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LUCL9312AP-D Datasheet(PDF) 5 Page - Agere Systems |
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LUCL9312AP-D Datasheet(HTML) 5 Page - Agere Systems |
5 / 40 page Data Sheet July 2001 Forward Battery SLIC and Ringing Relay for TR-57 Applications L9312 Line Interface and Line Access Circuit Agere Systems Inc. 5 Description (continued) The switch point is a function of the user-programmed dc current limit and the magnitude of the auxiliary bat- tery. Switching from the high-voltage to low-voltage battery is quiet, without interruption of the dc loop cur- rent, thus preventing any impulse noise generation at the switch point. Design equations for the switch point and a graph showing loop/battery current versus loop resistance are given in the dc Characteristics in the Applications section of this data sheet. If the user does not want to provide an auxiliary battery, the design of the L9312 battery switch allows use of a power control resistor at the auxiliary battery input. This scheme will not reduce short-loop, off-hook power dis- sipation, but it will control power dissipation on the SLIC by sharing power among the SLIC, power resis- tor, and dc loop. However, in most cases, without the auxiliary battery, the power dissipation capabilities of the 44-pin PLCC package are adequate so that the power control resistor will not be needed. Design equa- tions for power control options are given in the dc Char- acteristics section of this data sheet. The L9312 is a forward battery only SLIC that supports on-hook transmission. A low-power scan mode is available to reduce idle mode on-hook power. This mode is realized by using a scan clamp circuit. In low-power scan mode: s The scan clamp circuitry is active. s Loop closure is active. s All ac transmission, dc feed, and other supervision circuits, including ring trip, are shut down. s Thermal shutdown is active. s Low battery sense shutdown is on. s On-hook transmission is disabled. A forward disconnect mode, where all circuits are turned off and power is denied to the loop, is also pro- vided. During this mode, the NSTAT supervision output will read on-hook. In the ring mode, the line break switches are opened and the power ring access switches are closed. In this mode, the ring trip detector in the SLIC is active and all other detectors and the tip/ring drive amplifiers are turned off to conserve power. Make-before-break or break-before-make switching is achievable during ring cadence or ring trip. Toggling directly into or directly out of the ring mode table will give make-before-break switching. To achieve break- before-make switching, go to an intermediate all-off state (use forward disconnect state) before entering the ring mode or before leaving the ring mode. See the Switching Behavior section of this data sheet for more details on switching behavior. Voltage transients or impulse noise associated with ring cadence or ring trip are minimized or eliminated with the L9312, thus possibly eliminating the need for external zero-cross switching circuitry. Both the ring trip and loop closure supervision func- tions are included. Loop closure threshold is set by applying a voltage source to the LCTH input. The volt- age source may be an external voltage source or derived from the SLIC VREF output. A programmable external voltage source may be used to provide soft- ware control of the loop closure threshold. Design equations for the loop closure threshold are given in the Supervision section of this data sheet. Hysteresis is included. The ring trip detector requires only a single-pole filter at the input. This will minimize the required number of external components. To help minimize device power dissipation, the ring trip detector is active only during the power ring mode. Ring trip and loop supervision status outputs appear in a common output pin, NSTAT. NSTAT is an unlatched supervision output; thus, an interrupt-based control scheme may be used. The dc current limit is set in the active modes via an applied voltage source. The voltage source may be an external voltage source. The voltage may be derived via a resistor divider network from the VREF SLIC out- put. A programmable external voltage source may be used to provide software control of the loop closure threshold. Design equations for this feature are given in the dc Characteristics section of this data sheet. Pro- gramming range is 10 mA to 45 mA. Overhead is programmable in the active modes via an applied voltage source. The voltage source may be an external voltage source or derived via a resistor divider network from the VREF SLIC output. A programmable external voltage source may be used to provide software control of the overhead voltage. The rate of change of the overhead voltage may be controlled by use of a single external capacitor at the CF1 node. If the rate of change is uncontrolled, there may be audible noise associated with this transition. Design equations for this feature are given in the dc Characteristics section of this data sheet. If the overhead is not programmed via a resistor, the device develops a default overhead adequate for a 3.14 dBm overload into 900 Ω. For the default over- head, OVH is connected to ground. |
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