LM4546B datasheet(15/27 Pages) NSC

15 / 27 page

Functional Description

GENERAL

The LM4546B codec can mix, process and convert among

analog (stereo and mono) and digital (AC Link format) inputs

and outputs. There are two stereo and four mono analog

inputs and one stereo and one mono analog outputs. A

single codec supports data streaming on two input and two

output channels of the AC Link digital interface simulta-

neously.

ADC INPUTS AND OUTPUTS

Both stereo analog inputs and three of the mono analog

inputs can be selected for conversion by the 18-bit stereo

ADC. Digital output from the left and right channel ADCs is

always located in AC Link Input Frame slots 3 and 4 respec-

tively. Input level to either ADC channel can be muted or

adjusted from the Record Gain register, 1Ch. Adjustments

are in 1.5 dB steps over a gain range of 0 dB to +22.5 dB and

both channels mute together (D15). Input selection for the

ADC is through the Record Select Mux controlled from the

Record Select register, 1Ah, together with microphone se-

lection controlled by the MS bit (D8) in the General Purpose

differential 3-pin interface where both stereo channel inputs

are referenced to the third pin, CD_GND. CD_GND should

be AC coupled to the source ground and provides common-

mode feedback to cancel ground noise. It is not a DC

ground. The other stereo input, LINE_IN, is a 2-pin interface,

single-ended for each stereo channel with analog ground

(AV

SS) as the signals’ reference. Either of the two mono

microphone inputs can be muxed to a programmable boost

amplifier before selection for either channel of the ADC. The

Microphone Mux is controlled by the Microphone Selection

(MS) bit (D8) in the General Purpose register 20h and the 20

dB programmable boost is enabled by the 20dB bit (D6) in

rectly to the Record Select Mux, is PHONE.

ANALOG MIXING: MIX1

Three analog inputs are available for mixing at the stereo

mixer, MIX1 – both stereo and one mono, namely the micro-

phone input selected by MS (D8, reg 20h). Digital input to the

codec can be directed to either MIX1 or to MIX2 after con-

version by the 18-bit stereo DAC and level adjustment by the

PCM Out Volume control register (18h). Each input to MIX1

may be muted or level adjusted using the appropriate Mixer

Input Volume Register: Mic Volume (0Eh), Line_In Volume

(10h), CD Volume (12h) and PCM Out Volume (18h). The

mono microphone input is mixed equally into left and right

stereo channels but stereo mixing is orthogonal, i.e. left

channels are only mixed with other left channels and right

with right. The left and right amplitudes of any stereo input

may be adjusted independently however mute for a stereo

input acts on both left and right channels.

DAC MIXING AND 3D PROCESSING

Control of routing the DAC output to MIX1 or MIX2 is by the

POP bit (D15) in the General Purpose register, 20h. If MIX1

is selected (default, POP=0) then the DAC output is avail-

able for processing by the National 3D Sound circuitry. If

MIX2 is selected, the DAC output will bypass the 3D pro-

cessing. This allows analog inputs to be enhanced by the

analog 3D Sound circuitry prior to mixing with digital audio.

The digital audio may then use alternative digital 3D en-

hancements. National 3D Sound circuitry is enabled by the

3D bit (D13) in the General Purpose register, 20h, and is a

fixed depth implementation. The 3D Control register, 22h, is

therefore not programmable (read-only). The 3D Sound cir-

cuitry defaults to disabled after reset.

ANALOG MIXING: MIX2

MIX2 combines the output of MIX1 (Stereo Mix 3D) with the

two mono analog inputs, PHONE and PC_BEEP; each are

each level-adjusted by the input control registers, Phone

Volume (0Ch) and PC_Beep Volume (0Ah), respectively. If

selected by the POP bit (D15, reg 20h), the DAC output is

also summed into MIX2.

STEREO MIX

The output of MIX2 is the signal, Stereo Mix. Stereo Mix is

used to drive the Line output (LINE_OUT) and can also be

selected as the input to the ADC by the Record Select Mux.

In addition, the two channels of Stereo Mix are summed to

form a mono signal (Mono Mix) also selectable by the

Record Select Mux as an input to either channel of the ADC.

STEREO OUTPUT

The output volume from LINE_OUT can be muted or ad-

justed by 0 dB to 45 dB in nominal 3 dB steps under the

control of the Master Volume register, 02h. As with the input

volume registers, adjustments to the levels of the two stereo

channels can be made independently but both left and right

channels share a mute bit (D15).

MONO OUTPUT

The mono output (MONO_OUT) is driven by one of two

signals selected by the MIX bit (D9) in the General Purpose

mono summation of the two channels of Stereo Mix 3D, the

stereo output of the mixer MIX1. Setting the control bit MIX =

1, selects a microphone input, MIC1 or MIC2. The choice of

microphone is controlled by the Microphone Select (MS) bit

(D8) also in the General Purpose register, 20h.

ANALOG LOOPTHROUGH AND DIGITAL LOOPBACK

Analog Loopthrough refers to an all-analog signal path from

an analog input through the mixers to an analog output.

Digital Loopback refers to a mixed-mode analog and digital

signal path from an analog input through the ADC, looped-

back (LPBK bit – D7, 20h) through the DAC and mixers to an

analog output. This is an 18 bit digital loopback, bypassing

the SRC logic, at a 48 kHz rate, even if another sample rate

conversion is selected.

RESETS

COLD RESET is performed when RESET# (pin 11) is pulled

low for > 1 µs. It is a complete reset. All registers and

internal circuits are reset to their default state. It is the only

reset which clears the ATE and Vendor Test Modes.

WARM RESET is performed when SYNC (pin 10) is held

high for > 1 µs and the codec AC Link digital interface is in

powerdown (PR4 = 1, Powerdown Control / Status register,

26h). It is used to clear PR4 and power up the AC Link digital

interface but otherwise does not change the contents of any

registers nor reset any internal circuitry.

to the RESET register, 00h. It resets all registers to their

default state and will modify circuit configurations accord-

ingly but does not reset any other internal circuits.

LM4546B Datasheet(PDF) 15 Page - National Semiconductor (TI)

LM4546B Datasheet(HTML) 15 Page - National Semiconductor (TI)

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Datasheet Download

Link URL