CS4294SLASHCS4298 datasheet(51/66 Pages) CIRRUS

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CS4202

DS549PP2

Mic Volume Register (Index 0Eh) the pre-amplifier

gain can be set to 0 dB, 10 dB, 20 dB, or 30 dB.

10.1.4

PC Beep Input

The PC_BEEP input is useful for mixing the output

of the “beeper” (timer chip), provided in most PCs,

with the other audio signals. When the CS4202 is

held in reset, PC_BEEP is passed directly to the line

output. This allows the system sounds or “beeps” to

be available before the AC ’97 interface has been ac-

tivated. Figure 21 illustrates a typical input circuit for

the PC_BEEP input. If PC_BEEP is driven from a

CMOS gate, the 4.7 k

Ω resistor should be tied to an-

alog ground instead of +5VA. Although this input is

described for a low-quality “beeper”, it is of the same

high-quality as all other analog inputs and may be

used for other purposes.

10.1.5

Phone Input

One application of the PHONE input is to interface

to the output of a modem analog front end (AFE) de-

vice so that modem dialing signals and protocol ne-

gotiations may be monitored through the audio

system. Figure 22 shows a design for a modem con-

nection where the output is fed from the CS4202

MONO_OUT pin through a divider. The divider ra-

tio shown does not attenuate the signal, providing an

output voltage of 1 VRMS. If a lower output voltage

is desired, the resistors can be replaced with appro-

priate values, as long as the total load on the output

is kept greater than 10 k

Ω. The PHONE input is di-

vided by 6 dB to accommodate a line-level source of

2 VRMS.

10.2

Analog Outputs

The analog output section provides a stereo, a head-

phone, and a mono output. The MONO_OUT,

LINE_OUT_L, and LINE_OUT_R pins require

680 pF to 1000 pF NPO dielectric capacitors be-

tween the corresponding pin and analog ground.

Each analog output is DC-biased up to the Vrefout

voltage signal reference, nominally 2.4 V. This re-

quires the outputs be AC-coupled to external circuit-

ry (AC loads must be greater than 10 k

Ω for the line

output or 32

Ω for the headphone output). The head-

phone coupling capacitors should be 220

µF or great-

er to minimize low frequency roll-off.

10.2.1

Stereo Outputs

The LINE_OUT and HP_OUT stereo outputs de-

pend on the configuration of the HPCFG pin. As

shown in Figure 23, if the HPCFG pin is left floating,

0.1

µ F

X7R

100

Ω

0.1

µ F

X7R

MIC1/MIC2

µF

ELEC

AGND

+5VA

2.2 k

Ω

1.5 k

Ω

AGND

Figure 20. Microphone Input

4.7 k

Ω

PC_BEEP

+5VA (Low Noise) or

AGND if CMOS Source

PC-BEEP-BUS

47 k

Ω

2.7 nF

X7R

0.1

µF

X7R

AGND

Figure 21. PC_BEEP Input

PHONE

MONO_OUT

PHONE

MONO_OUT

6.8 k

Ω

1.0

µF

0 Ω

6.8 k

Ω

1.0

µF

47 k

Ω

AGND

1000 pF

Figure 22. Modem Connection

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