lm4935rlx National Semiconductor Corporation, lm4935rlx Datasheet - Page 39

• Manufacturer Part Number: lm4935rlx
• Description: Audio Sub-system With Dual-mode Stereo Headphone And Mono High Efficiency Loudspeaker Amplifiers And Multi-purpose Adc
• Manufacturer: National Semiconductor Corporation

Bits
12.0 Status & Control Registers
12.17 MIC_2 CONFIGURATION REGISTER
This register is used to control the microphone configuration.
2:1
5:4
In OCL mode there is a trade-off between the external microphone supply voltage (EXT_MIC_BIAS - OCL_VCM_ VOLTAGE) and
the maximum output power possible from the headphones. A lower OCL_VCM_VOLTAGE gives a higher microphone supply
voltage but a lower maximum output power from the headphone amplifiers due to the lower OCL_VCM_VOLTAGE - A_V
0
3
2.9V to 3.4V
2.8V to 2.9V
2.7V to 2.8V
Available
A_V
>
BUTTON_TYPE
3.4V
DEBOUNCE_
VOLTAGE
VOLTAGE
BUTTON_
DD
VCM_
BIAS_
OCL_
MIC_
TIME
Field
Selects the voltage used as virtual ground (HP_VMID pin) in OCL mode. This will depend on the
available supply and the power output requirements of the headphone amplifiers.
Selects the voltage as a reference to the internal and external microphones. Only one bias pin is
driven at once depending on the INT_EXT bit setting found in the MIC_1 (0x0Bh) register.
MIC_BIAS_VOLTAGE should be set to ’11’ only if A_V
MIC_BIAS_VOLTAGE = ’00’ (EXT_BIAS = 2.0V) should not be used to generate the EXT_BIAS
supply for a cellular headset external microphone. Please refer to Table 18 for more detail.
If set the LM4935 assumes that the button (if used) in the headset is in series (series push button)
with the microphone, opening the circuit when pressed. The default is for the button to be in parallel
(parallel push button), shorting out the microphone when pressed.
Sets the time used for debouncing the pushing of the button on a headset with a parallel push
button.
EXT_MIC_BIAS
Recommended
OCL_VCM_VOLTAGE
MIC_BIAS_VOLTAGE
TABLE 18. External MIC Supply Voltages in OCL Mode
3.3V
2.8V
2.5V
2.5V
00
01
10
11
0
1
2
2
2
2
BUTTON_DEBOUNCE_TIME
TABLE 17. MIC_2 (0x0Ch)
(Continued)
00
01
10
OCL_VCM_VOLT = 1.5V
11
2
2
2
2
39
1.8V
1.3V
1.0V
-
Description
EXT_BIAS
2.0V
2.5V
2.8V
3.3V
Supply to Microphone
DD
>
3.4V. In OCL mode,
Voltage
1.2V
1.5V
OCL_VCM_VOLT = 1.2V
Time (ms)
INT_BIAS
2.1V
1.6V
1.3V
1.3V
2.0V
2.5V
2.8V
3.3V
16
32
0
8
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