Am79D2251

The Intelligent Access voice chipsets integrate all functions of the subscriber line for two subscriber lines. One or more of two chip types are used to implement the linecard; an ISLIC device and a dual ISLAC device. These Am79D2251 provide the following basic functions: 1. The ISLIC device: A high voltage, bipolar IC that drives the subscriber line, maintains longitudinal balance and senses line conditions. 2. The dual ISLAC device: A low voltage CMOS IC that provides conversion and DSP functions for 2 channels. Complete schematics of linecards using the Intelligent Access voice chipsets for internal and external ringing are shown in Figure 4 and Figure 5.

Am79D2251 uses reliable, bipolar technology to provide the power necessary to drive a wide variety of subscriber lines. It can be programmed by the ISLAC device to operate in eight different modes that control power consumption and signaling modes. This enables it to have full control over the subscriber loop. The ISLIC device is customized to be used exclusively with the ISLAC device as part of a multiple-line chipset. The ISLIC device requires only +5 V power and the battery supplies for its operation.

Am79D2251 implements a linear loop-current feeding method with the enhancement of intelligent thermal management in a controlled manner. This limits the amount of power dissipated on the ISLIC chip by dissipating excess power in external resistors.