WM1811A datasheet(314/328 Pages) WOLFSON

314 / 328 page

WM1811A

Production Data

PD, November 2013, Rev 4.1

314

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 WM1811A.

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 applications, the use of ceramic capacitors with capacitor

dielectric X5R is recommended.

MICROPHONE BIAS CIRCUIT

The WM1811A is designed to interface easily with up to four analogue microphones. These may be

connected in single-ended or differential configurations, as illustrated in Figure 84. 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 analogue microphone requires a bias current (electret condenser

microphones) or voltage supply (silicon microphones), which can be provided by MICBIAS1 or

MICBIAS2.

A current-limiting resistor is 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 WM1811A is not exceeded. Wolfson

recommends a 2.2k

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

microphone models.

MIC

input

mixers

PGA

Line Input

VMID

IN1LN,

IN2LN,

IN1RN,

IN2RN

IN1LP,

IN2LP,

IN1RP,

IN2RP

MICBIAS1/2

2k2

AGND

2k2

Figure 84 Single-Ended and Differential Analogue Microphone Connections

The WM1811A also supports up to two digital microphone inputs. The MICBIAS1 generator is suitable

for use as a low noise supply for digital microphones, as shown in Figure 85.

WM1811A Datasheet(PDF) 314 Page - Wolfson Microelectronics plc

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