WM8993 datasheet(222/229 Pages) WOLFSON

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WM8993

Production Data

PD, November 2010, Rev 4.0

222

CHARGE PUMP COMPONENTS

A fly-back capacitor is required between the CPCA and CPCB pins. The required capacitance is

2.2μF at 2V.

A decoupling capacitor is required on CPVOUTP and CPVOUTN; the recommended value is 2.2μF

at 2V.

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

These capacitors should be placed as close as possible to the WM8994.

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. For most application the use of ceramic capacitors with capacitor

dielectric X5R is recommended.

MICROPHONE BIAS CIRCUIT

The WM8993 is designed to interface easily with up to four microphones. These may be connected

in single-ended or differential configurations. The single-ended method allows greater capability for

the connection of multiple audio sources simultaneously, whilst the differential method provides

better performance due to its rejection of common-mode noise.

In either configuration, the microphone requires a bias current (electret condenser microphones) or

voltage supply (silicon microphones), which can be provided by MICBIAS1 or MICBIAS2. These are

generated by identical output-compensated amplifiers, which require an external capacitor in order to

guarantee accuracy and stability. The recommended capacitance is 4.7

μF, although it may be

possible to reduce this to 1

μF if the analogue supply (AVDD1) is not too noisy. A ceramic type is a

suitable choice here, providing that care is taken to choose a component that exhibits this

capacitance at the intended MICBIAS voltage.

Note that the MICBIAS voltage may be adjusted using register control to suit the requirements of the

microphone. Also note the WM8993 supports a maximum current of 2.4mA per MICBIAS pin. If more

than one microphone is connected to a single MICBIAS pin, the combined current of these must not

exceed 2.4mA.

A current-limiting resistor is also required when using an electret condenser microphone (ECM). The

resistance should be chosen according to the minimum operating impedance of the microphone and

MICBIAS voltage so that the maximum bias current of the WM8993 is not exceeded. Wolfson

recommends a 2.2k

Ω current limiting resistor as it provides compatibility with a wide range of

microphone models.

Figure 87 illustrates the recommended single-ended and differential microphone connections for the

WM8993.

MIC

input

mixers

PGA

Line Input

VMID

IN1LN,

IN2LN,

IN1RN,

IN2RN

IN1LP,

IN2LP,

IN1RP,

IN2RP

MICBIAS1/2

2k2

4.7uF

AGND

Figure 87 Single-Ended and Differential Microphone Connections

WM8993 Datasheet(PDF) 222 Page - Wolfson Microelectronics plc

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