CPC7514

R06

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13

3.6 External Protection Elements

The CPC7514 requires only over-voltage secondary

protection on the high-voltage side of the switch.

Additional external protection may be required on the

low-voltage side of the switch if the threshold of the

high-voltage side protector exceeds the safe operation

of the low-voltage side components. Because the fault

current seen by the low-voltage side protector is

limited by the switch’s active current limit circuitry, the

low-voltage side protector need not be as capable as

that of the high-voltage side protector. The

high-voltage side protector must limit voltage

transients to levels that do not exceed the breakdown

voltage or input-output isolation barrier of the

CPC7514. A foldback or crowbar type protector on the

high-voltage side is recommended to minimize

stresses on the CPC7514.

3.7 Thermal Design Assessment

A successful design utilizing the CPC7514 Quad High

Voltage Analog Switch Array is dependent on careful

consideration of the application’s environment and the

device’s thermal constraints. For matters regarding the

electrical design, this is simply a case of following the

parameters provided in the preceding tables and for

many this will be sufficient. However, those designers

wishing to push the operational limits envelope with

higher switch current and/or higher ambient operating

temperatures will need to consider the thermal

performance.

Being a real physical device the CPC7514 has a finite

thermal capability that when properly considered will

ensure appropriate behavior and performance.

Determination of the thermal constraint is easily

accomplished using the following power equations:

and

from the “VDD Voltage Supply Specifications” on

page 7 while the power dissipated by the switches is

the sum of the concurrent active switches. Total switch

power is the sum of the maximum current through

each active switch times the On-Resistance of the

The second equation is used to calculate the

maximum ambient temperature that the device can be

operated in based on the calculated total power of the

first equation;

T, the junction temperature rise of the

CPC7514 from ambient; and



impedance of the device package are used to

determine the maximum operating ambient

temperature.

Using the junction temperature rise equation

T=T

reduces to:

To avoid entering thermal shutdown, the value for the

maximum junction temperature was set to 110

C.

Conversely, it is possible to rework the equations to

determine the maximum switch current for a maximum

ambient current.

When using the individual switches of the CPC7514

within their allowable operating region, no restrictions

are placed on any other switch.

DD

+

=

T



JA

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=

–

–





–

=