STAC9721 datasheet(46/48 Pages) ETC1

46 / 48 page

SigmaTel, Inc.

Data Sheet

STAC9721

04/07/00

Appendix B

+5.0V/+3.3V POWER SUPPLY OPERATION NOTES

The STAC9721 is capable of operating from a single 5V supply connected to both DVdd and AVdd.

Even though the STAC9721 has digital switching levels of 0.2Vdd to 0.5Vdd (See AC Link Electrical

Characteristics in this data book), we recommend that all digital interface signals to the AC-Link be 5V.

If digital interface signals below 5V are used, then appropriate level shifting circuitry must be provided to

ensure adequate digital noise immunity.

The STAC9721 can also operate from a 3.3V digital supply connected to DVdd while maintaining a 5V

analog supply on AVdd. On-chip level shifters ensure accurate logic transfers between the analog and

digital portions of the STAC9721. If digital interface signals above 3.3V are used (i.e. a +5V AC-Link

interface), then appropriate level shifting circuitry must be provided to ensure adequate digital noise

immunity and to prevent on-chip ESD protection diodes from turning on. (See Appendixes A concerning

SPLIT INDEPENDENT POWER SUPPLY OPERATION).

The STAC9723 must be run from a 3.3V supply connected to both DVdd and AVdd. If digital interface

signals above 3.3V are used (i.e. a +5V AC-Link interface), then appropriate level shifting circuitry must

be provided to ensure adequate digital noise immunity and to prevent on-ship ESD protection diodes

from turning on.

*Always operate the STAC97xx digital supply from the same supply voltage as the digital

controller supply.

*All the analog inputs must be ac-coupled with a capacitor of 0.1

µµµµF or greater. It is recommended

that a resistor of about 47K

Ω

Ω be connected from the signal side of the capacitor to analog GND as

shown below.

*All the analog outputs must be ac-coupled. If an external amplifier is used, make sure that the

input impedance of the amplifier is at least 10K

Ω

Ω and use an ac-coupling capacitor of 1.0 µµµµF.

47K

> 1.0 uF

SIGNAL

Analog Input

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