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L7556 Datasheet(PDF) 1 Page - Agere Systems |
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L7556 Datasheet(HTML) 1 Page - Agere Systems |
1 / 28 page Data Sheet January 2000 L7556, L7557 Low-Power SLICs with Battery Switch Features s Auxiliary input for second battery, and internal switch to enable its use to save power s Low active power (typical 125 mW during on-hook transmission) s Supports meter pulse injection s Spare op amp for meter pulse filtering s –16 V to –60 V power supply operation s Distortion-free on-hook transmission s Convenient operating states: — Forward powerup — Disconnect (high impedance) — 2-wire wink (zero loop voltage) s Adjustable supervision functions: — Off-hook detector with longitudinal rejection — Ground key detector — Ring trip detector s Independent, adjustable, dc and ac parameters: — dc feed resistance — Loop current limit — Termination impedance s Thermal protection Description These electronic subscriber loop interface circuits (SLICs) are optimized for low power consumption while providing an extensive set of features. The SLICs 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 SLICs 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 versions. 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. It 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 device is available in a 32-pin PLCC package. It is built by using a 90 V complementary bipolar inte- grated circuit (CBIC) process. |
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