LH1465AB

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 C15 1.0 µF R11 137 Ω (PLACE THIS CAPACITOR AS CLOSE AS POSSIBLE TO THE LH1465) LH1465AB 8 TC PR+ 7 RS T U3 6 PD R 5 COM PR– R14 1.1 kΩ 2W +5 V R10 10 kΩ 8 6 5 R9 R8 17.8 kΩ SCNT1 OPTOIN PIN U2 R12 137 Ω 2 3 CA 1.0 µF ZD 1 2 3 4 R15 1.1 kΩ 2W RING TIP 7 HCPL-0701 2.2 MΩ FOR NORTH AMERICAN APPLICATIONS ONLY 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 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 ZD (for example, Motorola* MMSZ4685T1). Capacitor CA is a 1.0 µF ±10%...