Production Data
WM8945
LDO_VSEL [4:0]
LDO OUTPUT
Vref x 1.42
Vref x 1.50
Vref x 1.58
Vref x 1.66
Vref x 1.74
Vref x 1.82
Vref x 1.90
Vref x 1.97
Vref x 2.06
Vref x 2.13
Vref x 2.21
Vref x 2.29
Vref x 2.37
Vref x 2.45
Vref x 2.53
Vref x 2.69
LDO_VSEL [4:0]
LDO OUTPUT
Vref x 2.85
Vref x 3.00
Vref x 3.16
Vref x 3.32
Vref x 3.49
Vref x 3.63
Vref x 3.79
Vref x 3.95
Vref x 4.12
Vref x 4.28
Vref x 4.42
Vref x 4.58
Vref x 4.75
Vref x 4.90
Vref x 5.06
Vref x 5.23
00h
01h
02h
03h
04h
05h
06h
07h
08h
09h
0Ah
0Bh
0Ch
0Dh
0Eh
0Fh
10h
11h
12h
13h
14h
15h
16h
17h
18h
19h
1Ah
1Bh
1Ch
1Dh
1Eh
1Fh
Note – Vref is the applicable voltage reference, selected by LDO_REF_SEL.
Table 37 LDO Output Voltage Control
BG_VSEL [4:0]
BG Voltage (V)
BG_VSEL [4:0]
BG Voltage (V)
00h
01h
02h
03h
04h
05h
06h
07h
1.200
1.227
1.253
1.280
1.307
1.334
1.360
1.387
08h
09h
0Ah
0Bh
0Ch
0Dh
0Eh
0Fh
1.414
1.440
1.467
1.494
1.520
1.547
1.574
1.600
Table 38 Bandgap Voltage Control
REFERENCE VOLTAGES AND MASTER BIAS
This section describes the analogue reference voltage and bias current controls. It also describes the
VMID soft-start circuit for pop suppressed start-up and shut-down.
The analogue circuits in the WM8945 require a mid-rail analogue reference voltage, VMID. This
reference is generated via a programmable resistor chain. Together with the external decoupling
capacitor (connected to the VMIDC pin), the programmable resistor chain results in a slow, normal or
fast charging characteristic on the VMID reference. This is enabled using VMID_ENA and VMID_SEL.
The different resistor options controlled by VMID_SEL can be used to optimise the reference for
normal operation, low power standby or for fast start-up as described in Table 39.
The VMID resistor chain can be powered from the LDO output (LDOVOUT) or from the LDO supply
(LDOVDD). This is selected using VMID_REF_SEL.
Note that when VMID is selected as the LDO reference voltage, VMID cannot be generated from the
LDOVOUT supply voltage (VMID_REF_SEL = 1) and must be generated from the LDOVDD supply
voltage (VMID_REF_SEL = 0).
The VMID ratio can be selected using VMID_CTRL. This selects the ratio of VMID to the supply
voltage that has been selected by VMID_REF_SEL. VMID should be half of the LDOVOUT supply
voltage for maximum voltage swing. In the case where VMID_REF_SEL has selected the LDOVOUT
supply voltage output, then VMID_CTRL should select the ratio “1/2”. In the case where
VMID_REF_SEL has selected the LDOVDD supply voltage, then the alternate ratio “5/11” may be
preferred provided LDOVDDD = 3.3V and LDOVOUT = 3.0V.
PD, May 2011, Rev 4.1
61
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
