T7264 データシートの表示（PDF） - Agere -> LSI Corporation

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T7264

U-Interface 2B1Q Transceiver

Agere -> LSI Corporation 

Data Sheet

April 1998

T7264 U-Interface 2B1Q Transceiver

Functional Overview (continued)

Device Interface and Connections

The device provides rapid cold start and warm start op-

eration. From a cold start, the device is typically opera-

tional within 3.5 s. The device supports activation/

deactivation, and, when properly deactivated, it stores

the adaptive filter coefficients such that upon the next

activation request, a faster warm start is possible. A

warm start typically requires 200 ms for the device to be-

come operational.

The T7264 has an on-chip activation/deactivation state

machine and timers, and automatically moves from

state T0 to T7 (as specified in the T1.601 standard) dur-

ing activation. This simplifies the implementation of the

T1.601 (Appendix C) state table. The signals from the

device control and status octets on the K2 interface pro-

vide the control necessary to complete the state table.

The activation/deactivation process is controlled over

the K2 interface.

The T7264 has a low-power mode which it automatically

enters when it is in the idle state. The idle state occurs

after deactivation, loss of sync on the U-interface, or re-

leasing reset. In the low-power mode, power consump-

tion is typically 30 mW.

The T7264 transceiver allows systems to meet the

loop-range requirements of ANSI Standard T1.601

when the transceiver is used with the proper peripheral

circuitry. Devices achieve better than 10–7 bit error rate

over 18 kft of 26 AWG loop cable.

Analog Device Interface

Proper line termination is required, utilizing appropriate

interface components, to meet the 2.5 V pulse tem-

plate. The output of the T7264 should first pass through

a pair of 16.9 Ω resistors and into a 1.5:1 ratio trans-

former, such as the Lucent 2754H (or the short-lead

version 2754H2). The output of the transformer is cou-

pled through a 1.0 µF capacitor, is passed through a

pair of 16.9 Ω resistors, and then drives the 135 Ω line.

Surge protection circuitry is necessary on each side of

the transformer when the U loop is external to a build-

ing. The protection between the 16.9 Ω resistors and

the transformer should be a Lucent 521A surge protec-

tor or equivalent. A relay may be needed to disconnect

the loop plant for local loopback testing. Figure 4 shows

a recommended circuit for interfacing the T7264 to the

line; however, the specific interface is system depen-

dent.

820 pF ± 5%

16.9 Ω ± 7%

SURGE

PROTECTION

16.9 Ω ± 7%

LOOPBACK

RELAY

2754H

1.5:1

7

1

10

6

9

5

16.9 Ω ± 1%

521A

SURGE

PROTECTION

16.9 Ω ± 1%

1.0 µF

LUCENT

701C

dc

REMOTE

POWER

SOURCE

36 HP

32 LOP

37

38

T7264

35 LON

31 HN

29 28 30 24

0.1 µF

GNDA

5-5803Fa

Note: 3000 pF ± 1% capacitors from HP and HN to GNDA may improve operation of the tone decoder in the presence of interfering common-

mode signals.

Figure 4. Line Interface and Protection

Lucent Technologies Inc.

7

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