WM8994 datasheet(111/359 Pages) WOLFSON

111 / 359 page

Production Data

WM8994

PD, April 2012, Rev 4.4

111

HEADPHONE SIGNAL PATHS ENABLE

The HPOUT1L and HPOUT1R 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 VMID reference voltage. This is also desirable in shutdown to prevent the

external connections from being affected by the internal circuits. The HPOUT1L and HPOUT1R

outputs are shorted to AGND by default; the short circuit is removed on each of these paths by setting

the applicable fields HPOUT1L_RMV_SHORT or 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 shutdown 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 54

and Table 55 describe the recommended sequences for enabling and disabling these output drivers.

SEQUENCE

HEADPHONE ENABLE

Step 1

HPOUT1L_ENA = 1

HPOUT1R_ENA = 1

Step 2

s delay

Step 3

HPOUT1L_DLY = 1

HPOUT1R_DLY = 1

Step 4

DC offset correction

Step 5

HPOUT1L_OUTP = 1

HPOUT1L_RMV_SHORT = 1

HPOUT1R_OUTP = 1

HPOUT1R_RMV_SHORT = 1

Table 54 Headphone Output Enable Sequence

SEQUENCE

HEADPHONE DISABLE

Step 1

HPOUT1L_RMV_SHORT = 0

HPOUT1L_DLY = 0

HPOUT1L_OUTP = 0

HPOUT1R_RMV_SHORT = 0

HPOUT1R_DLY = 0

HPOUT1R_OUTP = 0

Step 2

HPOUT1L_ENA = 0

HPOUT1R_ENA = 0

Table 55 Headphone Output Disable Sequence

The register bits relating to pop suppression control are defined in Table 56.

WM8994 Datasheet(PDF) 111 Page - Wolfson Microelectronics plc

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