Cirrus Logic CS42L56 - Manual (Page 36)

36 DS851F2
CS42L56
4.2.5.1 Attack/Release Time Calculations:
The time taken by the ALC to perform an attack or a release operation is a function of the PGA/ADC digital
volume control gain settings, ADC soft ramp/zero-cross settings, sample rate (Fs), maximum/minimum
threshold settings, attack/release rate settings and the signal level after the digital volume control block.
Since the PGA and the ADC digital volume control blocks perform gain increment/decrement steps at dif-
ferent rates, this must be taken into account to get an accurate attack/release time duration calculation.
The attack and release rates for each block is determined by the formulas given below:
The maximum amount of time that can be taken by the ALC to perform an attack or release operation on
a signal with a specific maximum/minimum threshold, PGA gain and ADC digital volume setting is deter-
mined by the formulae below:
For attack operations:
For release operations:
Recommended settings: Best level control may be realized with a fast attack and a slow release setting
with soft ramp enabled in the control registers.
It should be noted that the ALC can only apply the gain up to the amount set in the PGAxVOL and ADCx-
ATT registers and that the ALC maintains the output signal between the ALCMIN and ALCMAX thresh-
olds. As a result when the input signal level changes, the level-controlled output may not always be the
same but will always fall within the thresholds.
4.3 Analog In to Analog Out Passthrough
The CS42L56 accommodates analog routing of the analog input signal directly to the headphone and line
out 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 an-
alog passthrough path reduces power consumption and is immune to modulator switching noise that could
interfere with some tuners. This path is selected using the Line and/or HP mux bits and powering down the
ADC.
Referenced Control Register Location
PGAxVOL[5:0] .....................
ADCxATT[7:0]......................
ALCMAX[2:0], ALCMIN[2:0]
ALCARATE[5:0]....................
ALCRRATE[5:0].................... “PGAx Volume” on page 78
“ADCx Volume” on page 78
“ALC Threshold (Address 24h)” on page 80
“ALC Enable & Attack Rate (Address 22h)” on page 79
“ALC Release Rate (Address 23h)” on page 79
Referenced Control Register Location
PDN_ADCx .........................
HPxMUX..............................
LINExMUX........................... “Power Down ADC x” on page 59
“Headphone Input Select” on page 83
“Line Input Select” on page 83
ADC Digital Volume Attack/Release Rate
1
16 ALCxRATE[5:0]

1 +
---------------------------------------------------------------- dB/LRCK =
PGA Attack/Release Rate
0.5
16 ALCxRATE[5:0]

1 +
---------------------------------------------------------------- dB/LRCK =
Maximum Attack Time
PGAxVOL[5:0] (-6) –
PGA Attack Rate   Fs

----------------------------------------------------------------
(-ALCMAX[2:0])
ADC Attack Rate   Fs

---------------------------------------------------------------- s + =
Maximum Release Time
ADCxATT[7:0] ALCMAX[2:0] –
ADC Release Rate   Fs

---------------------------------------------------------------------------------
PGAxVOL[5:0] (-6) –
PGA Release Rate   Fs

--------------------------------------------------------------------- s + =