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Endpoints

Internal Regulator

Clock and Reset

DAC

ADC

Microphone Bias

PCM2912

SLES216 – FEBRUARY 2008

The PCM2912 has three endpoints as follows.

• Control endpoint (EP #0)

• Isochronous-out audio data stream endpoint (EP #1)

• Isochronous-in audio data stream endpoint (EP #2)

The control endpoint is a default endpoint. The control endpoint is used to control all functions of the PCM2912

by the standard USB request and USB audio-class-specific request from the host. Isochronous-out audio data

stream endpoint is an audio sink endpoint, which receives the PCM audio data. The isochronous-out audio data

stream endpoint accepts the adaptive transfer mode. Isochronous-in audio data stream endpoint is an audio

source endpoint, which transmits the PCM audio data. The isochronous-in audio data stream endpoint uses

synchronous transfer mode.

All required power sources are generated by five internal regulators.

ground return pin as follows, and this pair must be decoupled with an appropriate capacitor. Note that this

capacitance affects inrush-current limitation. One band-gap reference circuit supplies reference voltage for all

regulators. BGND (pin 1) is provided for reference ground of the band-gap reference.

SUPPLIED CIRCUIT

OUTPUT

RETURN

Digital

DGND (pin 6)

Analog

AGND (pin 13)

Headphone (L-ch)

HGND (pin 20)

Headphone (R-ch)

HGND (pin 20)

PLL

PGND (pin 25)

The PCM2912 requires a 6-MHz (±500 ppm) clock for USB function and audio function, which can be generated

by a built-in crystal oscillator with a 6-MHz crystal resonator. The 6-MHz crystal resonator must be connected to

XTI (pin 8) and XTO (pin 7) with one high (1-M

Ω) resistor and two small capacitors, whose capacitance depends

on the load capacitance of the crystal resonator. An external clock can be supplied from XTI; if an external clock

is supplied, XTO must be left open. Because there is no clock disabling signal, using the external clock supply is

not recommended. SSPND (pin 29) is unable to use clock disabling.

V, typical (2.2 V–2.7 V), and approximately 700

µs is required until the internal reset is released.

(pin 22) can provides 13 mW at 32

PGA which has +30 dB to –12 dB in 1-dB steps.

output with appropriate output impedance for electret-microphone driving. This output, MBIAS (pin 17) should be

bypassed to AGND (pin 13) through an appropriate capacitor for reducing output noise level.

Copyright © 2008, Texas Instruments Incorporated

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Product Folder Link(s): PCM2912