WM8994ECSSLASHR datasheet(134/363 Pages) CIRRUS

134 / 363 page

WM8994

134

Rev 4.6

CHARGE PUMP

The WM8994 incorporates a dual-mode Charge Pump which generates the supply rails for the

headphone output drivers, HPOUT1L and HPOUT1R.

The Charge Pump has a single supply input, CPVDD, and generates split rails CPVOUTP and

CPVOUTN according to the selected mode of operation.

The Charge Pump connections are illustrated in Figure 32

(see “Applications Information” for external

component values). An input decoupling capacitor may also be required at CPVDD, depending upon

the system configuration.

CPVDD

Charge Pump

CPVOUTP

CPVOUTN

CPCA

CPCB

CPGND

Figure 32 Charge Pump External Connections

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 HPOUT1L_VOL and HPOUT1R_VOL register settings are used to control

the charge pump mode of operation.

Under Dynamic control, the audio signal level in the digital audio interface is used to control the

charge pump mode of operation. The CP_DYN_SRC_SEL register determines which of the digital

signal paths is used for this function - this may be AIF1 Timeslot 0, AIF Timeslot 1 or AIF2. The

CP_DYN_SRC_SEL should be set according to the active source for the HPOUT1L and HPOUT1R

outputs.

The Dynamic

Charge Pump Control mode is the Wolfson ‘Class W’ mode, which allows the power

consumption to be optimised in real time, but can only be used if a single AIF source is the only signal

source. The Class W mode should not be used if any of the bypass paths are used to feed analogue

inputs into the output signal path, or if more than one AIF source is used to feed the headphone

output via the Digital Mixers.

Under the recommended usage conditions of the WM8994, 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 Shut-Down 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.

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