ATTL7581BC 查看數據表（PDF） - Agere -> LSI Corporation

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ATTL7581BC

Ringing Access Switch

Agere -> LSI Corporation 

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

INPUT TSD

5 V 5 V/Float

0 V 5 V/Float

0 V 5 V/Float

State

Timing

Break

Ring Return

Switches 1 & 2 Switch 3

Power

—

Ringing

Open

Closed

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

Idle/Talk Zero cross current has occurred.

Closed

Open

Ring Access

Switch 4

Closed

Closed

Open

Table 10. Break-Before-Make Operation

INPUT TSD

5 V 5 V/Float

5V

0V

0V

0V

0 V 5 V/Float

State

Timing

Break

Ring Return

Switches 1 & 2 Switch 3

Power

Ringing

All Off

—

Hold this state for ≤25 ms. SW4

waiting for zero current to turn off.

Open

Open

Closed

Open

All Off Zero current has occurred and

SW4 has opened. Transition on

INPUT should occur during 25 ms

hold.

Idle/Talk Release break switch pair.

Open

Closed

Open

Open

Ring Access

Switch 4

Closed

Closed

Open

Open

Lucent Technologies Inc.

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