WM9090ECSSLASHR datasheet(43/81 Pages) WOLFSON

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Production Data

WM9090

PD, November 2010, Rev 4.1

POWER SEQUENCES AND POP SUPPRESSION CONTROL

The WM9090 incorporates a number of features, including Wolfson’s SilentSwitch™ technology,

designed to suppress pops normally associated with Start-Up, Shut-Down or signal path control. To

achieve maximum benefit from these features, careful attention is required to the sequence and

timing of these controls. Note that, under the recommended usage conditions of the WM9090, these

features will be configured by running the default Start-Up and Shut-Down sequences as described in

the “Control Write Sequencer” section. In these cases, the user does not need to set these register

fields directly. Additional bias controls, also pre-programmed into Control Write Sequencer, are

described in the “Reference Voltages and Master Bias” section.

INPUT VMID CLAMPS

The analogue inputs are biased to VMID in normal operation. In order to avoid audible pops caused

by enabling the inputs, the WM9090 can clamp the input pins to VMID when the relevant input stage

is disabled. This allows pre-charging of the input AC coupling capacitors during power-up.

The Input VMID Clamps connect the input pins to a buffered VMID reference. The buffered VMID

reference is enabled by setting VMID_BUF_ENA. The VMID Clamp is enabled on each pair of input

pins independently using the register bits defined in Table 23.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R22 (16h)

IN1 Line Control

IN1_CLAMP

IN1P and IN1N input pad VMID clamp

0 = Clamp de-activated

1 = Clamp activated

R23 (17h)

IN2 Line Control

IN2_CLAMP

IN2P and IN2N input pad VMID clamp

0 = Clamp de-activated

1 = Clamp activated

R57 (39h)

AntiPOP2

VMID_BUF_ENA

VMID Buffer Enable

0 = Disabled

1 = Enabled

Table 23 Input VMID Clamps

HEADPHONE ENABLE/DISABLE

The ground-referenced headphone outputs implement Wolfson’s SilentSwitch™ technology to

minimise pop noise associated with enabling and disabling. The output pins HPOUTL and HPOUTR

are shorted to GND by default while the individual driver stages are enabled. As a final step the short

circuit is

then removed on each of these paths by setting the applicable fields

HPOUT1L_RMV_SHORT and HPOUT1R_RMV_SHORT.

The ground-referenced Headphone output drivers are designed to suppress pops and clicks when

enabled or disabled. However, it is necessary to control the drivers in accordance with a defined

sequence in start-up and shut-down to achieve the pop suppression. It is also necessary to schedule

the DC Servo offset correction at the appropriate point in the sequence (see “DC Servo”). Table 24

and Table 25 describe the recommended sequences for enabling and disabling these output drivers.

SEQUENCE

HEADPHONE ENABLE

Step 1

HPOUT1L_ENA = 1

HPOUT1R_ENA = 1

Step 2

HPOUT1L_DLY = 1

HPOUT1R_DLY = 1

Step 3

DC offset correction

Step 4

HPOUT1L_OUTP = 1

HPOUT1L_RMV_SHORT = 1

HPOUT1R_OUTP = 1

HPOUT1R_RMV_SHORT = 1

Table 24 Headphone Output Enable Sequence

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