LM4931 datasheet(44/47 Pages) NSC

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Application Information (Continued)

toggled into and out of rapidly and is ideal for saving power

whenever continuous audio is not a requirement. All other

part functions are suspended.

Mono Speaker Mode (0010b)

Part is active. All analog outputs are biased. Audio from the

voiceband codec is routed to the mono speaker out. Stereo

headphone out is muted.

Headphone Call Mode (0011b)

Part is active. All analog outputs are biased. Audio from

voiceband codec is routed to the stereo headphones. Both

left and right channels are the same. Mono speaker out is

muted.

Conference Call Mode (0100b)

Part is active. All analog outputs are biased. Audio from the

voiceband codec is routed to the mono speaker out and to

the stereo headphones.

L+R Mixed to Mono Speaker (0101b)

Part is active. All analog outputs are biased. Full-range audio

from the 18bit/48kHz audio DAC is mixed together and

routed to the mono speaker out. Stereo headphones are

muted.

Headphone Stereo Audio (0110b)

Part is active. All analog outputs are biased. Full-range audio

from the 18bit/48kHz audio DAC is sent to the stereo head-

phone jack. Each channel is heard discretely. The mono

speaker is muted.

L+R Mixed to Mono Speaker + Stereo Headphone

Audio (0111b)

Part is active. All analog outputs are biased. Full-range audio

from the 18bit/48kHz audio DAC is sent discretely to the

stereo headphone jack and also mixed together and sent to

the mono speaker out.

Mixed Mode (1000b)

Part is active. All analog outputs are biased. This provides

one channel (the left channel) of full range audio to the mono

speaker out. Audio from the voiceband codec is then sent to

the stereo headphones, the same on each channel.

Mixed Mode (1001b)

Part is active. All analog outputs are biased. Mixed voice-

band and full-range audio (left channel only) is sent to the

mono speaker out. Audio from the voiceband codec only is

sent to the stereo headphones, the same on each channel.

Mixed Mode (1010b)

Part is active. All analog outputs are biased. Audio from the

voiceband codec is sent to the mono speaker out. The left

channel only of the full range audio is then sent to both the

left and right channels of the stereo headphone out.

REGISTERS

The LM4931 starts on power-up with all registers cleared in

Powerdown mode. Powerdown mode is the recommended

time to make setup changes to the digital interfaces (PCM

bus, I

2S bus). Although the configuration registers can be

changed in any mode, changes made during Standby or

Powerdown prevent unwanted audio artifacts that may occur

during rapid mode changes with the outputs active. The

LM4931 also features a soft reset. This reset is enabled by

setting bit 4 of the BASIC_CONFIG (00h) register. DAC

dither may also be controlled in this register (bit 5).

The VOICE_CONFIG (01h) register is used to set various

configuration parameters on the voiceband and full-range

audio codecs. SIDETONE_ATTEN (bits 3:0) refers to the

level of signal from the MIC input that is fed back into the

analog audio output path (commonly used in headphone

applications and killed in hands-free applications). Setting

the AUTOSIDE bit (bit 4) automatically mutes the sidetone in

voice over mono speaker modes so feedback isn’t an issue.

Dither for the voice ADC and DAC may be disabled by

setting bits 6 or 7, respectively. Bit 5 is reserved.

The MIC_GAIN (02h) register provides for microphone

preamplifier gains of 6dB to 36dB in 2dB steps (bits 3:0). A

quick mute bit is provided for the mic (bit 4) as well as a bit

to disable the high-pass filter on the voice ADC, allowing

wider bandwidth usage through the microphone input.

The HP_GAIN (03h) register provides settings for head-

phone control. Bits 4:0 set the gain of the headphone output

from –46.5dB to 0dB in 1.5dB steps. A quick mute bit is also

provided (bit 5). Additionally, the LM4931 may be configured

to react to a high or low HP_SENSE voltage (bit 6) and may

also provide this output on the GPIO pin in either positive or

negative form (bit 7). This will only be seen on the GPIO

output if it is configured to show HP_CONNECTED as de-

scribed in the GPIO section.

The LS_GAIN (04h) register is used to set the mono class D

loudspeaker gain. Bits 4:0 set this from –34.5dB to +12dB in

1.5dB steps. A quick mute (bit 5) is provided as well as an

auto-mute bit (bit 6) that, if set, automatically mutes the

loudspeaker when headphone sense detects that head-

phones have been connected. A powerdown bit (bit 7) is also

provided to independently shutdown just the class D ampli-

fier.

CLK_MUX (08h) is the clock divider register. Bit 0 sets the

PLL input source. When clear, MCLK is used, when set, the

2S input clock is used. Bit 1 gives a divide by 2 for usage

with a faster MCLK (like 24.576MHz). Bit 2 selects which

clock is passed to the full range audio subsystem. If clear,

the PLL output is used. If set, MCLK (or MCLK/2 if set) is

used directly. Bit 3 does the same for the voice codec

subsystem. If clear, the PLL output is used. If set, MCLK or

MCLK/2 is used. Bit 4 powers down the PLL (if not needed).

Bits 6:5 program the Q divider, that can be further used to

divide down the PLL output frequency. Bit 7 is reserved.

The INTERFACES (09h) register controls all the digital in-

terface configurations. This may be used to set the PCM

configuration and I

2S configuration as stated above in the

PCM Bus Interface and I

2S Bus Interface sections. Bits 6 is

reserved for test modes.

The PMC_CONFIG (0Ah) register controls various power

management responsibilities including bypass capacitor size

(bits 2:1). Zero crossing disable (bit 0) is also provided to

allow the LM4931 to change modes regardless of zero

crossing detect status. If set, the LM4931 will change modes

immediately without waiting for the outputs to cross zero.

Bits 6 is reserved.

PLL Registers

The PLL will accept incoming clock frequencies from 10MHz

to 25MHz. However, since the control clocks, PCM clocks,

and I

2S clocks all operate at fixed, defined frequencies the

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