WM9090ECSSLASHR datasheet(52/81 Pages) WOLFSON

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WM9090

Production Data

PD, November 2010, Rev 4.1

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 WM9090 require a mid-rail analogue reference voltage, VMID. This

reference is generated from AVDD 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 VMID.

VMID is enabled by setting the VMID_ENA register bit. The programmable resistor chain is

configured by VMID_RES [1:0], and can be used to optimise the reference for normal operation, low

power standby or for fast start-up as described in Table 31.

When VMID is enabled using VMID_ENA, the WM9090 automatically controls VMID using a pop-

suppression circuit to avoid a step change in VMID; this suppresses pop/click noise which could

otherwise occur.

By default, the 2 x 5k

Ω VMID divider is selected in order to allow fast start-up. For normal operation

and lower power consumption, the VMID_RES register should be updated after start-up to select

another resistor value.

The analogue circuits in the WM9090 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.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R1 (01h)

Power

Management

(1)

2:1

VMID_RES

[1:0]

VMID Divider Enable and Select

00 = VMID disabled (for OFF mode)

01 = 2 x 50k

Ω divider (for normal operation)

10 = 2 x 250k

Ω divider (for low power standby)

11 = 2 x 5k

Ω divider (for fast start-up)

BIAS_ENA

Enables the Normal bias current generator (for

all analogue functions)

0 = Disabled

1 = Enabled

R57 (39h)

AntiPOP2

VMID_ENA

Enable VMID master bias current source

0 = Disabled

1 = Enabled

Table 31 Reference Voltages and Master Bias Enable

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