WM8281 Datasheet, PDF (305/392 Pages) Cirrus Logic – Low Power Audio System with Ambient Noise Cancellation and Echo Cancellation

WM8281
CHARGE PUMPS, REGULATORS AND VOLTAGE REFERENCE
The WM8281 incorporates two Charge Pump circuits and two LDO Regulator circuits to generate
supply rails for internal functions and to support external microphone requirements. The WM8281 also
provides three MICBIAS generators which provide low noise reference voltages suitable for biasing
electret condenser (ECM) type microphones or powering digital microphones.
Refer to the “Applications Information” section for recommended external components.
CHARGE PUMPS AND LDO2 REGULATOR
Charge Pump 1 (CP1) is used to generate the positive and negative supply rails for the analogue
output drivers. CP1 is enabled automatically by the WM8281 when required by the output drivers.
Charge Pump 2 (CP2) powers LDO2, which provides the supply rail for analogue input circuits and for
the MICBIAS generators. CP2 and LDO2 are enabled using the CP2_ENA register bit.
The 32kHz clock must be configured and enabled when using CP2. See “Clocking and Sample Rates”
for details of the system clocks.
When CP2 and LDO2 are enabled, the MICVDD voltage can be selected using the LDO2_VSEL
control field. Note that, when one or more of the MICBIAS generators is operating in normal
(regulator) mode, then the MICVDD voltage must be at least 200mV greater than the highest selected
MICBIASn output voltage(s).
When CP2 and LDO2 are enabled, an internal bypass path may be selected, connecting the MICVDD
pin directly to the CPVDD supply. This path is controlled using the CP2_BYPASS register. Note that
the bypass path is only supported when CP2 is enabled.
When CP2 is disabled, the CP2VOUT pin can be configured to be floating or to be actively
discharged. This is selected using the CP2_DISCH register bit.
When LDO2 is disabled, the MICVDD pin can be configured to be floating or to be actively
discharged. This is selected using the LDO2_DISCH register bit.
The MICVDD pin is connected to the output of LDO2. Note that the MICVDD does not support direct
connection to an external supply; MICVDD is always powered internally to the WM8281.
The Charge Pumps and LDO2 Regulator circuits are illustrated in Figure 82. The associated register
control bits are descrbed in Table 125.
Note that decoupling capacitors and flyback capacitors are required for these circuits. Refer to the
“Applications Information” section for recommended external components.
Rev 4.0
305