PA97DR Ver la hoja de datos (PDF) - Apex Microtechnology
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PA97DR Datasheet PDF : 4 Pages
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OPERATING
CONSIDERATIONS
PA97DR
GENERAL
Please read the “General Operating Considerations” section,
which covers stability, supplies, heatsinking, mounting, current
limit, SOA interpretation, and specification interpretation. Ad-
ditional information can be found in the application notes. For
information on the package outline, heatsinks, and mounting
hardware, consult the “Accessory and Package Mechanical
Data” section of the handbook.
CURRENT LIMIT
The PA97DR has no provision for current limiting the
output.
COMMON MODE INPUT RANGE
Operational amplifiers are usually designed to have a com-
mon mode input voltage range that approximates the power
supply voltage range. However, to keep the cost as low as
possible and still meet the requirements of most applications
the common mode input voltage range of the PA97DR is re-
stricted. The input pins must always be a least 30V from either
supply voltage but never more than 500V. This means that the
PA97 cannot be used in applications where the supply voltages
are extremely unbalanced. For example, supply voltages
of +800V and –100V would not be allowed in an application
where the non-inverting pin is grounded because in normal
operation both input pins would be at 0V and the difference
voltage between the positive supply and the input pins would
be 800V. In this kind of application, however, supply voltages
+500V and -100V does meet the input common mode voltage
range requirements since the maximum difference voltage
between the inputs pins and the supply voltage is 500V (the
maximum allowed). The output has no such restrictions on
its voltage swing. The output can swing within 24V of either
supply voltage regardless of value so long as the total supply
voltage does not exceed 900V.
INPUT PROTECTION
Although the PA97DR can withstand differential input
voltages up to ±20V, additional external protection is recom-
mended. In most applications 1N4148 or 1N914 signal diodes
are sufficient (D1, D2 in Figure 2a). In more demanding appli-
cations where low leakage or low capacitance are of concern
2N4416 or 2N5457-2N5459 JFETs connected as diodes will
be required (Q1, Q2 in Figure 2b). In either case the input
differential voltage will be clamped to ±.7V. This is sufficient
overdrive to produce maximum power bandwidth. Note that
this protection does not automatically protect the amplifier from
excessive common mode input voltages.
POWER SUPPLY PROTECTION
Unidirectional zener diode transient suppressors are recom-
mended as protection on the supply pins. 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 reversal as well as line regulation.
Conditions which can cause open circuits or polarity reversals
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.
EXTERNAL COMPONENTS
The compensation capacitor Cc must be rated for the total
supply voltage. 10pF NPO (COG)capacitor rated at 1kV is
recommended.
Of equal importance is the voltage rating and voltage coef-
ficient of the gain setting feedback resistor. Typical voltage
ratings of low wattage resistors are 150 to 250V. Up to 900 V
can appear across the feedback resistor. High voltage rated
resistors can be obtained. However a 1 megohm feedback
resistor composed of five 200k resistors in series will produce
the proper voltage rating.
CAUTIONS
The operating voltages of the PA97DR are potentially lethal.
During circuit design develop a functioning circuit at the lowest
possible voltages. Clip test leads should be used for "hands
off" measurements while troubleshooting. With no internal
current limit, proper choice of load impedance and supply
voltage is required to meed SOA limitiations. An output short
circuit will destroy the amplifier within milliseconds.
STABILITY
The PA97DR is stable at gains of 10 or more with a NPO
(COG) compensation capacitor of 10pF. The compensation
capacitor, Cc, in the external connections diagram must be
rated at 1000V working voltage and mounted closely to pins 4
and 6 to prevent spurious oscillation. A compensation capaci-
tor less than 10pF is not recommended.
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PA97U REV F JUNE 2007 © 2007 Apex Microtechnology Corp.
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