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ATTL7581BC Datasheet(PDF) 7 Page - Agere Systems |
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ATTL7581BC Datasheet(HTML) 7 Page - Agere Systems |
7 / 16 page Lucent Technologies Inc. 7 Data Sheet November 1999 L7581 Ringing Access Switch Switching Behavior (continued) When using an L7581 in the make-before-break mode, during the ring-to-idle transition, for a period of up to one-half the ringing frequency, the ring break switch and the pnpn-type ring access switch can both be in the ON state. This is the maximum time after the logic signal at INRING has transitioned that the ring access switch is waiting for the next zero current cross so it can close. During this interval, current that is limited to the dc break switch current-limit value will be sourced from the ring node of the SLIC. This current is presented to the internal protection cir- cuit. If the SCR-type protector is used (A code), if by random probability the ring-to-idle transition occurs during a portion of the ring cycle when the ringing volt- age exceeds the protection circuit SCR turn-on voltage, and if current in excess of the SCR’s turn-on current is also available, the SCR may turn on. Once the SCR is triggered on, if the SLIC is capable of supplying current in excess of the holding current, the SCR may be latched on by the SLIC. The probability of this event depends on the character- istics of the given SLIC and of the holding current of the L7581A device. The SCR hold current distribution is designed to be safely away from the test limit of 80 mA. The higher the distribution, the lower the probability of the latch. If this situation is of concern for a given board design, either use the A series device in the break-before-make mode (eliminates the original 25 ms current pulse) or use a B series device (eliminates the SCR). Table 9. Make-Before-Break Operation Table 10. Break-Before-Make Operation INPUT TSD State Timing Break Switches 1 & 2 Ring Return Switch 3 Ring Access Switch 4 5 V 5 V/Float Power Ringing — Open Closed Closed 0 V 5 V/Float Make- before- break SW4 waiting for next zero current crossing to turn off, maximum time—one-half of ringing. In this transition state, current that is lim- ited to the dc break switch cur- rent-limit value will be sourced from the ring node of the SLIC. Closed Open Closed 0 V 5 V/Float Idle/Talk Zero cross current has occurred. Closed Open Open INPUT TSD State Timing Break Switches 1 & 2 Ring Return Switch 3 Ring Access Switch 4 5 V 5 V/Float Power Ringing — Open Closed Closed 5 V 0 V All Off Hold this state for ≤25 ms. SW4 waiting for zero current to turn off. Open Open Closed 0 V 0 V All Off Zero current has occurred and SW4 has opened. Transition on INPUT should occur during 25 ms hold. Open Open Open 0 V 5 V/Float Idle/Talk Release break switch pair. Closed Open Open |
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