PCM4104IPFBREP datasheet(15/43 Pages) TI

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VOLTAGE REFERENCES

(1) Capacitor(s) required for each of the four reference pairs.

REF+

(1)

COM1

0.01

µF

0.1

µF

0.1

µF

0.1

µF to 10µF

COM2

REF−

(1)

SAMPLING MODES

PCM4104-EP

SBAS419 – JUNE 2007

PRODUCT OVERVIEW (continued)

The PCM4104 includes high and low reference pins for each output channel. VREF1+ (pin 5) and VREF1– (pin 4)

correspond to Channel 1. VREF2+ (pin 44) and VREF2– (pin 43) correspond to Channel 2. VREF3+ (pin 41) and

VREF3– (pin 42) correspond to Channel 3. VREF4+ (pin 32) and VREF4– (pin 33) correspond to Channel 4.

The high reference (+) pin may be connected to the corresponding VCC supply or an external 5-V reference,

while the low reference (–) pin is connected to analog ground. A 0.01-

μF bypass capacitor should be placed

between the corresponding high and low reference pins. An X7R ceramic chip capacitor is recommended for this

purpose. In some cases, a larger capacitor may need to be placed in parallel with the 0.01-

μF capacitor, with the

value of the larger capacitor being dependent upon the low-frequency power-supply noise present in the system.

Typical values may range from 1

μF to 10 μF. Low ESR tantalum or multilayer ceramic chip capacitors are

recommended. Figure 3 illustrates the recommended connections for the reference pins.

Figure 3. Recommended Connections for Voltage Reference and Common-Mode Output Pins

In addition to the reference pins, there are two common-mode voltage output pins, VCOM1 (pin 48) and VCOM2

(pin 37). These pins are nominally set to a value equal to VCC/2 by internal voltage dividers. The VCOM1 pin is

common to both Channels 1 and 2, while the VCOM2 pin is common to Channels 3 and 4. A 0.1-μF X7R ceramic

chip capacitor should be connected between the common-mode output pin and analog ground. The

common-mode outputs are used primarily to bias external output circuitry.

The PCM4104 can operate in one of three sampling modes: Single Rate, Dual Rate, or Quad Rate. Sampling

modes are selected by using the FS[1:0] bits in Control Register 6 in Software mode, or by using the FS0 (pin

28) and FS1 (pin 29) inputs in Standalone mode.

The Single Rate mode allows sampling frequencies up to and including 54 kHz. The D/A converter performs

128

× oversampling of the input data in Single Rate mode.

The Dual Rate mode allows sampling frequencies greater than 54 kHz, up to and including 108 kHz. The D/A

converter performs 64

× oversampling of the input data in Dual Rate mode.

The Quad Rate mode allows sampling frequencies greater than 108 kHz, up to and including 216 kHz. The D/A

converter performs 32

× oversampling of the input data in Quad Rate mode.

Refer to Table 1 for examples of system clock requirements for common sampling frequencies.

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