TLV320AIC21 datasheet(23/56 Pages) TI1

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Analog/Digital Loopback

Analog Sidetone

Digital Sidetone

Analog Input/Output

Analog Crosspoint

Analog Input Amplifier

Microphone Bias

Output Drivers

Speaker Driver

TLV320AIC20, TLV320AIC21

TLV320AIC24, TLV320AIC25

TLV320AIC20K, TLV320AIC24K

SLAS363D – MARCH 2002 – REVISED APRIL 2005

Functional Description (continued)

The analog and digital loopbacks provide a means of testing the data ADC/DAC channels and can be used for

in-circuit system level tests. The analog loopback always has the priority to route the DAC low pass filter output

into the analog input where it is then converted by the ADC to a digital word. The digital loopback routes the ADC

output to the DAC input on the device. Analog loopback is enabled by writing a 1 to bit D2 in the control register

1. Digital loopback is enabled by writing a 1 to bit D1 in control register 1.

The analog sidetone attenuates the analog input and mixes it with the output of the DAC. The control register 5C

selects the attenuation level of the analog sidetone.

The digital sidetone attenuates the ADC output and mixes it with the input of the DAC. The control register 5C

selects the attenuation level of the digital sidetone.

To produce excellent common-mode rejection of unwanted signal performance, the analog signal is processed

differentially until it is converted to digital data. The signal source driving the analog inputs should have low

source impedance for lowest noise performance and accuracy. To obtain maximum dynamic range, the signal

must be ac coupled to the input terminal. The analog output is differential from the digital-to-analog converter.

The analog crosspoint is a lossless analog switch matrix controlled via the serial control port. It allows any source

device to be connected to any sink device. Additionally, special summing connections with adjustable loss (7 × 3

dB steps) are included to implement sidetone for the headset and handset ports. (Also included is muting

function on any of the sink devices). The control of the analog crosspoint, defined in the control register 6, is to

allow any analog input or output to connect to a codec at one time. If more than one input is selected, these

inputs are mixed together before the conversion. Caution needs to be taken to make sure that both DAC

channels are not connected to the same output.

The integrated programmable gain amplifier (PGA) controls the amplification of any analog input before the

analog-to-digital converter converts the signal. The PGA's gain from 0 dB to 42 dB in 1.5-dB steps and 48 dB

and 54 dB are selected using the control register 5A.

To operate electret microphones properly, a bias voltage and current are provided. Typically, the current drawn

by the microphone is in the order of 100 µA to 800 µA and the bias voltage is specified across the microphone at

1.35 V or 2.35 V. The MICBIAS has good power supply noise rejection in the audio band and the bias voltage is

selectable, via bit D3 of control register 1, for each interface.

The HSNO and HDSO are output from two audio amplifiers to drive low-voltage speakers like those in the

handset and headset. They can drive a load of 150

Ω. The drive amplifier is differential to minimize noise and

EMC immunity problems. The frequency response is flat up to 26 kHz.

The SPKO is output from the audio amplifier that can drive an 8-

Ω speaker load. The drive amplifier is differential

to minimize noise and EMC immunity problems. The frequency response is flat up to 26 kHz.

TLV320AIC21 Datasheet(PDF) 23 Page - Texas Instruments

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