wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 59

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

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Pre-Production
REFERENCE VOLTAGES
All internal analogue input and output circuitry requires a reference voltage AVDD/2 (VMID). This
voltage is generated internally using 6.8kΩ, 50kΩ or 300kΩ (+/- 15%) resistors and is buffered as
required. These functions are controlled using register bits VMID_MODE and VREF_ENA.
Table 20 Reference Voltages
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 MIC1BIAS_ENA
control bit and the voltage can be selected using the MBSEL register bit as detailed in Table 21.
Table 21 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 65- see “General Purpose Input/Output” for a full
description of these fields. Note that the MICBIAS current thresholds are subject to a wide tolerance -
up to +/-50% of the specified value.
REGISTER
ADDRESS
R2 (02h)
R2 (02h)
R58 (3Ah)
REGISTER
ADDRESS
4
0
BIT
2:1
0
BIT
MIC1BIAS_ENA
(rw)
MBSEL
VMID_MODE
[1:0]
(rw)
VREF_ENA
(rw)
LABEL
LABEL
00b
0b
DEFAULT
DEFAULT
0b
0b
VMID Divider Enable and Select
00 = VMID disabled (for OFF mode)
01 = 2 x 50kΩ divider (Normal mode)
10 = 2 x 300kΩ divider (Standby mode)
11 = 2 x 6.8kΩ divider (for fast start-up)
VREF Enable (Bias for all analogue
functions)
0 = VREF bias disabled
1 = VREF bias enabled
Microphone Bias
0 = OFF (high impedance output)
1 = ON
Microphone Bias Voltage Control
0 = 0.9 * AVDD
1 = 0.65 * AVDD
DESCRIPTION
DESCRIPTION
PP, April 2009, Rev 3.0
WM8400
59