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

OPERATING

CONSIDERATIONS

PA46

GENERAL

Please read Application Note 1 "General Operating Consid-

erations" which covers stability, supplies, heat sinking, mount-

ing, current limit, SOA interpretation, and specification inter-

pretation. Visit www.apexmicrotech.com for design tools that

help automate tasks such as calculations for stability, internal

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.

CURRENT LIMIT

Current limiting is achieved by developing 0.83V on the

amplifiers current sense circuit by way of an internal tie to the

output drive (pin 5) and an external current sense line (pin 10).

A sense resistor R

current flowing from output drive.

0.83 – 0.05 * I

CL

R

I

CL

0.83

I

R

with a maximum practical value of 16

Ω. R

typical value of output resistance and affects the total possible

swing since it carries the load current. The swing reduction, V

R

can be established V

INPUT PROTECTION

The PA46 inputs are protected against common mode

voltages up to the supply rails, differential voltages up to

±16

volts and static discharge. Differential voltages exceeding 16

volts will be clipped by the protection circuitry. However, if

more than a few milliamps of current is available from the input

drive source, the protection circuitry could be destroyed. The

protection circuitry includes 300 ohm current limiting resistors

at each input. This security may be insufficient for severe

overdrive of the input. Adding external resistors to the applica-

tion which limits severe input overdrive current to 1mA, will

prevent damage.

STABILITY

The PA46 has sufficient phase margin when compensated

for unity gain to be stable with capacitive loads of at least 10nF.

However, the low pass circuit created by the sum-point (–in)

capacitance and the feedback network may add phase shift

and cause instabilities. As a rule, the sum-point load resis-

tance (input and feedback resistors in parallel) should be 1k

ohm or less. Alternatively, use a bypass capacitor across the

feedback resistor. The time constant of the feedback resistor

and bypass capacitor combination should match the time

constant of the sum-point resistance and sum-point capaci-

tance.

The PA46 is externally compensated and performance can

be tailored to the application. The compensation network C

R

avoid noise coupling to these high impedance nodes.

SAFE OPERATING AREA (SOA)

The MOSFET output stage of this power operational ampli-

fier has limitations from its channel temperature.

NOTE: The output is protected against transient flyback.

However, for protection against sustained, high energy flyback,

external fast-recovery diodes should be used.

SUPPLY TO OUTPUT DIFFERENTIAL, V

4

6

8 10

20

40

60

100

200

0.1

0.2

0.4

0.6

0.8

1.0

2.0

4.0

6.0

DC,

T

C

=

85

°C

DC,

T

C

=

125

°C

DC

200mS

100mS

PULSE CURVES @ 10% DUTY CYCLE MAX

SAFE OPERATING AREA

SHUTDOWN

Pin 3 (SHDN) will shut off the output stage when at least

90

µA is pulled from pin 3 to any voltage at least 3 volts less than

+V

BIAS CLASS OPTION FOR LOWER

QUIESCENT CURRENT

Normally pin 7 (I

(C

This results in lower quiescent current, but also class C

biasing of the output stage.

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.

PA46U REV. C FEBRUARY 2001

© 2001 Apex Microtechnology Corp.