WM8281ECSSLASHR datasheet(305/392 Pages) CIRRUS

305 / 392 page

WM8281

Rev 4.0

305

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.

WM8281ECS/R Datenblatt(PDF) 305 Page - Cirrus Logic