Cirrus Logic CS42L52 - Manual (Page 31)

DS680F2 31
CS42L52
3/1/13
4.4 Analog In to Analog Out Passthrough
The CS42L52 accommodates analog routing of the analog input signal directly to the headphone amplifiers.
This feature is useful in applications that utilize an FM tuner where audio recovered over-the-air must be
transmitted to the headphone amplifier without digital conversion in the ADC and DAC. This analog
passthrough path reduces power consumption and is immune to modulator switching noise that could
interfere with some tuners.
4.4.1 Overriding the ADC Power Down
To accommodate automatic activation of the speaker amplifier when the SPK/HP_SW switch pin chang-
es, the CS42L52 provides the option to automatically power up the ADC whenever the analog signal must
route to the digital PWM modulator, regardless of the PDN_ADC bit. Refer to the table below for details
on how this ADC power-down override functions in accordance with the state of the speaker channels.
The shaded cells represent normal ADC operation when passthrough is disabled.
When PASSTHRU and PDN_OVRD are enabled, turning the speaker channel ON (by writing ‘11’b to SP-
Kx_PDN[1:0] or by automatic activation of the headphone detect switch, SPK/HP_SW) will automatically
disable the ADCx_PDN in order to convert the analog input to a digital signal for the PWM modulator. This
allows automatic analog input routing to the speaker amplifiers.
PDN_ADC PASSTHRU PDN_OVRD Speaker Channel ADC Status
0 x x x Powered UP
1
0 x x Powered DOWN
1
0 x Powered DOWN
1
OFF Powered DOWN
ON Powered UP
M A X [2 :0 ]
O u tp u t
(a fte r L im ite r)
In p u t
R R A T E [5 :0 ] A R A T E [5 :0 ]
V o lu m e
L im ite r
C U S H [2 :0 ]
A T T A C K /R E L E A S E S O U N D
C U S H IO N
M A X [2 :0 ]
Figure 14. Peak Detect and Limiter