiutry

+5VA

VCMOUT

C103

0.1

µF

20k

Ω

R105

20k

Ω

R104

10k

Ω

R101

10k

Ω

R106

Ω

R100

Ω

R107

C100

µF

C101

0.33

µF

J12

VCM

VCMOUT

13k

Ω

R102

10k

Ω

R103

Figure 2. Microphone Phantom Power and Supplemental Amplifier

CDB6403

DS192DB3

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