WM8994ECSSLASHR datasheet(232/363 Pages) CIRRUS

232 / 363 page

WM8994

232

Rev 4.6

LINE OUTPUT DISCHARGE CONTROL

The line output paths can be actively discharged to AGND through internal resistors if desired. This is

desirable at start-up in order to achieve a known output stage condition prior to enabling the soft-start

VMID reference voltage. This is also desirable in shut-down to prevent the external connections from

being affected by the internal circuits.

The

line

outputs

LINEOUT1P

and

LINEOUT1N

are

discharged

AGND

setting

LINEOUT1_DISCH. The line outputs LINEOUT2P and LINEOUT2N are discharged to AGND by

setting LINEOUT2_DISCH.

The discharge resistance is dependent upon the respective LINEOUTn_ENA bit, and also according

to the VROI bit (see Table 132

). The discharge resistance is noted in the “Electrical Characteristics”

section.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R56 (0038h)

AntiPOP (1)

LINEOUT1_DISC

Discharges LINEOUT1P and

LINEOUT1N outputs

0 = Not active

1 = Actively discharging LINEOUT1P

and LINEOUT1N

LINEOUT2_DISC

Discharges LINEOUT2P and

LINEOUT2N outputs

0 = Not active

1 = Actively discharging LINEOUT2P

and LINEOUT2N

Table 133 Line Output Discharge Control

VMID REFERENCE DISCHARGE CONTROL

The VMID reference can be actively discharged to AGND through internal resistors. This is desirable

at start-up in order to achieve a known initial condition prior to enabling the soft-start VMID reference;

this ensures maximum suppression of audible pops associated with start-up. VMID is discharged by

setting VMID_DISCH.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R57 (0039h)

AntiPOP (2)

VMID_DISCH

Connects VMID to ground

0 = Disabled

1 = Enabled

Table 134 VMID Reference Discharge Control

INPUT VMID CLAMPS

The analogue inputs can be clamped to Vmid using the INPUTS_CLAMP bit described below. This

allows pre-charging of the input AC coupling capacitors during power-up. Note that all eight inputs are

clamped using the same control bit.

Note that INPUTS_CLAMP must be set to 0 when the analogue input signal paths are in use.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R21 (15h)

Input Mixer (1)

INPUTS_CLAMP

Input pad VMID clamp

0 = Clamp de-activated

1 = Clamp activated

Table 135 Input VMID Clamps

WM8994ECS/R 数据表(PDF) 232 Page - Cirrus Logic

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