APEX MICROTECHNOLOGY CORPORATION • 5980 NORTH SHANNON ROAD • TUCSON, ARIZONA 85741 • USA • APPLICATIONS HOTLINE: 1 (800) 546-2739

4

OPERATING

CONSIDERATIONS

PA01 • PA73

GENERAL

Please read Application Note 1 "General Operating Con-

siderations" which covers stability, supplies, heat sinking,

mounting, current limit, SOA interpretation, and specification

interpretation. Visit www.apexmicrotech.com for design tools

that help automate tasks such as calculations for stability, in-

ternal power dissipation, current limit and heat sink selection.

The "Application Notes" and "Technical Seminar" sections

contain a wealth of information on specific types of applications.

Package outlines, heat sinks, mounting hardware and other

accessories are located in the "Packages and Accessories"

section. Evaluation Kits are available for most Apex product

models, consult the "Evaluation Kit" section for details. For

the most current version of all Apex product data sheets, visit

www.apexmicrotech.com.

SAFE OPERATING AREA (SOA)

The output stage of most power amplifiers has three distinct

limitations:

1. The current handling capability of the transistor geometry

and the wire bonds.

2. The second breakdown effect which occurs whenever the

simultaneous collector current and collector-emitter voltage

exceeds specified limits.

3. The junction temperature of the output transistors.

The SOA curves combine the effect of these limits. 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.

line. Make sure the load line does not cross the 0.5ms limit

and that excursions beyond any other second breakdown

line do not exceed the time label, and have a duty cycle of

no more than 10%.

For other waveform outputs, manual load line plotting

is recommended. Applications Note 22, SOA AND LOAD

LINES, will be helpful. A Spice type analysis can be very

useful in that a hardware setup often calls for instruments

or amplifiers with wide common mode rejection ranges.

2. EMF generating or reactive load and short circuits to the

supply rail or shorts to common are safe if the current limits

are set as follows at T

SHORT TO ±V

S

SHORT TO

±V

S

C, L, OR EMF LOAD

COMMON

34V

.58A

1.1A

30V

.46A

1.4A

25V

.61A

1.7A

20V

.86A

2.1A

15V

1.3A

2.9A

3. The output stage is protected against occaisional transient

flyback. However, for protection against sustained, high

energy flyback, external fast-recovery diodes should be

used.

CURRENT LIMIT

Proper operation requires the use of two current limit resis-

tors, connected as shown, in the external connection diagram.

The minimum value for R

reliability it should be set as high as possible. Refer to the

“General Operating Considerations” section of the handbook

for current limit adjust details.

��

��

��

��

�� �� ��

��

��

��

��

��

��

���

���

���

���

���

���

���������

����������

�������

�����������������������������

�������

�������

���������

����������

1

Note 1. Power Design is a self-extracting Excel spreadsheet

available free from www.apexmicrotech.com

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.

PA01-73U REV R MARCH 2005 © 2005 Apex Microtechnology Corp.