L7557

Stresses in excess of the Absolute Maximum Ratings can cause permanent damage to the device. These are absolute stress ratings only. Functional operation of the device is not implied at these or any other conditions in excess of those given in the operational sections of the data sheet. Exposure to Absolute Maximum Ratings for extended periods can adversely affect device reliability.

These electronic subscriber loop interface circuits (SLICs) are optimized for low power consumption while providing an extensive set of features.

The L7557 include an auxiliary battery input and a built-in switch. In short-loop applications, they can be used in high battery to present a high on-hook volt-age, and then switched to low battery to reduce off-hook power.

The L7557 also include a summing node for meter pulse injection to 2.2 Vrms. A spare, uncommitted op amp is included for meter pulse filtering.The switched battery is applied to the power amplifi-ers of the device. There are two ersions. The L7556 has the battery switch completely under processor control. The L7557 can automatically switch to lower battery when appropriate and includes hysteresis to avoid frequent switching. To make the switch silent, an external capacitor can be added to slow the tran-sition.

The L7556 is suited for applications serving only short loops, where a high on-hook voltage is required for compatibility with preexisting standards.

The L7557 is suited for applications where a full loop range is needed, but low short-loop power is desired. L7557 is a much lower-cost solution than a switching reg-ulator, and also occupies much less PCB area, need-ing only a battery filter capacitor and a diode for implementation.

The L7557 is available in a 32-pin PLCC package. L7557 is built by using a 90 V complementary bipolar inte-grated circuit (CBIC) process.