CPC1593

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5

R01

Functional Description

The CPC1593 is an optically coupled Solid State

Relay composed of an input LED, two output

MOSFET switches, and a photovoltaic array with

operational management circuitry that integrates

switch control, an active current limit with excess

power regulation and thermal supervision circuitry.

Designed specifically for switching AC loads, the

CPC1593 is ideal for controlling in-rush current

by means of it’s integrated active current limit with

excess power regulation feature. The CPC1593 may

also be used for switching low voltage DC loads.

Biasing the input LED to activate the output

switches while providing for proper performance

over the operating temperature range and during

load faults is dependent on adherence to the limits

given for the Input Control Current parameter in

the Recommended Operating Conditions table.

Configuring the input drive circuit to provide a

nominal LED current approximately equal to the

typical value listed in the table will provide best

overall performance.

The CPC1593 has two different operating

configurations: (1) unidirectional “DC Only”, and

(2) bidirectional “AC/DC”. When configured for

unidirectional DC-only operation, the device is limited

to switching load voltages having a known fixed

polarity but when configured for AC/DC operation,

the CPC1593 is capable of polarity independent

voltage switching. The advantage of operating the

device in the AC/DC configuration is the flexibility of

switching AC load voltages while restricting in-rush

current to the maximum current limit value shown in

the Electrical Characteristics table without sacrificing

fault protection.

Fault tolerance management at the CPC1593 load

terminals is accomplished using a combination

of current limiting, switch power regulation and

thermal supervision. These features autonomously

provide protection during fault conditions, then

disengage once the fault clears allowing the device

to automatically resume normal operation without

external intervention.

Faults originate from a number of causes ranging

from equipment malfunctions such as load

integrity failure or load voltage supply failure to

environmentally initiated events such as power line

contact with outside cabling or ground bounce due to

a nearby lightning strike. Generally when a potentially

damaging fault condition occurs, it presents itself as

an elevated voltage resulting in excess load current

through the switch. Therefore, in this situation, the

first line of defense is to limit the increasing load

current.

Active current limiting circuitry within the CPC1593

provides protection for itself, the printed circuit board

(PCB) traces and the load by restricting the surge

current to a tolerable level. Limiting the fault load

current regulates the maximum power across all of

the load components external to the CPC1593. The

consequence of limiting the power dissipation in the

external load components is that the power load is

shifted to the CPC1593. This is easily observed by

monitoring the increasing voltage across the load

terminals while in current limit.

Under these conditions the maximum power

dissipation rating of the CPC1593 can be exceeded.

To prevent this, the device must regulate the

power dissipation of the output switches. This is

accomplished by a significant reduction of the load

current anytime the current limit function is active

and the voltage across the load terminals exceeds

the internally set Over-Voltage Threshold (V

load current is then reduced to less than 100

A and

held at this level until the voltage across the load

terminals decreases to less than V

the outputs will resume normal operation. Should the

fault condition persist, current limiting will begin again

and the process will repeat. Continually cycling into

current limit and over-voltage load current throttling

(I

excessive temperature rise within the device, driving

it into thermal supervision.

Releasing the input control to deactivate the relay

during current limiting or over-voltage load current

throttling will reset these functions causing the relay

to resume normal operation when the input control is

re-asserted.