Production Data
WM8912
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.
•
•
Register control (CP_DYN_PWR = 0)
Dynamic control (CP_DYN_PWR = 1)
Under Register control, the HPOUTL_VOL, HPOUTR_VOL, LINEOUTL_VOL and LINEOUTR_VOL
register settings are used to control the charge pump mode of operation.
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.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R98 (62h)
0
CP_ENA
0
Enable charge-pump digits
0 = disable
Charge
Pump 0
1 = enable
R104 (68h)
Class W (0)
0
CP_DYN_PWR
0
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
PD, Rev 4.0, September 2010
47
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
