LH1465AB Datasheet, PDF (1/14 Pages) Agere Systems – LH1465AB/AAE ISDN dc Termination IC Data Sheet Advisory

Advisory
July 1998
LH1465AB/AAE ISDN dc Termination IC
Data Sheet Advisory
Application Circuit
Replace Figure 11 on page 10 of the LH1465AB/AAE data sheet with the figure shown below.
MLT CIRCUIT
+5 V
R8
17.8 kΩ
R10
10 kΩ
8
6
SCNT1
OPTOIN
PIN
5
R9 7
2.2 MΩ
U2
2
3
HCPL-0701
CA
1.0 µF
C15
1.0 µF
R11
137 Ω
R12
137 Ω
ZD
(PLACE THIS CAPACITOR AS
CLOSE AS POSSIBLE TO THE LH1465)
LH1465AB
8 _TC
PR+ ¹
7 _RS
6 _PD
U3
T2
R3
5 _COM
PR– ⁴
R14
1.1 kΩ
2W
R15
1.1 kΩ
2W
FOR NORTH AMERICAN
APPLICATIONS ONLY
RING
TIP
5-7034(C)
Figure 1. MLT Circuit Showing New Placement of Zener Diode (ZD) and Capacitor (CA)
In the ILOSS mode (refer to ANSI T1.601 1992, Section 6.5.2), the NT generates a scrambled, framed, 2B1Q
signal 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 sig-
nal 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 ZD (for example, Motorola*
MMSZ4685T1). Capacitor CA is a 1.0 µF ±10% tantalum chip capacitor, with a voltage rating of at least 16 V.
CA 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.