Rainbow Electronics MAX9867 - Manual (Page 38)

MAX9867
Ultra-Low Power Stereo Audio Codec
38 ______________________________________________________________________________________
Table 11. Playback Volume Registers (continued)
Microphone Inputs
Two differential microphone inputs and a low-noise micro-
phone bias for powering the microphones are provided
by the MAX9867. In typical applications, the left micro-
phone records a voice signal and the right microphone
records a background noise signal. In applications that
require only one microphone, use the left microphone
input and disable the right ADC. The microphone signals
are amplified by two stages of gain and then routed to
the ADCs. The first stage offers selectable 0dB, 20dB,
or 30dB settings. The second stage is a programmable
gain amplifier (PGA) adjustable from 0dB to 20dB in
1dB steps. Zero-crossing detection is included on the
PGA to minimize zipper noise while making gain
changes. See Figure 5 for a detailed diagram of the
microphone input structure. Table 12 is the microphone
input register.
Table 12. Microphone Input Register
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
REGISTER
ADDRESS
Left Microphone Gain 0 PALEN PGAML 0x12
Right Microphone Gain 0 PAREN PGAMR 0x13
BITS FUNCTION
VOLLM/VOLRM
Left/Right Playback Mute
VOLLM and VOLRM mute both the DAC and line input audio signals.
0 = Audio playback is unmuted.
1 = Audio playback is muted
Note: VSEN has no effect on the mute function. When VOLLM or VOLRM is set, the output is muted
immediately (ZDEN = 1) or at the next zero-crossing (ZDEN = 0).
Left/Right Playback Volume
VOLL and VOLR control the playback volume for both the DAC and line input audio signals.
SETTING GAIN (dB) SETTING GAIN (dB) SETTING GAIN (dB)
0x00 +6 0x0E -5 0x1C -42
0x01 +5.5 0x0F -6 0x1D -46
0x02 +5 0x10 -8 0x1E -50
0x03 +4.5 0x11 -10 0x1F -54
0x04 +4 0x12 -12 0x20 -58
0x05 +3.5 0x13 -14 0x21 -62
0x06 +3 0x14 -16 0x22 -66
0x07 +2 0x15 -18 0x23 -70
0x08 +1 0x16 -20 0x24 -74
0x09 0 0x17 -22 0x25 -78
0x0A -1 0x18 -26 0x26 -82
0x0B -2 0x19 -30 0x27 -84
0x0C -3 0x1A -34
0x0D -4 0x1B -38
0x28 to 0x3F MUTE
VOLL/VOLR
Note: Gain settings apply when the headphone amplifier is configured in differential mode. In the single-
ended and capacitorless modes, the actual gain is 5dB lower for each setting.