Production Data
WM8352
13.12.3 MID-RAIL REFERENCE (VMID)
VMID provides a potential mid-way between AVDD and GND, used in many parts of the audio
CODEC. It is generated from AVDD using on-chip potential dividers. Different resistor values can be
selected for this purpose. A medium resistance should be used when the CODEC is active. A high
resistance option provides a more power-efficient way to maintain the VMID voltage when the
CODEC is in “Standby” (i.e. inactive but ready to start immediately, without needing to wait for the
VMID capacitor to be charged). For startup and shutdown the VMID generator provides soft VMID
ramping to reduce pops and clicks. The speed of this ramp is selectable using the anti-pop controls
and can be tuned to the application.
Figure 62 Generating the Mid-rail Reference
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
Enables VMID resistor string
0 = disabled
R8 (08h)
2
VMID_EN
A
0
Power
Management 1
1 = enabled
1:0
VMID [1:0]
00
Resistor selection for VMID potential divider
00 = off
(off)
01 = Vmid comes from 300kΩ R-string
10 = Vmid comes from 50kΩ R-string
11 = Vmid comes from 5kΩ R-string
Table 50 Controlling the Mid-rail Reference
PD, February 2011, Rev 4.4
101
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
