CPC7594 datasheet(18/20 Pages) IXYS

18 / 20 page

INTEGRATED CIRCUITS DIVISION

www.ixysic.com

R04

CPC7594

If presented with a short duration transient such as a

lightning event, the thermal shutdown feature will

typically not activate. But in an extended power-cross

event, the device temperature will rise and the thermal

shutdown mechanism will activate forcing the switches

to the all-off state. At this point the current measured

into TLINE or RLINE will drop to zero. Once the device

enters thermal shutdown it will remain in the all-off

state until the temperature of the device drops below

the de-activation level of the thermal shutdown circuit.

This permits the device to autonomously return to

normal operation. If the transient has not passed,

current will again flow up to the value allowed by the

dynamic DC current limiting of the switches and

heating will resume, reactivating the thermal shutdown

mechanism. This cycle of entering and exiting the

thermal shutdown mode will continue as long as the

fault condition persists. If the magnitude of the fault

condition is great enough, the external secondary

protector will activate shunting the fault current to

ground.

2.11 External Protection Elements

The CPC7594 requires only over voltage secondary

protection on the loop side of the device. The

integrated protection feature described above negates

the need for additional external protection on the SLIC

side. The secondary protector must limit voltage

transients to levels that do not exceed the breakdown

voltage or input-output isolation barrier of the

CPC7594. A foldback or crowbar type protector is

recommended to minimize stresses on the CPC7594.

Consult IXYS IC Division’s application note, AN-100,

“Designing Surge and Power Fault Protection Circuits for

Solid State Subscriber Line Interfaces” for equations

related to the specifications of external secondary

protectors, fused resistors and PTCs.

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