INTEGRATED CIRCUITS DIVISION
8www.ixysic.com R02
CPC1560
2. Introduction
The CPC1560 is an optically coupled Solid State
Rela y (SSR) t hat is self- biased from the load sup ply.
An optional external charge storage capacitor is used
to speed up SSR turn-on. The CPC1560 also
incorporates current limiting and a thermal shutdo wn
f eature in the output circuit ry, making the device ideal
for use in harsh conditions.
3. Functional Description
Internally, the device is composed of an LED, a
photovoltaic array with control circuitry, and two
MOSFET output switches.
Input current to the LED is t he signal to t urn-on the
SSR’ s output MOSFET s witches. The LED illuminates
the photov oltaics, which provide current to the gates of
the output MOSFETs, causing them to conduct. When
utilizing CEXT, the charge delivered to the MOSFET
gates initially includes the charge stor ed in th e
e x ternal capacitor, causing the SSR to conduct more
quickly than if only the photo v oltaic current were used.
When the Load Voltage (VL) is first applied to the
inactiv e outputs, the e xternal storage capacitor begins
to charge. To ensure proper operation, the storage
capacitor should be equal to or g reat er t han the tot al
gate capacitance of the two output MOSFET switches.
Charge from the load voltage is passed through
bootstrap diodes , which prevent the charge from
escaping and discharging the capacitor thr ough the
MOSFET output switch when the SSR is turned on.
The input control current is applied, then the charge is
transferred from the storage capacitor through the
internal NPN bipolar transistor along with the charge
from the photo voltaic, to the MOSFET gates to
accomplish a rapid turn-on. After the MOSFETs hav e
turned on and the capacitor has discharged current
from the photo voltaic continues to flow into the gates,
keeping t he MOSFETs turned on.
When the input control current is remov ed, gate
current from the photovoltaic stops flowing and the
PNP bipolar transistor turns on, discharging the
MOSFET gates. The MOSFETs ar e now off. At this
point, with load voltage applied, the capacitor begins
recharging for the next turn on cycle.
The non-conducting, optical coupling space between
the LED and the photovoltaics provides 3750Vrms of
isolation between the control input and the switched
output of the CPC1560.
Important things t o note about the oper a tion of the
CPC1560:
•The device is designed to maintain its guaranteed
operating char acteristics with DC input control
current (IF) in the range of 2.5mA to 10mA (see
“Recommended Operating Conditions” on page 4). The
device will operate at input currents above and belo w
this range , but device operat ing char act eristics over
the operating temper ature range are not guar anteed.
•There is a minimum LED input current required for
the de vice to shut off: 0.1mA at 25°C (see “Electrical
Specifications” on page 5).
•The output switch will only withstand a maxim um o f
60 v olts across its t erminals bef or e breaking do wn
(see“Absolute Maximum Ratings” on page 3). Maximum
v olt age gener ally occurs wh en the output is o ff.
The CPC1560 has two different operating
configurations: unidirectional DC-only configur ation,
and bidirectional A C/DC configuration.
In the unidirectional DC-only configuration, the de vice
switches load v oltages with a fixed polarity, while in the
A C/DC configuration it can switch voltages with either
positive or negative polarities.
The adv antag e of oper ating t he device in the DC-only
configuration is the abilit y to switch larger load
currents. The advantage of operating it in the AC/DC
configuration is the f lexibility of switching load v oltages
of either polarity.
4. Device Configuration
4.1 LED Resistor
To assure proper operation of the CPC1560, the LED
resistor selection should comply with the
recommended operating conditions. Although the LED
is capable of being op er at ed up to the absolu te
maximum rat ings, this is not recommended. Oper ating
the LED bey ond the recommended oper ating
conditions may prevent the current limit and thermal
shutdown functions fro m performing properly. The
equation to calculate the maxim um resistor value is:
•IF_MIN = Minimum Input Cont rol Curr ent
•VIN_MIN = Minim um Input Pow er Source
•VLOW_MAX = Maximum Logic Level Low Voltage
•VF_MAX = Maximum Forward Voltage Drop of LED
•RLED_MAX = Maximum Input Resistor to LED
RLED_MAX = VIN_MIN - VLOW_MAX - VF_MAX
IF_MIN
VIN
+
VF
-
VLOW
RLED