Pre-Production
WM8985
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
6:4
R2_2BOOSTVOL
000
Controls the R2 pin to the right
channel input boost stage:
000 = Path disabled
(disconnected)
001 = -12dB
010 = -9dB gain
011 = -6dB gain
100 = -3dB gain
101 = +0dB gain
110 = +3dB gain
111 = +6dB gain
Table 9 Input BOOST Stage Control
The BOOST stage is enabled under control of the BOOSTEN register bit.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R2 (02h)
4
BOOSTENL
0
0
Left channel Input BOOST enable
0 = Boost stage OFF
Power
management
2
1 = Boost stage ON
5
BOOSTENR
Right channel Input BOOST enable
0 = Boost stage OFF
1 = Boost stage ON
Table 10 Input BOOST Enable Control
MICROPHONE BIASING CIRCUIT
The MICBIAS output provides a low noise reference voltage suitable for biasing electret type
microphones and the associated external resistor biasing network. Refer to the Applications
Information section for recommended external components. The MICBIAS voltage can be altered via
the MBVSEL register bit. When MBVSEL=0, MICBIAS=0.9*AVDD1 and when MBVSEL=1,
MICBIAS=0.65*AVDD1. The output can be enabled or disabled using the MICBEN control bit.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R1 (01h)
4
MICBEN
0
Microphone Bias Enable
Power
management 1
0 = OFF (high impedance output)
1 = ON
Table 11 Microphone Bias Enable Control
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R44 (2Ch)
8
MBVSEL
0
Microphone Bias Voltage Control
0 = 0.9 * AVDD1
Input control
1 = 0.65 * AVDD1
Table 12 Microphone Bias Voltage Control
The internal MICBIAS circuitry is shown in Figure 18. Note that the maximum source current
capability for MICBIAS is 3mA. The external biasing resistors therefore must be large enough to limit
the MICBIAS current to 3mA.
PP, Rev 3.4, October 2006
37
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
