WM8595 datasheet(33/82 Pages) WOLFSON

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Production Data

WM8595

PD, Rev 4.2, January 2011

VOLUME RAMP

Analogue volume can be adjusted by step change or by soft ramp. The ramp rate is dependent upon

the sampling rate. The sampling rate upon which the volume ramp rate is based can be selected

between the DAC sampling rate or the ADC sampling rate in either slave mode or master mode. The

ramp rates for common audio sample rates are shown in Table 23:

SAMPLE RATE FOR PGA (kHz)

DIVIDE BY

PGA RAMP RATE

(ms/dB)

0.50

44.1

0.36

0.33

88.2

0.36

0.33

176.4

0.36

192

0.33

Table 23 Analogue Volume Ramp Rate

For example, when using a sample rate of 48kHz, the time taken for a volume change from and initial

setting of 0dB to -20dB is calculated as follows:

Volume Change (dB) x PGA Ramp Rate (ms/dB) = 20 x 0.33 = 6.6ms

When changing from one PGA ramp clock source to another, it is recommended that

PGA_SAFE_SW is set to 0. This forces the clock switch over to occur at a point where all relevant

clock signals are zero, ensuring glitch-free operation. This process can take up to 32 left/right clock

cycles.

If a faster change in PGA ramp rate clock source is required, PGA_FORCE can be set to 1. This

forces the change in clock source to occur immediately regardless of the state of the relevant clock

signals internally. Glitch-free operation is not guaranteed under these conditions. PGA_FORCE

must be set back to 0 to initialise the timing circuits with the new clock.

If the volume ramp function is not required when increasing or decreasing volume, this block can be

bypassed by setting ATTACK_BYPASS or DECAY_BYPASS to 1. Figure 19 shows the effect of

these register settings:

Figure 19 ATTACK_BYPASS and DECAY_BYPASS Functionality

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