WM8945ECSSLASHR datasheet(62/169 Pages) WOLFSON

62 / 169 page

WM8945

Production Data

PD, May 2011, Rev 4.1

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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R7 (07h)

Additional

control

VMID_REF_SEL

VMID Source Select

0 = LDO supply (LDOVDD)

1 = LDO output (LDOVOUT)

VMID_CTRL

VMID Ratio control

Sets the ratio of VMID to the source

selected by VMID_REF_SEL

0 = 5/11

1 = ½

VMID_ENA

VMID Enable

0 = Disabled

1 = Enabled

R2 (02h)

Power

Management

BIAS_ENA

Master Bias Enable

0 = Disabled

1 = Enabled

1:0

VMID_SEL [1:0]

VMID Divider Enable and Select

00 = VMID disabled (for OFF mode)

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.

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