PCM1780 datasheet(25/31 Pages) TI

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ANALOG OUTPUTS

VCOM Output

–

VCOM

OPA337

µF

PCM1780/81/82

Buffered VCOM

VCC

VOUTX†

PCM1780/81/82

V + *1, where AV + *

VCOM

† X = L or R

1/2

OPA2353

VCC

µF

(a) Using VCOM to Bias a Single-Supply Filter Stage

(b) Using a Voltage Follower to Buffer VCOM When Biasing Multiple Nodes

S0054-01

PCM1780, PCM1781, PCM1782

SLES132A – MARCH 2005 – REVISED APRIL 2005

The PCM1780/81/82 includes two independent output channels, VOUTL and VOUTR. These are unbalanced

outputs, each capable of driving 3.9 Vp-p typical into a 5-k

Ω ac-coupled load. The internal output amplifiers for

VOUTL and VOUTR are biased to the dc common voltage, equal to 0.5 VCC.

The output amplifiers include an RC continuous-time filter, which helps to reduce the out-of-band noise energy

present at the DAC outputs due to the noise-shaping characteristics of the PCM1780/81/82 delta-sigma D/A

converters. The frequency response of this filter is shown as ANALOG FILTER in the Typical Performance

Curves section. By itself, this filter is not enough to attenuate the out-of-band noise to an acceptable level for

many applications. An external low-pass filter is required to provide sufficient out-of-band noise rejection. Further

discussion of DAC post-filter circuits is provided in the Application Information section of this data sheet.

One unbuffered common voltage output pin, VCOM (pin 13), is brought out for decoupling purposes. This pin is

nominally biased to the dc common voltage, equal to VCC/2. This pin can be used to bias external circuits.

Figure 27 shows an example of using the VCOM pin for external biasing applications.

Figure 27. Biasing External Circuits Using the VCOM Pin

PCM1780 Datasheet(PDF) 25 Page - Texas Instruments