ATTL7581BC データシートの表示（PDF） - Agere -> LSI Corporation

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ATTL7581BC

Ringing Access Switch

Agere -> LSI Corporation 

L7581 Ringing Access Switch

Data Sheet

November 1999

Power Supplies

Protection

Both the 5 V and battery supply are brought onto the

L7581. The L7581 requires only the 5 V supply for

switch operation; that is, state control is powered exclu-

sively off of the 5 V supply. Because of this, the L7581

offers extremely low power dissipation, both in the idle

and active states.

The battery voltage is not used for switch state control.

The battery is used as a reference voltage by the inte-

grated secondary protection circuit. When the voltage

at TBAT or RBAT drops 2 V to 4 V below the battery, the

integrated SCR will trigger, thus preventing fault-

induced overvoltage situations at the TBAT/RBAT nodes.

Loss of Battery Voltage

As an additional protection feature, the L7581 monitors

the battery voltage. Upon loss of battery voltage, the

L7581 will automatically enter an all OFF state and

remain in that state until the battery voltage is restored.

The L7581 is designed so that the device will enter the

all OFF state if the battery rises above –10 V and will

remain off until the battery drops below –15 V.

Monitoring the battery for the automatic shutdown fea-

ture will draw a small current from the battery, typically

4 µA. This will add slightly to the overall power dissipa-

tion of the device.

Impulse Noise

Using the L7581 will minimize and possibly eliminate

the contribution to the overall system impulse noise

that is associated with ringing access switches.

Because of this characteristic of the L7581, it may not

be necessary to incorporate a zero cross switching

scheme. This ultimately depends upon the characteris-

tics of the individual system and is best evaluated at

the board level.

Integrated SLIC Protection

Diode Bridge/SCR

In the L7581Axx version, protection to the SLIC device

or other subsequent circuitry is provided by a combina-

tion of current-limited break switches, a diode bridge/

SCR clamping circuit, and a thermal shutdown mecha-

nism. In the L7581Bxx version, protection to the SLIC

device or other subsequent circuitry is provided by a

combination of current-limited break switches, a diode

bridge, and a thermal shutdown mechanism.

In both versions, during a positive lightning event, fault

current is directed to ground via steering diodes in the

diode bridge. Voltage is clamped to a diode drop above

ground. In the A version, negative lightning causes the

SCR to conduct when the voltage goes 2 V to 4 V more

negative than the battery, and fault currents are

directed to ground via the SCR and steering diodes in

the diode bridge.

Note that for the SCR to foldback or crowbar, the ON

voltage (see Table 10) of the SCR must be less nega-

tive than the battery reference voltage. If the battery

voltage is less negative than the SCR ON voltage, the

SCR will conduct fault currents to ground; however, it

will not crowbar.

In the B version, negative lightning is directed to battery

via steering diodes in the diode bridge.

For power cross and power induction faults, in both ver-

sions, the positive cycle of the fault is clamped a diode

drop above ground and fault currents steered to

ground. In the A version, the negative cycle will cause

the SCR to trigger when the voltage exceeds the bat-

tery reference voltage by 2 V to 4 V. When the SCR

triggers, fault current is steered to ground. In the B ver-

sion, the negative cycle of the power cross is steered to

battery.

Current Limiting

During a lightning event, the current that is passed

through the break switches and presented to the inte-

grated protection circuit and subsequent circuitry is lim-

ited by the dynamic current-limit response of the break

switches (assuming idle/talk state). When the voltage

seen at the TLINE/RLINE nodes is properly clamped by

an external secondary protector, upon application of a

1000 V 10 x 1000 pulse (LSSGR lightning), the current

seen at the TBAT/RBAT nodes will typically be a pulse of

magnitude 2.5 A and duration less than 0.5 µs.

8

Lucent Technologies Inc.

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