WM8281ECSSLASHR datasheet(380/392 Pages) CIRRUS

380 / 392 page

WM8281

380

Rev 4.0

CHARGE PUMP COMPONENTS

The WM8281 incorporates two Charge Pump circuits, identified as CP1 and CP2.

CP1 generates the CP1VOUTP and CP1VOUTN supply rails for the ground-referenced headphone

drivers; CP2 generates the CP2VOUT supply rail for the microphone bias (MICBIAS) regulators.

Decoupling capacitors are required on each of the Charge Pump outputs. Two fly-back capacitors are

required for CP1; a single fly-back capacitor is required for CP2.

The recommended Charge Pump capacitors for WM8281 are detailed below in Table 133.

DESCRIPTION

CAPACITOR

CP1VOUT1P decoupling

Required capacitance is 2.0

F at 2V.

Suitable component typically 4.7

F.

CP1VOUT1N decoupling

Required capacitance is 2.0

F at 2V.

Suitable component typically 4.7

F.

CP1 fly-back 1

(connect between CP1C1A and CP1C1B)

Required capacitance is 1.0

F at 2V.

Suitable component typically 2.2

F.

CP1VOUT2P decoupling

Required capacitance is 2.0

F at 2V.

Suitable component typically 4.7

F.

CP1VOUT2N decoupling

Required capacitance is 2.0

F at 2V.

Suitable component typically 4.7

F.

CP1 fly-back 2

(connect between CP1C2A and CP1C2B)

Required capacitance is 1.0

F at 2V.

Suitable component typically 2.2

F.

CP2VOUT decoupling

Required capacitance is 1.0

F at 3.6V.

Suitable component typically 4.7

F.

CP2 fly-back

(connect between CP2CA and CP2CB)

Required capacitance is 220nF at 2V.

Suitable component typically 470nF.

Table 133 Charge Pump External Capacitors

Ceramic capacitors are recommended for these Charge Pump requirements. Note that, due to the

wide tolerance of many types of ceramic capacitors, care must be taken to ensure that the selected

components provide the required capacitance across the required temperature and voltage ranges in

the intended application. Ceramic capacitors with X5R dielectric are recommended.

The positioning of the Charge Pump capacitors is important, particularly the fly-back capacitors.

These capacitors should be placed as close as possible to the WM8281. The component choice and

positioning of the CP1 components are more critical than those of CP2, due to the higher output

power requirements of CP1.

EXTERNAL ACCESSORY DETECTION COMPONENTS

The external accessory detection circuit measures jack insertion using the JACKDET pin. The

insertion switch status is detected using an internal pull-up resistor circuit on the JACKDET pin.

Microphone detection and key-button press detection is supported using the MICDETn pins. The

applicable pin should be connected to one of the MICBIASn outputs, via a 2.2k

 bias resistor, as

described in the “Microphone Bias Circuit” section. Note that, when using the External Accessory

Detection function, the MICBIASn resistor must be 2.2k

 +/-2%.

A recommended circuit configuration, including headphone output on HPOUT1 and microphone

connections, is shown in Figure 93

. See “Analogue Input Paths” for details of the DC-blocking

microphone input capacitor selection.

The recommended external components and connections for microphone / push-button detection are

illustrated in Figure 94.

Note that, when using the Microphone Detect circuit, it is recommended to use one of the Right

channel analogue microphone input paths, to ensure best immunity to electrical transients arising

from the external accessory.

WM8281ECS/R Datenblatt(PDF) 380 Page - Cirrus Logic

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