TLC320AD75 Datasheet, PDF (20/43 Pages) Texas Instruments – 20-Bit Sigma-Delta Stereo ADA Circuit

2.14 DAC Digital Attenuation/Soft Mute
A value selected in the internal attenuation register determines the attenuation of the digital-audio data input.
The attenuation value is 12 bits long with a valid range of hex values from 400h to 000h. A data value of 001h
corresponds to an attenuation value of – 60 dB and a data value of 400h corresponds to 0 dB. The
attenuation function is nonlinear. Figure 2–9 illustrates the attenuation function in dB. The default
+ ǒ Ǔ ^{attenuation value is 400h (refer to the attenuator mode register for more detailed description).}
Attenuation
20 log
attenuation data
1024
0
– 10
– 20
– 30
– 40
– 50
– 60
1024 896 768 640 512 384 256 128 0
Attenuation Data (decimal values)
Figure 2–9. Digital Attenuation Characteristics
The attenuation operation of the DAC has a tapered gain response. It takes time T = 1024/f_s(sec) to reach
the actual 000H data output after an ATT = 000H data transfer from 400H data as shown in Figure 2–10.
400H
200H
Output Level (ATT)
000H
(Soft Mute)
T
ATT = 000H
Transfer
T
ATT = 400H
Transfer
T = 1024/fs (sec)
Figure 2–10. DAC Digital Attenuation Operation with Tapered Gain Response
2–8