APEX MICROTECHNOLOGY CORPORATION • 5980 NORTH SHANNON ROAD • TUCSON, ARIZONA 85741 • USA • APPLICATIONS HOTLINE: 1 (800) 546-2739

4

OPERATING

CONSIDERATIONS

PA03 • PA03A

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.

MOUNTING PRECAUTIONS

The PA03 copper base is very soft and easily bent. Do not

put any stress on the mounting ears of this package. This calls

for caution when pushing the amplifier into certain types of

packaging foam and particularly when inserting the device into

a socket. Insert the amplifier into the socket only by pushing

on the perimeter of the package lid. Pushing the unit into the

socket by applying pressure to the mounting tabs will bend

the base due to the high insertion force required. The base

will then not contact the heatsink evenly resulting in very poor

heat transfer. To remove a unit from a socket, pry the socket

away from the heatsink so that the heatsink will support the

amplifier base evenly. Recommended mounting torque is 8–10

in.-lbs. (.9–1.13 N•m).

SAFE OPERATING AREA (SOA)

Due to the internal (non-adjustable) current limit of the PA03,

worst case power dissipation calculations must assume cur-

rent capability of 46 amps. Application specific circuits should

be checked against the SOA curve when relying upon current

limit for fault protection.

SAFE OPERATING AREA CURVES

Second breakdown limitations do apply to the PA03 but are

less severe, since junction temperature limiting responds within

10ms. Stress levels shown as being safe for more than 10ms

duration will merely cause thermal shutdown.

Under normal operating conditions, activation of the thermal

shutdown is a sign that the internal junction temperatures have

reached approximately 175°C. Thermal shutdown is a short

term safety feature. If the conditions remain that cause thermal

shutdown, the amplifier will oscillate in and out of shutdown,

creating peak high power stresses, destroying useful signals,

and reducing the reliability of the device.

BALANCE CONTROL

The voltage offset of the PA03 may be externally adjusted

to zero. To implement this adjustment install a 100 to 200 ohm

potentiometer between pins 11 and 12 and connect the wiper

arm to the positive supply. Bypass pins 11 and 12 each with

at least a .01µF ceramic capacitor.

If the optional adjust provision is not used, connect both

pins 11 and 12 to the positive supply.

OUTPUT STAGE SHUTDOWN

The entire power stage of the PA03 may be disabled us-

ing one of the circuits shown in Figure 1. There are many

applications for this function. One is a load protection based

on power delivered to the load or thermal rise. Another one is

conservation of power when using batteries. The control voltage

requirements accommodate a wide variety logic drivers.

1. CMOS operating at +5V can drive the control pins di-

rectly.

2. CMOS operating at greater than 5V supplies need a voltage

divider.

3. TTL logic needs a pull up resistor to +5V to provide a swing

to the fully disabled voltage (3.5V). When not using the

shutdown feature, connect both pins 3 and 4 to common.

PHASE COMPENSATION

At low gain settings an external compensation capacitor is

required to insure stability. In addition to the resistive feed-

back network, roll off or integrating capacitors must also be

considered. A frequency of 1 MHz is most appropriate to cal-

culate gain. Operation at gains below 10, without the external

compensation capacitor opens the possibility of oscillations

near output saturation regions when under load, the improper

operation of the thermal shutdown circuit. This can result in

amplifier destruction.

At gains of 10 or more:

1. No external components are required.

2. Typical slew rate will be 8V/µs.

3. Typical phase margin will be 70°.

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EXTERNAL CONNECTIONS

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The internal substrate contains beryllia (BeO).

Do not break the seal. If accidentally broken, do

not crush, machine, or subject to temperatures

in excess of 850°C to avoid generating toxic

fumes.

CAUTION