NRND

TP3404

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SNOS703 – DECEMBER 2004

APPLICATIONS INFORMATION

POWER SUPPLIES

While the pins of the TP3404 QDASL device are well protected against electrical misuse, it is recommended that

the standard CMOS practice of applying GND to the device before any other connections are made should

always be followed. In applications where the printed circuit card may be plugged into a hot socket with power

and clocks already present, an extra long ground pin on the connector should be used.

To minimize noise sources, the VDDA and VDDD pins should be connected together via the shortest possible

trace; likewise the GNDA and GNDD pins must be connected together. These two connections can be done

directly underneath the part. All other ground connections to each device should meet at a common point as

close as possible to the GNDD pin in order to prevent the interaction of ground return currents flowing through a

common bus impedance. A power supply decoupling capacitor of 0.1

μF should be connected from this common

point to VDDD as close as possible to the device pins.

Figure 6 shows a typical 4 line application of the QDASL. The current list of suitable commercial transformers is:

Schott Corporation (Nashville);

Phone 615-889-8800.

Part numbers: 67110850 (dry);

Pulse Engineering (San Diego);

Phone 619-674-8100.

Part number:TBD.

Note that the Zener diode protection shown in Figure 9 is only intended as secondary protection for inside wiring

applications; primary protection is also necessary. Further information can be found in the datasheet for the

TP3401/2/3 DASL devices (SNOSC12) and in Application Note AN-509 “Using the TP3401/2/3 ISDN PBX

Transceivers”.

Copyright © 2004, Texas Instruments Incorporated

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