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347

OPERATING

CONSIDERATIONS

PA83 • PA83A

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 bipolar output stage of this high voltage amplifier has

two distinct limitations.

1. The internal current limit, which limits maximum available

output current.

2. The second breakdown effect, which occurs whenever the

simultaneous collector current and collector-emitter voltage

exceed specified limits.

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. However, the

following guidelines may save extensive analytical efforts:

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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.

PA83U REV O NONEMBER 2004 © 2004 Apex Microtechnology Corp.

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1. The following capacitive and inductive loads are safe:

±V

S

C(MAX)

L(MAX)

150V

.7 F

1.5H

125V

2.0µF

2.5H

100V

5.µF

6.0H

75V

60µF

30H

50V

ALL

ALL

2. Short circuits to ground are safe with dual supplies up to

120V or single supplies up to 120V.

3. Short circuits to the supply rails are safe with total supply

voltages up to 120V, e.g. ±60V.

4. The output stage is protected against transient flyback.

However, for protection against sustained, high energy

flyback, external fast-recovery diodes should be used.

INDUCTIVE LOADS

Two external diodes as shown in Figure 1, are required

to protect these amplifiers against flyback (kickback) pulses

exceeding the supply voltages of the amplifier when driving

inductive loads. For component selection, these external diodes

must be very quick, such as ultra fast recovery diodes with

no more than 200 nanoseconds of reverse recovery time. Be

sure the diode voltage rating is greater than the total of both

supplies. The diode will turn on to divert the flyback energy

into the supply rails thus protecting the output transistors from

destruction due to reverse bias.

A note of caution about the supply. The energy of the flyback

pulse must be absorbed by the power supply. As a result, a tran-

sient will be superimposed on the supply voltage, the magnitude

of the transient being a function of its transient impedance and

current sinking capability. If the supply voltage plus transient

exceeds the maximum supply rating or if the AC impedance

of the supply is unknown, it is best to clamp the output and the

supply with a zener diode to absorb the transient.