Cirrus Logic CS43L22 - Manual (Page 24)

24 DS792F2
CS43L22
Confidential Draft
3/4/10
4.3 Analog Passthrough
The CS43L22 accommodates analog routing of the analog input signal directly to the headphone amplifiers
by using the PASSTHRUx mux. This feature is useful in applications that utilize an FM tuner where audio
recovered over-the-air must be transmitted to the headphone amplifier directly. This analog passthrough
path reduces power consumption and is immune to modulator switching noise that could interfere with some
tuners.
Four analog input channels can be chosen or summed by using the PASSxSEL bits as shown in Figure 8
to provide input to the CS43L22 when in analog passthrough mode. A pair of passthrough amplifiers can be
used to mute and apply gain to the input signals.
Referenced Control Register Location
Analog Front End
PASSB=A ............................
ANLGSFTx ..........................
ANLGZCx ............................
PASSxSEL4,3,2,1 ................
PASSxMUTE .......................
PASSxVOL[7:0] ...................
PASSTHRUx........................
“Passthrough Channel B=A Gang Control” on page 42
“Ch. x Analog Soft Ramp” on page 42
“Ch. x Analog Zero Cross” on page 42
“Passthrough Input Channel Mapping” on page 42
“Passthrough Mute” on page 44
“Passthrough x Volume” on page 46
“Passthrough Analog” on page 44
AIN4B
AIN1B
AIN2B
AIN3B
ANALOG PASS
THRU TO
HEADPHONE
AMPLIFIER MUX
Σ
AIN4A
AIN1A
AIN2A
AIN3A
Σ
Analog Passthru
Amplifiers
ANLGSFTB
ANLGGZCB
PASSB=A
PASSBMUTE
PASSBVOL[7:0]
+12dB/-60dB
0.5 dB steps
ANLGSFTA
ANLGGZCA
PASSB=A
PASSAMUTE
PASSAVOL[7:0]
+12dB/-60dB
0.5 dB steps
PASSASEL[4:1]
PASSBSEL[4:1]
DAC A
Output
DAC B
Output
PASSTHRUA
PASSTHRUB
Figure 8. Analog Passthrough Signal Flow