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4

OPERATING

CONSIDERATIONS

PA15FL  •  PA15FLA

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

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

R

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.

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

capacitor is recommended. The compensation network C

must be mounted closely to the amplifier pins 8 and 9 to avoid

spurious oscillation.

FIGURE2.OVERVOLTAGEPROTECTION

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.

PA15FLU REV B FEBRUARY 2007 © 2007 Apex Microtechnology Corp.