PCM1741ESLASH2K datasheet(15/24 Pages) TI2

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PCM1741

SBAS175

ANALOG OUTPUTS

The PCM1741 includes two independent output channels:

VOUTL and VOUTR. These are unbalanced outputs, each capable

of driving 2.05Vp-p typical into a 5k

Ω AC-coupled load. The

internal output amplifiers for VOUTL and VOUTR are biased to the

DC common-mode (or bipolar zero) voltage, equal to VCC/2.

The output amplifiers include an RC continuous-time filter that

helps to reduce the out-of-band noise energy present at the

DAC outputs, due to the noise shaping characteristics of the

PCM1741’s delta-sigma DACs. The frequency response of this

filter is shown in Figure 8. By itself, this filter is not enough to

attenuate the out-of-band noise to an acceptable level for many

applications, therefore, an external low-pass filter is required to

provide sufficient out-of-band noise rejection. Further discus-

sion of DAC post-filter circuits is provided in the Applications

Information section of this data sheet.

VCOM OUTPUT

One unbuffered common-mode voltage output pin, VCOM

(pin 10), is brought out for decoupling purposes. This pin is

FIGURE 8. Output Filter Frequency Response.

0.1

100

10K

–10

–20

–30

–40

–50

–60

Frequency (kHz)

ANALOG FILTER PERFORMANCE

(100Hz-10MHz)

nominally biased to a DC voltage level equal to VCC/2. This

pin may be used to bias external circuits. Figure 9 shows an

example of using the VCOM pin for external biasing applica-

tions.

FIGURE 9. Biasing External Circuits Using the VCOM Pin.

µF

(a) Using V

COM to Bias a Single-Supply Filter Stage

(b) Using a Voltage Follower to Buffer V

COM when Biasing Multiple Nodes

x = L or R

µF

Filtered

Output

OPA342

V = –1, where AV = –

OUTx

COM

PCM1741

Buffered

COM

1/2

OPA2342

µF

PCM1741

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