PA89 Ver la hoja de datos (PDF) - Cirrus Logic
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PA89 Datasheet PDF : 5 Pages
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PA89 • PA89A
Product Innova tionFrom
GENERAL
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; heat sink selection; Apex Precision
Power’s complete Application Notes library;Technical Seminar
Workbook; and Evaluation Kits.
STABILITY
Although the PA89 can be operated at unity gain, maximum
slew rate and bandwidth performance was designed to be
obtained at gains of 10 or more. Use the small signal response
and phase response graphs as a guide. In applications where
gains of less than 10 are required, use noise gain compensa-
tion to increase the phase margin of the application circuit as
illustrated in the typical application drawing.
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.
SOA
100
10mS
50
25°C
100mS
30
15
125°C
85°C
10
5
T = TCASE
3
100
200 300
500 800 1000 1200
SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE, VS – VO (V)
SAFE OPERATING CURVES
The safe operating area curves define the maximum ad-
ditional internal power dissipation the amplifier can tolerate
when it produces the necessary output to drive an external
load. This is not the same as the absolute maximum internal
power dissipation listed elsewhere in the specification since the
quiescent power dissipation is significant compared to the total.
EXTERNAL COMPONENTS
The very high operating voltages of the PA89 demand con-
sideration of two component specifications rarely of concern in
building op amp circuits: voltage rating and voltage coefficient.
The compensation capacitance CC must be rated for the
full supply voltage range. For example, with supply voltages
of ±500V the possible voltage swing across CC is 1000V. In
addition, a voltage coefficient less than 100PPM is recom-
mended to maintain the capacitance variation to less than
5% for this example. It is strongly recommended to use the
highest quality capacitor possible rated at least twice the total
supply voltage range.
Of equal importance are the voltage rating and voltage coef-
ficient of the gain setting resistances. Typical voltage ratings of
low wattage resistors are 150 to 250V. In the above example
1000V could appear across the feedback resistor. This would
require several resistors in series to obtain the proper voltage
rating. Low voltage coefficient resistors will insure good gain
linearity. The wattage rating of the feedback resistor is also of
concern. A 1 megohm feedback resistor could easily develop
1 watt of power dissipation.
Though high voltage rated resistors can be obtained,
a 1 megohm feedback resistor comprised of five 200Kohm,
1/4 watt metal film resistors in series will produce the proper
voltage rating, voltage coefficient and wattage rating.
CURRENT LIMIT
For proper operation the current limit resistor (RCL) must be
connected as shown in the external connection diagram. The
minimum value is 3.5 ohm, however 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
150 ohms.
.7
RCL = ILIM
When setting the value for RCL allow for the load current as
well as the current in the feedback resistor. Also allow for the
temperature coefficient of the current limit which is approxi-
mately -0.3% /°C of case temperature rise.
CAUTIONS
The operating voltages of the PA89 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.
POWER SUPPLY PROTECTION
Unidirectional zener diode transient absorbers 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 reversals 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.
4
PA89U
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