CS42L52 datasheet(32/82 Pages) CIRRUS

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DS680A1

CS42L52

4.4

Analog In to Analog Out Passthru

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 passthru

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 how this

ADC power-down override functions in accord with the state of the speaker channels. The shaded cells

represent normal ADC operation when passthru is disabled.

When PASSTHRU and PDN_OVRD are enabled, turning the speaker channel ON (by writing ‘11’b to

SPKx_PDN[1:0] or by automatic activation of the headphone detect switch, SPK/HP_SW) will automati-

cally 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

Powered UP

Powered DOWN

OFF

Powered DOWN

Powered UP

MA X [2 :0 ]

O u tput

(a fter Lim ite r)

In p u t

RRAT E[5 :0 ]

ARAT E[5 :0 ]

Vo lu m e

Lim ite r

C U S H [2 :0 ]

AT T ACK/RE L E A S E SOU N D

CUS H IO N

MA X [2 :0 ]

Figure 14. Peak Detect & Limiter

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