ADAU1373BCBZ-R7 datasheet(41/296 Pages) AD

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ADAU1373

Rev. 0 | Page 41 of 296

Input Impedance

The input resistance for Analog Input 1 through Analog Input 4

(AINx, Ball A5 through Ball A8 and Ball B5 through Ball B8)

depends on the gain mode setting. The input resistance is lowest

(at approximately 5.6 kΩ) for a +18 dB gain in PGA mode, and

it is highest (at approximately 47 kΩ) for a −12 dB setting. In

boost mode, the input resistance is constant at 20 kΩ. The input

resistance must be considered when calculating the required input

coupling capacitor. It is recommended that the lowest value of

the impedance be used when determining the microphone input

coupling capacitor.

Common-Mode Input Voltage

The common-mode voltage at the input pins (AINx) is typically

at AVDD/2. The common-mode voltage at the inputs is turned

off when the inputs are muted. The common-mode voltage

rises slowly as the inputs are unmuted and charges the input

capacitors. To prevent the turn on pop, it is recommended that

the inputs be unmuted in the ADAU1373 and be muted at the

source. If this recommendation is not adhered to, there is a

possibility of a turn on pop as the common-mode voltage at the

inputs charges up.

MIXER BLOCK

The ADAU1373 provides the analog mixer block for mixing the

analog inputs. The mixer block is available prior to the ADC,

line output, headphone output, speaker output, and earpiece

output, which provides the system designer with many

configuration options.

ADC Mixer Input

The mixer prior to the ADC input allows selection of any or all of

the four analog inputs. When multiple inputs are selected, they are

mixed prior to the ADC. Register 0x12 and Register 0x13 can be

used to select the signals that are input to the ADC mixer.

Line Mixer Output

The mixer prior to the line output amplifier allows selection of any

or all of the four analog inputs, as well as the DAC outputs. When

multiple inputs are selected, they are mixed prior to the line

output amplifier. Register 0x14 through Register 0x17 can be

used to select the signals that are input to the line mixer.

Headphone Mixer Output

The mixer prior to the headphone output amplifier allows

selection of any or all of the four analog inputs, as well as the

DAC outputs. When multiple inputs are selected, they are mixed

prior to the headphone output amplifier. Register 0x1A and

headphone mixer.

Speaker Mixer Output

The mixer prior to the headphone output amplifier allows selection

of any or all of the four analog inputs, as well as the DAC outputs.

going to the speaker mixer.

Earpiece Mixer Output

The mixer prior to the earpiece amplifier allows selection of

any or all of the four analog inputs, as well as the DAC output.

When multiple inputs are selected, they are mixed prior to the

earpiece output amplifier. Register 0x1C can be used to select

the signals going to the earpiece mixer.

ANALOG OUTPUTS

Line Output

The ADAU1373 provides two single-ended stereo line level outputs

on LOUT1L (Ball C7) and LOUT1R (Ball D7) or on LOUT2L

(Ball D8) and LOUT2R (Ball D9). The line level outputs can be

configured as single-ended or differential. The stereo differential

outputs are available on LOUTLP (Ball C7) and LOUTLN

(Ball D8) or on LOUTRP (Ball D7) and LOUTRN (Ball D9). The

line output control register (Register 0x24) can be used to set the

line output mode. The outputs have series resistance to protect

against output short circuit. The typical recommended load

impedance is approximately 47 kΩ. The line output amplifier uses

AVDD as its supply; therefore, the common-mode output level

on the line output pins is AVDD/2. Coupling capacitors must be

used before connecting the outputs to the desired load. The value

of the capacitors can be determined by the following:

Frequency f (3 dB) = 1/(2 × π × ROUT × COUT)

where ROUT = 0.3 Ω.

Set the desired 3 dB low frequency at the output. The line outputs

can receive input from any or all of the four inputs directly or

from the DAC (see Figure 87 and Figure 88 for block diagrams).

The line outputs have a ground noise rejection feature that can be

enabled using Register 0x24, Bit 2 (LNFBEN). When enabled, the

line output amplifier rejects the noise on LN1FBIN (Ball E7) and

LN2FBIN (Ball E8). To use this feature, E7 and E8 must be con-

nected directly to the ground node (typically, the sleeve contact

of the line output socket) using a capacitor. The ground noise

rejection feature is very useful in applications where the line

outputs are used to connect to an external audio system (such as

a home theater or docking station) that works on a different power

supply and can cause a ground loop when connected to the line

output using a single-ended (unbalanced) connection.

Line Output Full-Scale Level

The full-scale output for the line output depends on AVDD.

At AVDD = 1.8 V, the full-scale output level is 0.5 V rms single-

ended or 1 V rms differential. The full-scale input level scales

linearly with the level of AVDD.

Line Output Volume Control

The line output level can be controlled using Register 0x09

(Left Channel Line Output 1 volume control), Register 0x0A

(Right Channel Line Output 1 volume control), Register 0x0B

(Left Channel Line Output 2 volume control), and Register 0x0C

(Right Channel Line Output 2 volume). The volume control

range is from mute to 0 dB in 32 steps.

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