WM8599SEFTSLASHV datasheet(32/74 Pages) WOLFSON

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WM8599

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PP Rev 1.0 January 2007

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 24:

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 24 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_SAFE_SW 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.

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 16 shows the effect of

these register settings:

Figure 16 ATTACK_BYPASS and DECAY_BYPASS functionality

Note: When ATTACK_BYPASS=1 or DECAY_BYPASS=1, it is recommended that the zero cross

function for the PGA is used to eliminate click noise when changing volume settings.

WM8599SEFT/V Datasheet(PDF) 32 Page - Wolfson Microelectronics plc