PA51 • PA51A
GENERAL
P r o d u c t I n n o v a t i o nF r o m
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.Cirrus.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 con-
tain 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 Precision
Power product models, consult the "Evaluation Kit" section
for details. For the most current version of all Apex Precision
Power product data sheets, visit www.Cirrus.com.
1. Under transient conditions, capacitive and dynamic* induc-
tive loads up to the following maximums are safe:
±V
S
40V
35V
30V
25V
20V
15V
CAPACITIVE LOAD
I
LIM
= 5A
I
LIM
= 10A
400µF
200µF
800µF
400µF
1,600µF
800µF
5.0mF
2.5mF
10mF
5.0mF
20mF
10mF
INDUCTIVE LOAD
I
LIM
= 5A
I
LIM
= 10A
11mH
4.3mH
20mH
5.0mH
35mH
6.2mH
50mH
15mH
400mH
20mH
**
100mH
SAFE OPERATING AREA (SOA)
The output stage of most power amplifiers has three 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.
3. The junction temperature of the output transistors.
10
* If the inductive load is driven near steady state conditions,
allowing the output voltage to drop more than 8V below the
supply rail with I
LIM
= 10A or 15V below the supply rail with
I
LIM
= 5A while the amplifier is current limiting, the inductor
should be capacitively coupled or the current limit must be
lowered to meet SOA criteria.
** Second breakdown effect imposes no limitation but thermal
limitations must still be observed.
2. The amplifier can handle any EMF generating or reactive
load and short circuits to the supply rail or shorts to common
if the current limits are set as follows at T
C
= 85°C.
±V
S
45V
40V
35V
30V
25V
20V
15V
SHORT TO ±V
S
C, L, OR EMF LOAD
0.1A
0.2A
0.3A
0.5A
1.2A
1.5A
2.0A
SHORT TO
COMMON
1.3A
1.5A
1.6A
2.0A
2.4A
3.0A
4.0A
SOA
t=
T
OUTPUT CURRENT FROM +V
S
OR – V
S
(A)
7.0
5.0
3.0
2.0
1.5
1.0
0.7
0.5
0.3
0.2
1m
TH
ER
C
MA
L
T
C
T
=1
=2
s
C
=8
5°C
5°C
t=
25
°C
5
15
20
30
40 50
70 80
7
10
SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE V
S
– V
O
(V)
The SOA curves combine the effect of of all limits for this
Power Op Amp. For a given application, the direction and
magnitude of the output current should be calculated or mea-
sured and checked against the SOA curves. This is simple
for resistive loads but more complex for reactive and EMF
generating loads. The following guidelines may save extensive
analytical efforts.
5m
s
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. How-
ever, for protection against sustained, high energy flyback,
external fast-recovery diodes should be used.
ste
ady
sta
te
CURRENT LIMIT
Proper operation requires the use of two current limit resis-
tors, connected as shown in the external connection diagram.
The minimum value for R
CL
is .06 ohm, 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.
4
PA51U
CIRRUS [ CIRRUS LOGIC ]
