WM8945
Production Data
Note that the “5/11” ratio is designed for the case where LDOVDD = 3.3V and LDOVOUT = 3.0V. This
results in a VMID = 3.3V x (5/11) = 1.5V which is half of the LDOVOUT voltage.
If these conditions are not being used or the LDO has been bypassed then VMID_REF should be set
to select LDOVOUT as the VMID source and VMID_CTRL should be set to select the ratio “1/2”.
The analogue circuits in the WM8945 require a bias current. The normal bias current is enabled by
setting BIAS_ENA. Note that the normal bias current source requires VMID to be enabled also.
The Master Reference and Bias Control bits are defined in Table 39.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R7 (07h)
VMID_REF_SEL
VMID Source Select
10
0
Additional
control
0 = LDO supply (LDOVDD)
1 = LDO output (LDOVOUT)
VMID Ratio control
VMID_CTRL
9
0
Sets the ratio of VMID to the source
selected by VMID_REF_SEL
0 = 5/11
1 = ½
VMID_ENA
VMID Enable
4
3
0
0
0 = Disabled
1 = Enabled
R2 (02h)
BIAS_ENA
Master Bias Enable
0 = Disabled
Power
Management
1
1 = Enabled
VMID_SEL [1:0]
VMID Divider Enable and Select
00 = VMID disabled (for OFF mode)
1:0
00
01 = 2 x 50k divider (for normal
operation)
10 = 2 x 250k divider (for low
power standby)
11 = 2 x 5k divider (for fast start-
up)
Table 39 Reference Voltages and Master Bias Enable
A pop-suppressed start-up requires VMID to be enabled smoothly, without the step change normally
associated with the initial stage of the VMID capacitor charging. A pop-suppressed start-up also
requires the analogue bias current to be enabled throughout the signal path prior to the VMID
reference voltage being applied. The WM8945 incorporates pop-suppression circuits which address
these requirements.
PD, May 2011, Rev 4.1
62
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
