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PA08(2004) Просмотр технического описания (PDF) - Apex Microtechnology

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PA08
(Rev.:2004)

POWER OPERATIONAL AMPLIFIER

Apex Microtechnology

PA08 Datasheet PDF : 4 Pages

1 2 3 4

PA08 • PA08A

OPERATING

CONSIDERATIONS

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)

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The output stage of most power ampliﬁers has two 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.

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.

1. Under transient conditions, the following capacitive and

inductive loads are safe with the current limits set to the

maximum:

±VS

150V

125V

100V

75V

50V

C(MAX)

.4µF

.9µF

2µF

10µF

100µF

L(MAX)

280mH

380mH

500mH

1200mH

13H

2. The ampliﬁer can handle any EMF generating or reactive

load and short circuits to the supply rails or simple shorts

to common if the current limits are set as follows:

±VS

150V

125V

100V

75V

50V

SHORT TO ±VSC,

C, L, OR EMF LOAD

20mA

27mA

42mA

67mA

130mA

SHORT TO

COMMON

67mA

90mA

130mA

200mA

These simpliﬁed limits may be exceeded with further analysis

using the operating conditions for a speciﬁc application.

3. 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 from 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. 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.

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PROTECTION, INDUCTIVE LOAD PROTECTION, OVERVOLTAGE

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.

INPUT PROTECTION

The input is protected against common mode voltages up to

the supply rails and differential voltages up to ±50V. Increased

protection against differential input voltages can be obtained by

adding 2 resistors, 2 capacitors and 4 diode connected FETs

as shown in Figure 2.

CURRENT LIMITING

Proper operation requires the use of two current limit resis-

tors, connected as shown in the external connection diagram.

The minimum value for RCL is 3.24Ω. However, for optimum

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

“General Operating Considerations” section of the handbook

for current limit adjust details.

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