PA15FL Datasheet, PDF (4/4 Pages) Cirrus Logic – HIGH VOLTAGE POWER OPERATIONAL AMPLIFIERS

PA15FL  •  PA15FLA
OPERATING
CONSIDERATIONS
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.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
Workbook; and Evaluation Kits.
CURRENT LIMIT
For proper operation, the current limit resistor (R_CL) must be
connected as shown in the external connection diagram. The
minimum value is 2 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.

.6 
_RCL
=     
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.
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INPUT PROTECTION
Although the PA15FL can withstand differential input voltages
up to ±25V, additional external protection is recommended. In
most applications 1N4148 or 1N914 signal diodes are sufficient
(D1-D4 in Figure 2a). In more demanding applications where
low leakage or low capacitance are of concern 2N4416 or
2N5457-2N5459 JFETs connected as diodes will be required
(Q1-Q4 in Figure 2b). In either case the input differential volt-
age 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. 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 are
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.
STABILITY
The PA15FL has sufficient phase margin to be stable with
most capacitive loads at a gain of 10 or more, using the rec-
ommended phase compensation.
The PA15FL 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_CR_C
must be mounted closely to the amplifier pins 8 and 9 to avoid
spurious oscillation.
FIGURE 2. OVERVOLTAGE PROTECTION
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PA15FLU REV B FEBRUARY 2007  © 2007 Apex Microtechnology Corp.