I
NTEGRATED
C
IRCUITS
D
IVISION
CPC1563
www.ixysic.com
5
R01
Functional Description
The CPC1563 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. It
was designed specifically for telecom products and
applications requiring switching of moderate level DC
loads or AC loads having a moderate DC offset.
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 CPC1563 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 CPC1563 is capable of polarity independent
voltage switching. The advantage of operating the
device in the DC-only configuration is the ability to
switch larger load currents while the advantage of
operating in the AC/DC configuration is the flexibility
of switching AC load voltages or DC load voltages of
either polarity.
Fault tolerance management at the CPC1563 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 CPC1563
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 CPC1563. The
consequence of limiting the power dissipation in the
external load components is that the power load is
shifted to the CPC1563. 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 CPC1563 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
TH
). The
load current is then reduced to less than 100A,
and held at this level until the voltage across the
load terminals decreases to less than V
TH
at which
point 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
L
<100A) with a long duration fault can
result in 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.
