ALC250 Data Sheet
9.8 DC Voltage Volume Control
The ALC250 has a 32-step internal volume control that is controlled by the DC voltage applied the ‘DC Vol’ pin (pin-32). The
volume control input range is from GND to AVDD, to attenuate the master volume (real MX02), headphone volume (real
MX04) and mono-out volume (real MX06). A higher DC voltage means more attenuation related to output volume. The table
below shows the relation between input DC voltage and the 5-bit volume code.
Input DC Volume
Note
Input DC Volume
Note
Voltage
Code
Voltage
Code
95%=< DC
1F
DCMute=1 47%< DC <= 50% F
92%< DC <= 95% 1E
DCMute=0 44%< DC <= 47% E
89%< DC <= 92% 1D
41%< DC <= 44% D
86%< DC <= 89% 1C
38%< DC <= 41% C
83%< DC <= 86% 1B
35%< DC <= 38% B
80%< DC <= 83% 1A
32%< DC <= 35% A
77%< DC <= 80% 19
29%< DC <= 32% 9
74%< DC <= 77% 18
26%< DC <= 29% 8
71%< DC <= 74% 17
23%< DC <= 26% 7
68%< DC <= 71% 16
20%< DC <= 23% 6
65%< DC <= 68% 15
17%< DC <= 20% 5
62%< DC <= 65% 14
14%< DC <= 17% 4
59%< DC <= 62% 13
11%< DC <= 14% 3
56%< DC <= 59% 12
8%< DC <= 11% 2
53%< DC <= 56% 11
5%< DC <= 8% 1
50%< DC <= 53% 10
DC <= 5%
0
DCMute=0
Input DC Voltage is ratio of AVDD (+5VA).
❷This 5-bit volume code adds extra attenuation for master volume and headphone volume, the absolute maximum volume is
determined by MX02, MX04 and MX06.
Once the sum of MX value and volume code exceeds 3Fh, the real MX value is 3Fh.
Example 1: (Normal case)
MX02=0002h, MX04=0300h, MX06=0001h, Volume Code=2h,
then Master Volume=0204h, Headphone Volume=0502h, Mono-Out=0003h
Example 2: (The sum exceeds 3Fh for MX02/MX04, 1Fh for MX06)
MX02=2F2Fh, MX04=2E2Eh, MX06=0002h, Volume Code=1Eh,
then Master Volume=3F3Fh, real Headphone Volume=3D3Dh, Mono-Out=001Fh
Example 3: (Volume code is 1Fh, DCMute=1, real MXs should be muted)
MX02=0000h, MX04=2020h, MX06=0010h, Volume Code=1Fh,
then Master Volume=9F1Fh, Headphone Volume=BF3Fh, Mono-Out=801Fh
Two Channel AC’97 2.3 Audio Codec
37
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