WM8912 datasheet(47/129 Pages) CIRRUS

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Production Data

WM8912

PD, Rev 4.1, February 2013

The Charge Pump is enabled by setting the CP_ENA bit. When enabled, the charge pump adjusts the

output voltages (CPVOUTP and CPVOUTN) as well as the switching frequency in order to optimise

the power consumption according to the operating conditions. This can take two forms, which are

selected using the CP_DYN_PWR register bit.



Dynamic control (CP_DYN_PWR = 1)

Under Register control, the HPOUTL_VOL, HPOUTR_VOL, LINEOUTL_VOL and LINEOUTR_VOL

Under Dynamic control, the audio signal level in the DAC is used to control the charge pump mode of

operation. This is the Wolfson ‘Class W’ mode, which allows the power consumption to be optimised

in real time.

Under the recommended usage conditions of the WM8912, the Charge Pump will be enabled by

running the default headphone Start-Up sequence as described in the “Control Write Sequencer”

section. (Similarly, it will be disabled by running the Shutdown sequence.) In these cases, the user

does not need to write to the CP_ENA bit. The Charge Pump operating mode defaults to Register

control; Dynamic control may be selected by setting the CP_DYN_PWR register bit, if appropriate.

Note that the charge pump clock is derived from internal clock SYSCLK; this may derived from MCLK

directly or else using the FLL output, as determined by the SYSCLK_SRC bit. Under normal

circumstances an external clock signal must be present for the charge pump to function. However,

the FLL has a free-running mode that does not require an external clock but will generate an internal

clock suitable for running the charge pump. The clock division from SYSCLK is handled transparently

by the WM8912 without user intervention, as long as SYSCLK and sample rates are set correctly.

Refer to the “Clocking and Sample Rates” section for more detail on the FLL and clocking

configuration.

The Charge Pump control fields are described in Table 30.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R98 (62h)

Charge

Pump 0

CP_ENA

Enable charge-pump digits

0 = disable

1 = enable

R104 (68h)

Class W (0)

CP_DYN_PWR

Enable dynamic charge pump power

control

0 = Charge pump controlled by

volume register settings (Class G)

1 = Charge pump controlled by real-

time audio level (Class W)

Class W is recommended for lowest

power consumption

Table 30 Charge Pump Control

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