CPC1560GS datasheet(9/14 Pages) CLARE

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CPC1560

R00F

PRELIMINARY

4.2 Storage Capacitor

The CPC1560 requires the use of an external

capacitor (CEXT) to meet the device’s specifications.

This external storage capacitor enables the relay to

turn on quickly by holding a reservoir of charge to be

transferred to the gates of the MOSFET pair. The

capacitor must have a minimum working voltage

greater than the load voltage, and must be connected

from pin 8 (C+), the capacitor’s positive voltage

terminal, to pin 5 (C-), the capacitor’s negative voltage

terminal.

Proper selection of the external capacitor begins with

the recommended range provided in the

“Recommended Operating Conditions” on page 4, and the

maximum voltage at the CPC1560 outputs, including

transients and faults. The nominal value of the

capacitor needs to be chosen so that when the effects

of tolerance, temperature coefficient, and (for some

types of capacitor) derating due to bias voltage are

accounted for, the capacitor’s value remains within the

recommended range over the operational conditions

of the end product.

5. Operational Behavior

5.1 Operating Frequency

5.1.1 Duty Cycle/Power Dissipation

Equation 1 shows the relationship between power

dissipation, operating frequency, and duty cycle for the

CPC1560 device. From this equation, it can be seen

that both switching frequency (fswitch) and duty cycle

(D) contribute to power dissipation. The first one by

generating switching losses, and the second one by

generating ON losses. Switching losses are those

caused by changes in the energy state of the load

components when the device is switching on and off

(i.e. ERISE and EFALL), and ON losses are those

caused by the flow of current (IL) through the part’s

on-resistance (RON) when it is switched on.

Because a higher operating frequency translates into

higher power consumed by the part, care must be

taken to limit its value in order to protect the device

from exceeding its maximum power rating. When

doing this, both the maximum allowed power

dissipation in the part and the ON duty cycle,

D=tON / (tON+tOFF), must be taken into consideration.

5.1.2 Temperature Effects

When setting the operating frequency of the

CPC1560, the user must also take into account power

dissipation over temperature.

5.1.3 Elements of Operating Frequency

In addition to ambient temperature, the maximum

frequency of the CPC1560 is also determined by the

MOSFET’s turn-on and turn-off times and the load

voltage rise and fall times as follows:

Where 1/3 is a multiplication factor for temperature

and process variations.

5.2 Switching Losses

During the transition intervals of the switching process,

the load components change energy states, which

results in switching losses as the energy passes

through the MOSFETs. This energy transfer is

manifested in the form of heat dissipation and must be

taken into consideration.

Energy is transferred during the turn-off intervals. This

energy, called Erise, will be absorbed by the MOSFET

output switches, and if present parasitic load

capacitance and the protection device.

Energy is also transferred during the turn-on intervals

and is called Efall. This energy will be absorbed by the

MOSFET output switches, which is why this energy

should be limited to the “peak turn-on energy” values

specified in the Absolute Maximum Ratings Table of

this datasheet.

The user of the CPC1560 device must understand the

details of the load behavior and keep in mind the

device’s recommended operating conditions in order

to adequately size the load components and protect

the application circuit.

The average power of the CPC1560 output MOSFET

for any specific application and for any load type given

by Equation 1 and repeated here is:

From this equation we can see how the switching

losses (ERISE and EFALL), together with the “on

losses,” contribute to the CPC1560’s output power

dissipation.

The user must also know that the recommended

operating conditions for IL, fSWITCH, load capacitance

(1) Pavg = IL

2 • R

ON • D + fswitch • (ERISE + EFALL)

(2)

fMAX =

(tON + tOFF)

-1

(3) Pavg = IL

2 • R

ON • D + fswitch • (ERISE + EFALL)

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