PA92
GENERAL
Please read Application Note 1 "General Operating Consid-
erations" which covers stability, supplies, heat sinking, mount-
ing, current limit, SOA interpretation, and specification inter-
pretation. Visit www.apexmicrotech.com for design tools that
help automate tasks such as calculations for stability, internal
power dissipation, current limit; heat sink selection; Apex’s
complete Application Notes library; Technical Seminar Work-
book; and Evaluation Kits.
OPERATING
CONSIDERATIONS
INPUT PROTECTION
Although the PA92 can withstand differential voltages up to
±20V,
additional external protection is recommended. Low
leakage, low capacitance JFETs connected as diodes are
recommended (e.g. 2N4416, Q1-Q4 in Figure 2). The differen-
tial input voltage will be clamped to
±1.4V.
This is sufficient
overdrive to produce maximum power bandwidth.
POWER SUPPLY PROTECTION
Unidirectional zener diode transient suppressors are recom-
mended as protection on the supply pins. See Figure 2. The
zeners clamp transients to voltages within the power supply
rating and also clamp power supply reversals to ground.
Whether the zeners are used or not, the system power supply
should be evaluated for transient performance including power-
on overshoot and power-off polarity reversals as well as line
regulation.
Conditions which can cause open circuits or polarity rever-
sals on either power supply rail should be avoided or protected
against. Reversals or opens on the negative supply rail is
known to induce input stage failure. Unidirectional transzorbs
prevent this, and it is desirable that they be both electrically and
physically as close to the amplifier as possible.
CURRENT LIMIT
For proper operation, the current limit resistor (R
CL
) must be
connected as shown in the external connection diagram. For
optimum reliability the resistor value should be set as high as
possible. The value is calculated as follows; with the maximum
practical value of 16 ohms.
.65
R
CL
=
I
LIM
SAFE OPERATING AREA (SOA)
The MOSFET output stage of this power operational ampli-
fier has two distinct limitations:
1. The current handling capability of the MOSFET geometry
and the wire bonds.
2. The junction temperature of the output MOSFETs.
NOTE: The output stage is protected against transient flyback.
However, for protection against sustained, high energy flyback,
external fast-recovery diodes should be used.
STABILITY
The PA92 is externally compensated and performance can
be tailored to the application. Use the graphs of small signal
response and power response as a guide. The compensation
capacitor C
C
must be rated at 500V working voltage. An NPO
capacitor is recommended. The compensation network C
C
R
C
must be mounted closely to the amplifier pins 4 and 5 to avoid
spurious oscillation.
SAFE OPERATING CURVES
The safe operating area curves define the maximum addi-
tional internal power dissipation the amplifier can tolerate
when it produces the necessary output to drive an external
load.
8
6
OUTPUT CURRENT FROM +V
S
OR –V
S
, (A)
QUIESCENT CURRENT REDUCTION
When pin 3 (I
Q
) is shorted to pin 5 (CC2) the AB biasing of
the output stage is disabled. This lowers quiescent power but
also raises distortion since the output stage is then class C
biased. The output stage bias current is nominally set at 1mA.
Pin 3 may be left open if not used.
+V
S
DC, T
C
= 25°C
4
2
200mS
Z1
10
1
.8
.6
.4
.3
.2
.1
.08
.06
.04
10
0m
S
T
–IN
Q1
Q2
+IN
Q3
1
11, 12
6
C
=
T
C
=
85
°
C
PA92
Q4
2
7, 8
Z2
–V
S
12
5
°
C
FIGURE 2.
OVERVOLTAGE
PROTECTION
20
30 40
60 80 100
200 300
500
SUPPLY TO OUTPUT DIFFERENTIAL, V
S
–V
O
(V)
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.
PA92U REV. C MAY 2000 © 2000 Apex Microtechnology Corp.
ETC [ ETC ]
