library; Technical Seminar Workbook; and Evaluation Kits.
PARALLEL CONFIGURATION CONSIDERATIONS
LOSSES
The PA74 and PA76 utilize a parallel configuration to achieve
the desired current output requirements.The parallel configura-
tion 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.
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.
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
100Hz
1KHz
5KHz
10KHz
15KHz
Supply Current
18mA
20mA
32mA
50mA
75mA
SOA
OUTPUT CURRENT FROM +V
S
or -V
S
, (A)
10
TWO AMPLIFIERS LOADED
DC, T
C
= 25°C
ONE AMPLIFIER
LOADED
1.0
DC, T
C
= 85°C
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.
70
60
50
40
30
20
10
0
0
25
50
75
100
CASE TEMPERATURE, T
C
(°C)
125
ONE AMPLIFIER LOADED
POWER DERATING
TWO AMPLIFIERS LOADED
0.1
1.0
10
100
SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE, V
S
- V
O
(V)
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 a Apex Microtechnology 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.
4
INTERNAL POWER DISSIPATION, P (W)
PA74-76U
PA74/76 • PA74A/76A
NEED TECHNICAL HELP? CONTACT APEX SUPPORT!
For all Apex Microtechnology product questions and inquiries, call toll free 800-546-2739 in North America.
For inquiries via email, please contact apex.support@apexanalog.com.
International customers can also request support by contacting their local Apex Microtechnology Sales Representative.
To find the one nearest to you, go to www.apexanalog.com
IMPORTANT NOTICE
Apex Microtechnology, Inc. has made every effort to insure the accuracy of the content contained in this document. However, the information is subject to change
without notice and is provided "AS IS" without warranty of any kind (expressed or implied). Apex Microtechnology reserves the right to make changes without further
notice to any specifications or products mentioned herein to improve reliability. This document is the property of Apex Microtechnology and by furnishing this informa-
tion, Apex Microtechnology grants no license, expressed or implied under any patents, mask work rights, copyrights, trademarks, trade secrets or other intellectual
property rights. Apex Microtechnology owns the copyrights associated with the information contained herein and gives consent for copies to be made of the informa-
tion only for use within your organization with respect to Apex Microtechnology integrated circuits or other products of Apex Microtechnology. This consent does not
extend to other copying such as copying for general distribution, advertising or promotional purposes, or for creating any work for resale.
APEX MICROTECHNOLOGY PRODUCTS ARE NOT DESIGNED, AUTHORIZED OR WARRANTED TO BE SUITABLE FOR USE IN PRODUCTS USED FOR
LIFE SUPPORT, AUTOMOTIVE SAFETY, SECURITY DEVICES, OR OTHER CRITICAL APPLICATIONS. PRODUCTS IN SUCH APPLICATIONS ARE UNDER-
STOOD TO BE FULLY AT THE CUSTOMER OR THE CUSTOMER’S RISK.
Apex Microtechnology, Apex and Apex Precision Power are trademarks of Apex Microtechnolgy, Inc. All other corporate names noted herein may be trademarks
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