WM8912 datasheet(38/129 Pages) CIRRUS

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WM8912

Production Data

PD, Rev 4.1, February 2013

OUTPUT SIGNAL PATHS ENABLE

The output PGAs for each analogue output pin can be enabled and disabled using the register bits

described in Table 23.

Note that the Headphone Outputs and Line Outputs are also controlled by fields located within

these signal paths. These registers are described in the following “Headphone / Line Output Signal

Paths Enable” section.

Under recommended usage conditions, all the control bits associated with enabling the Headphone

Outputs and the Line Outputs will be configured by scheduling the default Start-Up and Shutdown

sequences as described in the “Control Write Sequencer” section. In these cases, the user does not

need to set the register fields in R14, R15, R90 and R94 directly.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R14 (0Eh)

Power

Management 2

HPL_PGA_ENA

Left Headphone Output Enable

0 = disabled

1 = enabled

HPR_PGA_ENA

Right Headphone Output Enable

0 = disabled

1 = enabled

R15 (0Fh)

Power

Management 3

LINEOUTL_PGA_

ENA

Left Line Output Enable

0 = disabled

1 = enabled

LINEOUTR_PGA

_ENA

Right Line Output Enable

0 = disabled

1 = enabled

Table 23 Output Signal Paths Enable

Note that, to enable the output PGAs and multiplexers, the reference voltage VMID and the bias

current must also be enabled. See “Reference Voltages and Master Bias” for details of the associated

controls VMID_RES and BIAS_ENA.

HEADPHONE / LINE OUTPUT SIGNAL PATHS ENABLE

The 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 ground-referenced Headphone outputs and Line outputs are

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

applicable

fields

HPL_RMV_SHORT,

HPR_RMV_SHORT,

LINEOUTL_RMV_SHORT

LINEOUTR_RMV_SHORT.

The ground-referenced Headphone output and Line 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 24 and Table 25 describe the recommended sequences for enabling and

disabling these output drivers.

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