PA08 • PA08A
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 Consider-
ations" 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, cur-
rent 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 avail-
able 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.
±V
S
150V
125V
100V
75V
50V
SHORT TO ±V
SC,
C, L, OR EMF LOAD
20mA
27mA
42mA
67mA
130mA
SHORT TO
COMMON
67mA
90mA
130mA
200mA
200mA
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.
However, for protection against sustained, high energy
flyback, external fast-recovery diodes should be used.
INDUCTIVE LOADS
Two external diodes as shown in Figure 1, are required
to protect these amplifiers from flyback (kickback) pulses
exceeding the supply voltages of the amplifier when driving
inductive loads. For component selection, these external diodes
must be very quick, such as ultra fast recovery diodes with no
more than 200 nanoseconds of reverse recovery time. The
diode will turn on to divert the flyback energy into the supply
rails thus protecting the output transistors from destruction due
to reverse bias.
Fig. 1
+V
S
IN4936 OR
UES1106
SAFE OPERATING AREA (SOA)
200
OUTPUT CURRENT FROM
+V
S
OR –V
S
(mA)
150
100
80
50
40
30
t=
t=
ste
t=
ad
ys
5m
s
e
t=
1m
0.5m
s
s
20
0s
tat
Fig. 2
+IN
100pf/200V
150KΩ
Q1
Q2
Q3
Q4
_
20
80
100
120
150 170
250
300
200
SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE (V)
The output stage of most power amplifiers has two 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.
The SOA curves combine the effect of these limits. 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. However, the
following guidelines may save extensive analytical efforts.
1. Under transient conditions, the following capacitive and
inductive loads are safe with the current limits set to the
maximum:
–IN
–V
S
150KΩ
100pf/200V
+
PROTECTION, INDUCTIVE LOAD
PROTECTION, OVERVOLTAGE
A note of caution about the supply. The energy of the flyback
pulse must be absorbed by the power supply. As a result, a tran-
sient will be superimposed on the supply voltage, the magnitude
of the transient being a function of its transient impedance and
current sinking capability. If the supply voltage plus transient
exceeds the maximum supply rating or if the AC impedance of
the supply is unknown, it is best to clamp the output and the
supply with a zener diode to absorb the transient.
INPUT PROTECTION
The input is protected against common mode voltages up to
the supply rails and differential voltages up to ±50V. Increased
protection against differential input voltages can be obtained by
adding 2 resistors, 2 capacitors and 4 diode connected FETs
as shown in Figure 2.
±V
S
150V
125V
100V
75V
50V
C(MAX)
.4µF
.9µF
2µF
10µF
100µF
L(MAX)
280mH
380mH
500mH
1200mH
13H
CURRENT LIMITING
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 3.24Ω. 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.
2. The amplifier can handle any EMF generating or reactive
load and short circuits to the supply rails or simple shorts
to common if the current limits are set as follows:
4
PA08U
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