Pre-Production
WM8959
MICROPHONE BIAS CONTROL
The MICBIAS output provides a low noise reference voltage suitable for biasing electret type
microphones via an external resistor. Refer to the Applications Information section for recommended
external components. The MICBIAS voltage can be enabled or disabled using the MICBIAS_ENA
control bit and the voltage can be selected using the MBSEL register bit as detailed in Table 3.
REGISTER BIT
ADDRESS
LABEL
DEFAULT
DESCRIPTION
R1 (01h)
4
MICBIAS_ENA
(rw)
0b
Microphone Bias
0 = OFF (high impedance output)
1 = ON
R58 (3Ah)
0
MBSEL
0b
Microphone Bias Voltage Control
0 = 0.9 * AVDD
1 = 0.65 * AVDD
Table 3 Microphone Bias Control
Note that the maximum source current capability for MICBIAS is 3mA. The external biasing
resistance must be large enough to limit the MICBIAS current to 3mA.
MICROPHONE CURRENT DETECT
A MICBIAS current detect function allows detection of accessories such as headset microphones.
When the MICBIAS load current exceeds one of two programmable thresholds, (e.g. short circuit
current or normal operating current), an interrupt or GPIO output can be generated. The current
detection circuit is enabled by the MCD bit; the current thresholds are selected by the MCDTHR and
MCDSCTH register fields as described in Table 41 - see “General Purpose Input/Output” for a full
description of these fields.
PP, May 2008, Rev 3.1
39
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
