Cirrus-logic CS42L73 User Manual download pdf (Page 41)

DS882F1 41

CS42L73

4. APPLICATIONS

4.1 Overview

4.1.1 Basic Architecture

The CS42L73 is a highly integrated, ultralow power, 24-bit audio CODEC comprising a stereo ADC and

two stereo DAC converters. The ADC is fed by pseudodifferential inputs. The DACs feed two stereo pseu-

dodifferential output amplifiers and three mono (or one mono and one stereo, depending on configuration)

full-differential amplifiers. The ADC and DAC are designed using multibit delta-sigma techniques. Both

converters operate at a low oversampling ratio, maximizing power savings while maintaining high perfor-

mance.

The serial data interface ports of the CS42L73 may operate at standard audio sample rates as either the

master or slave of timing. The timing of the core of the CS42L73 is flexibly sourced, without the need of

a PLL, by clocks with typical audio clock rates (N x 5.6448 or 6.1440 MHz; N = 1 or 2), USB rates (6, 12,

or 24 MHz), or common cell phone reference rates (N x 13.0 or 19.2 MHz; N = 1 or 2).

Designed with a very low voltage digital core and low voltage Class H amplifiers (powered from an inte-

grated LDO regulator and a step-down/inverting charge pump, respectively), the CS42L73 provides sig-

nificant reduction in overall power consumption.

4.1.2 Line and Microphone Inputs

The analog input portion of the CODEC allows selection from stereo line-level or mic sources. The select-

ed source is fed into a microphone preamplifier (when applicable) and then a PGA, before entering the

stereo ADC.

When used, the pseudodifferential analog input configuration provides noise-rejection for single-ended

analog inputs to the CS42L73.

4.1.3 Line and Headphone Outputs (Class H, Ground-Centered Amplifiers)

The analog output portion of the CODEC includes separate pseudodifferential headphone and line out

Class H amplifiers. An on-chip step-down/inverting charge pump creates a positive and negative voltage

equal to the input, one-half the input, or one-third the input supply for the amplifiers, allowing an adaptable,

full-scale output swing centered around ground. The inverting architecture eliminates the need for large

DC-blocking capacitors and allows the amplifier to deliver more power to headphone loads at lower supply

voltages. The step-down architecture allows the amplifier’s power supply to adapt to the required output

signal. This adaptive power supply scheme converts traditional Class AB amplifiers into more power-effi-

cient Class H amplifiers.

4.1.4 Digital Mixer

The digital mixer facilitates the mixing and routing of the ADC and serial port audio data to the device an-

alog and Serial port outputs. All routes from inputs to outputs are supported.

All paths have selectable attenuation before being mixed to allow relative volume control and to avoid clip-

ping.

4.1.5 Power Management

Several control registers and bits provide independent power down control of the analog and digital sec-

tions of the CS42L73, allowing operation in select applications with minimal power consumption.

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Cirrus-logic CS42L73 User Manual Page 41