PCM1608 datasheet(22/29 Pages) TI

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PCM1608

SBAS164A

B15

B14

B13

B12

B11

B10

R/W

IDX6

IDX5

IDX4

IDX3

IDX2

IDX1

IDX0

RSV

DAC8

DAC7

R/W

Read/Write Mode Select

When R/W = 0, a write operation is performed.

When R/W = 1, a read operation is performed.

Default Value: 0

DACx

DAC Operation Control

Where x = 7-8, corresponding to the DAC output VOUTx.

These bits are Read/Write.

Default Value: 0

DACx = 0

DAC Operation Disabled (default)

DACx = 1

DAC Operation Enabled

The DAC operation controls are used to enable and disable the DAC outputs, VOUT7 and VOUT8. When

DACx = 0, the output amplifier input is connected to the DAC output. When DACx = 1, the output amplifier

input is switched to the DC common-mode voltage (VCOM), equal to VCC/2.

ANALOG OUTPUTS

The PCM1608 includes eight independent output channels,

VOUT1 through VOUT8. These are unbalanced outputs, each

capable of driving 3.1Vp-p typical into a 5k

Ω AC load with

VCC = +5V. The internal output amplifiers for VOUT1 through

VOUT8 are DC biased to the common-mode (or bipolar zero)

voltage, equal to VCC/2.

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 PCM1608’s delta-sigma DACs. The frequency re-

sponse of this filter is shown in Figure 10. 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 Applications Information section of this data

sheet.

VCOM OUTPUT

One unbuffered, common-mode voltage output pin, VCOM

(pin 15), is brought out for decoupling purposes. This pin is

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

this pin is to be used to bias external circuitry, a voltage

follower is required for buffering purposes. Figure 11 shows

an example of using the VCOM pin for external biasing

applications.

FIGURE 10. Output Filter Frequency Response.

100

10k

100k

10M

–20

–40

–60

–80

–100

Log Frequency (Hz)

FIGURE 11. Biasing External Circuits Using the VCOM Pin.

OPA337

µF

COM

PCM1608

BIAS ≈

PCM1608 Datasheet(PDF) 22 Page - Texas Instruments

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