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

OPERATING

CONSIDERATIONS

PA45

GENERAL

Please read the General Operating Considerations section,

which covers stability, supplies, heat-sinking, mounting, cur-

rent limit, SOA interpretation, and specification interpretation.

Additional information can be found in the application notes.

For information on the package outline, heatsink, and mount-

ing hardware, consult the “Accessories Information” and “Pack-

aging” mechanical data section of the data book.

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 8) and an external current sense line (pin 1).

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 PA45 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 PA45 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 PA45 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

DC,

T

C

=

85

°C

4.0

6.0

PULSE CURVES @ 10% DUTY CYCLE MAX

DC,

T

C

=

125

°C

200mS

DC

100mS

SAFE OPERATING AREA

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.

PA45U REV. B FEBRUARY 1998

© 1998 Apex Microtechnology Corp.