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4

OPERATING

CONSIDERATIONS

PA75

This data sheet has been carefully checked and is believed to be reliable, however, no responsibility is assumed for possible inaccuracies or omissions. All specifications are subject to change without notice.

PA75U REV D MARCH 2006 © 2006 Apex Microtechnology Corp.

GENERAL

Please read Application Note 1 “General Operating Consider-

ations” which covers stability, supplies, heatsinking, mounting,

SOA interpretation, and specification interpretation. Visit www.

apexmicrotech.com for design tools that help automate tasks

such as calculations for stability, internal power dissipation,

heatsink selection; Apex’s complete Application Notes library;

Technical Seminar Workbook; and Evaluation Kits.

STABILITY CONSIDERATIONS

All monolithic power op amps use output stage topologies

that present special stability problems. This is primarily due to

non-complementary (both devices are NPN) output stages with

a mismatch in gain and phase response for different polarities

of output current. It is difficult for the op amp manufacturer to

optimize compensation for all operating conditions.

SAFE OPERATING AREA (SOA)

The SOA curves combine the effect of all limits for this power

op amp. For a given application, the direction and magnitude

of the output current should be calculated or measured and

checked against the SOA curves. This is simple for resistive

loads but more complex for reactive and EMF generating

loads.

THERMAL CONSIDERATIONS

The PA75CD and CX have a large exposed copper heat

tab to which the monolithic is directly attached. The PA75CD

and CX may require a thermal washer, which is electrically

insulating since the tab is directly tied to -VS. This can result

in a thermal impedance RCS of up to 1˚C/W or greater.

The PA75CC has a large exposed integrated copper heatslug

to which the monolithic is directly attached. The solder connec-

tion of the heatslug to a minimum of 1 square inch foil area of

the printed circuit board will result in thermal performance of

25°C/W junction to air rating of the PA75CC. Solder connec-

tion to an area of 1 to 2 square inches of foil is required for

minimal power applications

Where the PA75CC is used in higher power applications,

it is necessary to use surface mount techniques of heatsink-

ing. Surface mount techniques include the use of a surface

mount fan in combination with a surface mount heatsink on

the backside of the FR4/ PC board with through hole thermal

vias. Other highly thermal conductive substrate board materials

are available for maximum heat sinking.

MOUNTING PRECAUTIONS

1. Always use a heat sink. Even unloaded the PA75 can dis-

sipate up to .4 watts.

2. Avoid bending the leads. Such action can lead to internal

damage.

3. Always fasten the tab of the CD and CX package to the heat

sink before the leads are soldered to fixed terminals.

4. Strain relief must be provided if there is any probability of

axial stress to the leads.