P r o d u c t I n n o v a t i o n F r o m
PA83 • PA83A
GENERAL
±. The following capacitive and inductive loads are safe:
PleasereadApplicationNote±"GeneralOperatingConsider-
ations"whichcoversstability,supplies,heatsinking,mounting,
currentlimit,SOAinterpretation,andspecificationinterpretation.
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 contain a wealth of informa-
tion 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
currentversionofallApexPrecisionPowerproductdatasheets,
visit www.Cirrus.com.
±±S
±50V
±25V
±00V
75V
C(MAX)
.7 F
2.0µF
5.µF
60µF
ALL
L(MAX)
±.5H
2.5H
6.0H
30H
50V
ALL
2. Short circuits to ground are safe with dual supplies up to
±20V or single supplies up to ±20V.
3. Short circuits to the supply rails are safe with total supply
voltages up to ±20V, e.g. ±60V.
4. The output stage is protected against transient flyback.
However, for protection against sustained, high energy
flyback, external fast-recovery diodes should be used.
SAFE OPERATING AREA (SOA)
The bipolar output stage of this high voltage amplifier has
two distinct limitations.
INDUCTIVE LOADS
Two external diodes as shown in Figure ±, are required
to protect these amplifiers against flyback (kickbackꢀ pulses
exceeding the supply voltages of the amplifier when driving
inductiveloads. Forcomponentselection,theseexternaldiodes
must be very quick, such as ultra fast recovery diodes with
no more than 200 nanoseconds of reverse recovery time. Be
sure the diode voltage rating is greater than the total of both
supplies. 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.
±. The internal current limit, which limits maximum available
output current.
2. The second breakdown effect, which occurs whenever the
simultaneous collector current and collector-emitter voltage
SOA
200
150
A note of caution about the supply.The energy of the flyback
pulsemustbeabsorbedbythepowersupply.Asaresult,atran-
sientwillbesuperimposedonthesupplyvoltage,themagnitude
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.
INTERNAL CURRENT LIMIT
100
t = 0.5ms
SECOND BREAKDOWN
t = 1ms
70
t = 5ms
steady state
50
+VS
40
30
20
80
100
120
150
200
300
250
INTERNAL VOLTAGE DROP, SUPPLY TO OUTPUT (V)
–VS
exceed specified limits.
FIGURE 1. PROTECTION, INDUCTIVE LOAD
The SOA curves combine the effect of these limits. For a
given application, the direction and magnitude of the output
currentshouldbecalculatedormeasuredandcheckedagainst
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:
4
PA83U