T7256 Agere Systems, T7256 Datasheet - Page 4

• Manufacturer Part Number: T7256
• Description: (T7234 - T7256) Compliance
• Manufacturer: Agere Systems

T7234, T7237, and T7256
Data Sheet Advisory
Application Circuit
Please change the value of capacitor C15 from 0.1 µF to 1.0 µF in Figure 11 of the T7234 data sheet, Figure 17 of
the T7237 data sheet, and Figure 20 of the T7256 data sheet. The following schematic shows the correct value
(1.0 µF) for C15.
In the ILOSS mode (refer to ANSI T1.601 1992, Section 6.5.2), the NT generates a scrambled, framed, 2B1Q sig-
nal such as SN1 and SN2. When the ILOSS mode is applied to circuits with the LH1465, it was observed that for
some short loop lengths, the NT, once in the ILOSS mode, would not respond to further maintenance pulses until
the ILOSS timer expired. It was discovered that there is some portion of the transmitted 2B1Q signal from the NT
that passes through the LH1465 to the optoisolator. This causes the optoisolator to report incorrect dial pulses at
its output, and thus prevent the NT from properly exiting the ILOSS mode.
To correct this situation, the dropout voltage (voltage at the Tip/Ring needed to turn on the optoisolator) of the
optoisolator driver on the LH1465 is raised using the 3.6 V zener diode Z
Capacitor C
a level of filtering for the transition points (turn-on or turn-off) of the optoisolator input voltage, which increases the
robustness of the circuit.
* Motorola is a registered trademark of Motorola Inc.
For additional information, contact your Microelectronics Group Account Manager or the following:
Lucent Technologies Inc. reserves the right to make changes to the product(s) or information contained herein without notice. No liability is assumed as a result of their use or application. No
rights under any patent accompany the sale of any such product(s) or information.
Copyright © 1998 Lucent Technologies Inc.
All Rights Reserved
Printed in U.S.A.
July 1998
AY98-025ISDN (Replaces AY98-020ISDN)
(Must accompany DS97-410ISDN, DS97-411ISDN, and DS97-412ISDN)
INTERNET:
E-MAIL:
N. AMERICA: Microelectronics Group, Lucent Technologies Inc., 555 Union Boulevard, Room 30L-15P-BA, Allentown, PA 18103
ASIA PACIFIC: Microelectronics Group, Lucent Technologies Singapore Pte. Ltd., 77 Science Park Drive, #03-18 Cintech III, Singapore 118256
CHINA:
JAPAN:
EUROPE:
OPTOIN
SCNT1
Figure 1. MLT Circuit Showing New Placement of Zener Diode (Z
PIN
A
is a 1.0 µF 10% tantalum chip capacitor, with a voltage rating of at least 16 V. C
+5 V
http://www.lucent.com/micro
[e-mail]
1-800-372-2447, FAX [phone] (In CANADA: 1-800-553-2448, FAX [phone])
Tel. [phone], FAX [phone]
Microelectronics Group, Lucent Technologies (China) Co., Ltd., A-F2, 23/F, Zao Fong Universe Building, 1800 Zhong Shan Xi Road,
Shanghai 200233 P . R. China Tel. [phone], ext. 316, FAX [phone]
Microelectronics Group, Lucent Technologies Japan Ltd., 7-18, Higashi-Gotanda 2-chome, Shinagawa-ku, Tokyo 141, Japan
Tel. [phone], FAX [phone]
Data Requests: MICROELECTRONICS GROUP DATALINE: Tel. [phone], FAX [phone]
Technical Inquiries: GERMANY: (49) 89 95086 0 (Munich), UNITED KINGDOM: (44) 1344 865 900 (Bracknell),
R8
17.8 k
2.2 M
R9
6
5
10 k
R10
7
8
FRANCE: (33) 1 48 83 68 00 (Paris), SWEDEN: (46) 8 600 7070 (Stockholm), FINLAND: (358) 9 4354 2800 (Helsinki),
ITALY: (39) 2 6601 1800 (Milan), SPAIN: (34) 1 807 1441 (Madrid)
U2
HCPL-0701
MLT CIRCUIT
2
3
C
1.0 µF
A
FOR NORTH AMERICAN
APPLICATIONS ONLY
1.0 µF
C15
137
137
R11
R12
Z
D
(PLACE THIS CAPACITOR AS
CLOSE AS POSSIBLE TO THE LH1465)
8
7
6
5
TC
RS
PD
COM
D
LH1465AB
(for example, Motorola * MMSZ4685T1).
U3
PR+
PR–
D
R
T
) and Capacitor (C
1
2
3
4
RING
TIP
A
R14
1.1 k
2 W
R15
1.1 k
2 W
is added to provide
A
)
July 1998
Advisory
5-7034(C)