CPC7582

R05

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15

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 application note AN-144, Impulse

Noise Benefits of Line Card Access Switches. 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

Ω in series

with the ringing generator is recommended.

2.6 Power Supplies

Both a +5 V supply and battery voltage are connected

to the CPC7582. CPC7582 switch state control is

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

the CPC7582BC exhibits extremely low power

dissipation during both active and idle states.

The battery voltage is not used for switch control but

rather as a supply for the integrated secondary

protection circuitry. The integrated SCR is designed to

2.7 Battery Voltage Monitor

battery voltage. If battery voltage is lost, the CPC7582

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 system battery

voltage goes more positive than –10 V, and remains in

the all-off state until the battery voltage goes more

negative than –15 V. This battery monitor feature

draws a small current from the battery (less than 1

μA

typical) and will add slightly to the device’s overall

power dissipation.

2.8 Protection

2.8.1 Diode Bridge/SCR

The CPC7582 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

diode bridge.

In order for the SCR to crowbar or foldback, the on

voltage (see “Protection Circuitry Electrical

Specifications” on page 10) of the SCR must be less

supply 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 the

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

current to ground.

2.8.2 Current Limiting function

If a lightning strike transient occurs when the device is

in the talk state, the current is passed along the line to

the integrated protection circuitry and limited by the

dynamic current limit response of the active switches

during the talk state. During the talk state, when a

1000V 10x1000

μs pulse (GR-1089-CORE lightning)

is applied to the line though a properly clamped

magnitude of 2.5 A and a duration of less than 0.5

μs.

If a power-cross fault occurs with the device in the talk

state, the current is passed though break switches

SW1 and SW2 on to the integrated protection circuit

and is limited by the dynamic DC current limit

response of the two break switches. The DC current

limit, specified over temperature, is between 80 mA

and 425 mA, and the circuitry has a negative

temperature coefficient. As a result, if the device is

subjected to extended heating due to a power cross

increases. If the device temperature rises sufficiently,

the temperature shutdown mechanism will activate

and the device will enter the all-off state.

2.9 Temperature Shutdown

The thermal shutdown mechanism will activate when

the device temperature reaches a minimum of 110° C,

placing the device in the all-off state regardless of

logic input. During thermal shutdown mode, pin 7