PA83A Datasheet, PDF(4/4 Page) Cirrus Logic – HIGH VOLTAGE POWER OPERATIONAL AMPLIFIERS

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OPERATING

CONSIDERATIONS

PA83 â¢ PA83A

GENERAL

Please read Application Note 1 "General Operating Con-

siderations" which covers stability, supplies, heat sinking,

mounting, current limit, SOA interpretation, and speciï¬cation

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 speciï¬c 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 ampliï¬er 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 speciï¬ed limits.

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1. The following capacitive and inductive loads are safe:

Â±VS

150V

125V

100V

75V

50V

C(MAX)

.7 F

2.0ÂµF

5.ÂµF

60ÂµF

ALL

L(MAX)

1.5H

2.5H

6.0H

30H

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. Â±60V.

4. The output stage is protected against transient ï¬yback.

However, for protection against sustained, high energy

ï¬yback, external fast-recovery diodes should be used.

INDUCTIVE LOADS

Two external diodes as shown in Figure 1, are required

to protect these ampliï¬ers against ï¬yback (kickback) pulses

exceeding the supply voltages of the ampliï¬er 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 ï¬yback 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 ï¬yback

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.

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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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