PCM5121 datasheet(42/121 Pages) TI2

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OUTL

OUTR

470Ω

2.2nF

LINE

OUT

470Ω

2. 2nF

Output voltage is 2 VRMS

With a 10 kΩ Load

PCM5121, PCM5122

SLAS763C – AUGUST 2012 – REVISED OCTOBER 2018

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Product Folder Links: PCM5121 PCM5122

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8.3.5 DAC Outputs

8.3.5.1 Analog Outputs

The PCM512x devices include a two-channel DAC, with single-ended outputs. The full-scale output voltage is

2.1Vrms with ground center output. A dc-coupled load is supported in addition to an ac-coupled load, if the load

resistance conforms to the specification. The PCM512x DAC outputs on the OUTL and OUTR terminals have

market-leading low out-of-band noise, which offer up to 20dB lower out-of-band noise compared with existing

DAC technology.

Most applications require an external low-pass RC filter (470Ω + 2.2nF) to provide sufficient out-of-band noise

rejection. This RC filter provides the added advantage of improved protection against ESD damage.

8.3.5.2 Recommended Output Filter for the PCM512x

The diagram in Figure 61 shows the recommended output filter for the PCM512x. The new PCM512x next-

generation current segment architecture offers excellent out-of-band noise, making a traditional 20-kHz low pass

filter a thing of the past.

The RC settings below offer a –3-dB filter point at 153 kHz (approximately), giving the DAC the ability to

reproduce virtually all frequencies through to it’s maximum sampling rate of 384 kHz. A NP0/C0G type capacitor

is strongly recommended for the shunt capacitor for lowest distortion.

Figure 61. Recommended Output Lowpass Filter for 10-kΩ Operation

8.3.5.3 Choosing Between VREF and VCOM Modes

VREF mode is the default configuration. This mode allows full 2.1-Vrms signal output. As shown in Recommended

Operating Conditions, the minimum AVDD to avoid clipping is 3.2 V.

VCOM mode allows setting a custom common-mode voltage when required by the application. This somewhat

limits the output signal swing before clipping.

8.3.5.3.1

Voltage Reference and Output Levels

The PCM512x devices have an internal, fixed band-gap reference voltage, with default operation in VREF mode.

No external decoupling capacitor is required for this mode.

The PCM512x devices can be operated with a common-mode voltage output (VCOM mode) at the VCOM pin by

setting Page 1, Register 1, D(0) to 1. In this mode, an external decoupling capacitor is required.

When using this DAC in VREF mode, the output-signal voltage is independent of the power-supply voltage: The

D/A conversion gain in VREF mode yields a 2.1-Vrms output voltage with a digital full-scale input. However, in

VREF mode, an output waveform may clip due to the limitations that may be present in the analog power supply

voltage. On the other hand, the full-scale output voltage in VCOM mode is proportional to the analog power

supply AVDD (for example, (2.1 × AVDD / 3.3) Vrms).

PCM5121 Datasheet(PDF) 42 Page - Texas Instruments

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