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R04

CPC7592

the device to the all-off state and a high impedance (Z)

state for normal operation. This requires the use of an

open-collector or open-drain type buffer.

2.6 Ringing Switch Zero-Cross Current Turn Off

After the application of a logic input to turn SW4 off,

the ringing switch is designed to delay the change in

state until the next zero-crossing. Once on, the switch

requires a zero-current cross to turn off, and therefore

should not be used to switch a pure DC signal. The

switch will remain in the on state no matter the logic

input until the next zero crossing. These switching

characteristics will reduce and possibly eliminate

overall system impulse noise normally associated with

ringing switches. See IXYS IC Division’s application

note AN-144, Impulse Noise Benefits of Line Card Access

Switches for more information. The attributes of ringing

switch SW4 may make it possible to eliminate the

need for a zero-cross switching scheme. A minimum

impedance of 300

 in series with the ringing

generator is recommended.

2.7 Power Supplies

Both a +5 V supply and battery voltage are connected

to the CPC7592. Switch state control is powered

exclusively by the +5 V supply. As a result, the

CPC7592 exhibits extremely low power consumption

during active and idle states.

Although battery power is not used for switch control, it

is required to supply trigger current for the integrated

internal protection circuitry SCR during fault

conditions. This integrated SCR is designed to

Because the battery supply at this pin is required to

source trigger current during negative overvoltage

fault conditions at tip and ring, it is important that the

net supplying this current be a low impedance path for

high speed transients such as lightning. This will

permit trigger currents to flow enabling the SCR to

activate and thereby prevent a fault induced negative

2.8 Battery Voltage Monitor

battery voltage. If system battery voltage is lost, the

CPC7592 immediately enters the all-off state. It

remains in this state until the battery voltage is

restored. The device also enters the all-off state if the

battery voltage rises more positive than about –10 V

with respect to ground and remains in the all-off state

until the battery voltage drops below approximately

–15 V with respect to ground. This battery monitor

feature draws a small current from the battery (less

than 1

A typical) and will add slightly to the device’s

overall power dissipation.

This monitor function performs properly if the

CPC7592 and SLIC share a common battery supply

origin. Otherwise, if battery is lost to the CPC7592 but

pins via the internal protection circuitry SCR trigger

current path.

2.9 Protection

2.9.1 Diode Bridge/SCR

The CPC7592 uses a combination of current limited

break switches, a diode bridge/SCR clamping circuit,

and a thermal shutdown mechanism to protect the

SLIC device or other associated circuitry from damage

during line transient events such as lightning. During a

positive transient condition, the fault current is

conducted through the diode bridge to ground via

ground. During a negative transient of 2 to 4 V more

or the diode bridge.

In order for the SCR to crowbar (or foldback), the

SCR’s on-voltage (see “Protection Circuitry Electrical

Specifications” on page 9) must be less than the applied

is unable to source the trigger current, the SCR will not

crowbar.

For power induction or power-cross fault conditions,

the positive cycle of the transient is clamped to a diode

drop above ground and the fault current directed to

ground. The negative cycle of the transient will cause

the SCR to conduct when the voltage exceeds the

the fault current to ground.

Note: The CPC7592xB does not contain the

protection SCR but instead uses diodes to clamp both

polarities of a transient fault. These diodes direct the