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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)
For additional information, contact your Microelectronics Group Account Manager or the following:
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1-800-372-2447
, FAX 610-712-4106 (In CANADA:
1-800-553-2448
, FAX 610-712-4106)
ASIA PACIFIC: Microelectronics Group, Lucent Technologies Singapore Pte. Ltd., 77 Science Park Drive, #03-18 Cintech III, Singapore 118256
Tel. (65) 778 8833
, FAX (65) 777 7495
CHINA:
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. (86) 21 6440 0468
,
ext. 316
, FAX (86) 21 6440 0652
JAPAN:
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Tel. (81) 3 5421 1600
, FAX (81) 3 5421 1700
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Advisory
July 1998
Data Sheet Advisory
T7234, T7237, and T7256
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.
5-7034(C)
Figure 1. MLT Circuit Showing New Placement of Zener Diode (Z
D
) and Capacitor (C
A
)
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
D
(for example, Motorola* MMSZ4685T1).
Capacitor C
A
is a 1.0 μF
±
10% tantalum chip capacitor, with a voltage rating of at least 16 V. C
A
is added to provide
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.
R14
1.1 k
2 W
PR+
T
R
PR–
U3
LH1465AB
1
2
3
4
TC
RS
PD
COM
8
7
6
5
R12
137
C15
1.0 μF
R10
10 k
R8
17.8 k
+5 V
R9
2.2 M
5
6
8
2
3
U2
HCPL-0701
7
C
1.0 μF
MLT CIRCUIT
FOR NORTH AMERICAN
APPLICATIONS ONLY
R15
1.1 k
2 W
R11
137
(PLACE THIS CAPACITOR AS
CLOSE AS POSSIBLE TO THE LH1465)
Z
D
RING
TIP
SCNT1
OPTOIN
PIN