wm8595 Wolfson Microelectronics plc, wm8595 Datasheet - Page 33

• Manufacturer Part Number: wm8595
• Description: 24-bit 192khz 2vrms Multi-channel Codec
• Manufacturer: Wolfson Microelectronics plc

Production Data
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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:
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
Table 23 Analogue Volume Ramp Rate
SAMPLE RATE FOR PGA (kHz)
176.4
44.1
88.2
192
32
48
96
DIVIDE BY
16
16
32
32
8
8
8
PGA RAMP RATE
(ms/dB)
0.50
0.36
0.33
0.36
0.33
0.36
0.33
PD, Rev 4.1, April 2010
WM8595
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