ANALOG OUTPUTS

VCOM OUTPUT

–

VOUTX

PCM1680

A

V + *

R

2

R

1

VCOM

OPA2134

+

VCC

2

3

1

C1

R3

R2

C2

R1

C3

10

µF

+

S0056-01

R4

R5

+

OPA337

−

To Additional

Low-Pass

Filter Circuits

PCM1680

SLES133B – MARCH 2005 – REVISED OCTOBER 2008.................................................................................................................................................. www.ti.com

The PCM1680 includes eight independent output channels, VOUT1 through VOUT8. These channels are

unbalanced outputs, each capable of driving 3.9 VPP typical into a 5-kΩ ac load with VCC = 5 V. The internal

output amplifiers for VOUT1 through VOUT8 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 PCM1680

ΔΣ DACs. The frequency

response of this filter is shown in Figure 11. By itself, this filter is not enough to attenuate the out-of-band noise

to an acceptable level for most 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 25), is brought out for decoupling purposes. This pin is

nominally biased to the dc common voltage, equal to VCC/2. If this pin is to be used to bias external circuitry, a

voltage follower is required for buffering purposes. Figure 31 shows an example of using the VCOM pin for

external biasing applications.

Figure 31. Single-Supply Filter Circuit Using VCOM for External Biasing Applications

28

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