CS4294SLASHCS4298 datasheet(64/81 Pages) CIRRUS

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CS4205

DS489PP4

12. ANALOG HARDWARE

DESCRIPTION

The analog input section consists of four stereo

line-level

inputs

(LINE_L/R,

CD_L/GND/R,

VIDEO_L/R, and AUX_L/R), two selectable

mono microphone inputs (MIC1 and MIC2), and

two mono inputs (PC_BEEP and PHONE). The an-

alog output section consists of a mono output

(MONO_OUT) and a stereo line-level output

(LINE_OUT_L/R). This section describes the ana-

log hardware needed to interface with these pins.

The designs presented in this section are compliant

with Chapter 17 of Microsoft’s® PC 99 System De-

sign Guide [7] (referred to as PC 99) and Chapter

11 of Microsoft’s® PC 2001 System Design Guide

[8] (referred to as PC 2001). For information on

EMI reduction techniques refer to the application

note AN165: CS4297A/CS4299 EMI Reduction

Techniques [5].

12.1

Analog Inputs

All analog inputs to the CS4205, including

CD_GND, should be capacitively coupled to the

input pins. Unused analog inputs should be tied to-

gether and connected through a capacitor to analog

ground or tied to the Vrefout pin directly. The max-

imum allowed voltage for analog inputs, except the

microphone input, is 1 VRMS. The maximum al-

lowed voltage for the microphone input depends on

the selected boost setting.

12.1.1

Line Inputs

Figure 25 shows circuitry for a line-level stereo in-

put. Replicate this circuit for the Video and Aux in-

puts. This design attenuates the input by 6 dB,

bringing the signal from the PC 99 specified

2VRMS, to the CS4205 maximum allowed 1 VRMS.

12.1.2

CD Input

The CD line-level input has an extra pin,

CD_GND, providing a pseudo-differential input

for both CD_L and CD_R. This pin takes the

common-mode noise out of the CD inputs when

connected to the CD analog source ground. Follow-

ing the reference designs in Figure 26 and

Figure 27 provides extra attenuation of common

mode noise coming from the CD-ROM drive,

thereby producing a higher quality signal. One per-

cent resistors are recommended since closely

matched resistor values provide better com-

mon-mode attenuation of unwanted signals. The

circuit shown in Figure 26 can be used to attenuate

a 2 VRMS CD input signal by 6 dB. The circuit

shown in Figure 27 can be used for a 1 VRMS CD

input signal.

LINE_IN_R

LINE_IN_L

6.8 k

Ω

1.0

µ F

1.0

µ F

AGND

6.8 k

Ω

6.8 k

Ω

6.8 k

Ω

Figure 25. Line Input (Replicate for Video and AUX)

(All resistors 1%)

6.8 k

Ω

CD_L

CD_COM

CD_R

1.0

µF

CD_L

CD_R

CD_GND

6.8 k

Ω

1.0

µF

3.4 k

Ω

6.8 k

Ω

2.2

µF

3.4 k

Ω

6.8 k

Ω

AGND

Figure 26. Differential 2 V

RMS CD Input

100

Ω

CD_L

CD_COM

CD_R

1.0

µF

CD_L

CD_R

CD_GND

100

Ω

1.0

µF

100

Ω

47 k

Ω

2.2

µF

47 k

Ω

47 k

Ω

AGND

Figure 27. Differential 1 V

RMS CD Input

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