PCM2702

8

SBAS142A

www.ti.com

THEORY OF OPERATION

USB INTERFACE

The description of the USB interface complies with Univer-

sal Serial Bus specification Rev. 1.0.

Control and audio data are both transferred to the PCM2702

via D+ (pin 6) and D– (pin 7). All data to/from the PCM2702

consumes USB bus power, it is used only for detecting the

connection of the USB bus. The following information is

provided in the device descriptor.

The Input Terminal is defined as “USB stream” (terminal

type 0x0101). The Input Terminal can accept 2-channel

audio streams comprised of left and right channel data. The

Output Terminal is defined as a “speaker” (terminal type

0x0301). The Feature Unit supports the following sound

control features.

• Volume Control

• Mute Control

The built-in digital volume controller can be manipulated by

an audio class specific request from 0.0dB to –64.0dB in

steps of 1.0dB. Each channel can be set independently. The

master volume control is also supported. The built-in digital

mute controller can be manipulated by an audio class spe-

cific request. A master mute-control request is acceptable. A

request to an individual channel will be stalled and ignored.

Interface #1 has three alternative settings. Alternative setting

#0 is the Zero Bandwidth setting. Alternative setting #1 is

the 16-Bit Stereo setting, and is an operational setting.

Alternative setting #2 is the 16-Bit Monaural setting, and is

also an operational setting. The PCM2702 has the following

two endpoints.

• Control Endpoint (EP #0)

• Isochronous Audio Data Stream Endpoint (EP #2)

The Control Endpoint is a default endpoint and is used to

control all functions of the PCM2702 by the standard USB

request and the USB audio class specific request. The

Isochronous Audio Data Stream Endpoint is an audio sink

endpoint, which receives the PCM audio data, and accepts

the adaptive transfer mode.

USB Revision

1.0

Device Class

0x00 (device defined interface level)

Device Subclass

0x00 (not specified)

Device Protocol

0x00 (not specified)

Max Packet Size for Endpoint 0

8 byte

Vendor ID

0x08BB

Device ID

0x2702

Release

1.0

TABLE I. Device Definition.

DEVICE CONFIGURATION

Figure 1 illustrates USB audio function topology. The

PCM2702 has two interfaces. Each interface is constructed

by some alternative setting. Interface #0 has one alternative

setting. Alternative setting #0 describes the standard audio

control interface. The audio control interface is constructed

by a terminal. The PCM2702 has the following three termi-

nals.

• Input Terminal (IT)

• Output Terminal (OT)

• Feature Unit (FU)

Endpoint #0

PCM2702

Default

Endpoint

Endpoint #2

Audio Streaming Interface

(IF #1)

IT

TID1

OT

TID2

Standard Audio Control Interface (IF #0)

FU

UID3

Analog Out

NOTE: IT = Input Terminal (Terminal ID #1); OT = Output Terminal (Terminal ID #2); FU = Feature Unit (Unit ID #3).

FI