LM49352 datasheet(48/106 Pages) TI

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LM49352

SNAS467E – MARCH 2009 – REVISED MARCH 2013

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Table 28. DAC Basic (0x30h) (continued)

Bits

Field

Description

6:4

DAC_CLK_SEL

This selects the source of the DAC clock domain, DAC_SOURCE_CLK.

DAC_CLK_SEL

Source

000

MCLK

001

PORT1_RX_CLK

010

PORT2_RX_CLK

011

PLL_OUTPUT1

100

PLL_OUTPUT2

DSP_ONLY

If set, the DAC's analog circuitry is disabled to reduce power consumption, however DAC DSP

functionality is maintained. This can be used to perform asyncronous resampling between audio rates of

a common family.

Table 29. DAC_CLK_DIV (0x31h)

Bits

Field

Description

7:0

DAC_CLK_DIV

This programs the half cycle divider that precedes the DAC. The input of this divider should be around

12MHz. The default of this divider is 0x03 which gives a division by 2.

Program this divider with the division you want, multiplied by 2, and subtract 1.

DAC_CLK_DIV

Divides by

00000000

00000001

00000010

1.5

00000011

2 (Default)

—

11111101

127

11111110

127.5

11111111

128

Digital Mixer Control Registers

Digital Mixer

The LM49352’s digital mixer allows for flexible routing of digital audio signals between both audio ports, DAC,

and ADC. This mixer handles which digital data path (Port1 RX data, Port2 RX data, or ADC output) is routed to

the DAC input. The digital mixer also selects the appropriate digital data path (Port1 RX data, Port2 RX data,

ADC output, or DAC DSP (Interpolator) output) that is used for data transmission on Audio Port 1 and 2. Audio

inputs to the digital mixer can be attenuated down to -18dB to avoid clipping conditions. The digital mixer also

allows direct routing from the DAC interpolator output to the ADC decimator input which allows the DAC and

ADC DSP blocks to be cascaded witjhout having to enable the analog of the DAC and ADC in order to save

power.

Another key feature of the digital mixer is sample rate conversion (SRC) between audio ports. This allows

simultaneous operation of the dual audio ports even if each port is operating at a different sample rate. The

LM49352 can be used as an audio port bridge with SRC capability. The digital mixer allows either straight pass

through between audio ports or, if desired, DSP effects can be added to the digital audio signal during audio port

bridge operation. The digital mixer automatically handles stereo I2S to mono PCM conversion between audio

ports and vice versa.

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