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

4

OPERATING

CONSIDERATIONS

PA74/76 • PA74A/PA76A

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.

PA74–76U REV C NOVEMBER 2004 © 2004 Apex Microtechnology Corp.

GENERAL

Please read Application Note 1 "General Operating Consider-

ations" which covers stability, supplies, heatsinking, mounting,

SOA interpretation, and specification interpretation. Visit www.

apexmicrotech.com for design tools that help automate tasks

such as calculations for stability, internal power dissipation,

heatsink selection; Apex's complete Application Notes library;

Technical Seminar Workbook; and Evaluation Kits.

STABILITY CONSIDERATIONS

All monolithic power op amps use output stage topologies

that present special stability problems. This is primarily due to

non-complementary (both devices are NPN) output stages with

a mismatch in gain and phase response for different polarities

of output current. It is difficult for the opamp manufacturer to

optimize compensation for all operating conditions.

SAFE OPERATING AREA (SOA)

The SOA curves combine the effect of all limits for this power

op amp. 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.

THERMAL CONSIDERATIONS

Thermal grease or an Apex TW03 thermal washer, RCS = .1

to .2°C/W, is the only recommended interface for the PA74/76.

Internal power dissipation increases directly with frequency

therefore it is critical to sufficiently heat sink the PA74 and

PA76. Even unloaded the PA74 and PA76 can dissipate up

to 3 watts while running at higher frequencies.

���

���������������������

�������������

������

���

���

��

���

���

��

����������������������������������������

�����

�����

PARALLEL CONFIGURATION CONSIDERATIONS

LOSSES

The PA74 and PA76 utilize a parallel configuration to

achieve the desired current output requirements. The paral-

lel configuration inherently creates internal losses due to

circulating currents. The circulating currents generate power

losses through the current sharing resistors when delivering

current to the load.

SUPPLY CURRENT

The parallel configuration used in the PA74 and PA76 also

generates supply currents while high voltage sign waves

are seen at the output. Listed below are the supply currents

expected while running at a particular frequency and when VO

≈ 15Vpp, note that the outputs are not loaded.

Frequency

Supply Current

100Hz

18mA

1KHz

20mA

5KHz

32mA

10KHz

50mA

15KHz

75mA

SATURATION OPERATION

The parallel configuration used in the PA74 and PA76 is

sensitive to operation in the saturation region. The PA74 and

PA76 may exhibit large peak currents; this is mainly due to

thermal protection limitations.

�

��

��

��

��

��

��

��

��������������

�

��

��

��

���

���

���������������������

��������������������

�������������������