PA07 Datasheet, PDF(4/4 Page) Cirrus Logic – FET INPUT POWER OPERATIONAL AMPLIFIERS

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OPERATING

CONSIDERATIONS

PA07 â¢ PA07A

GENERAL

Please read Application Note 1 "General Operating Con-

siderations" which covers stability, supplies, heat sinking,

mounting, current limit, SOA interpretation, and speciï¬cation

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;

Apexâs complete Application Notes library; Technical Seminar

Workbook; and Evaluation Kits.

SAFE OPERATING AREA (SOA)

The output stage of most power ampliï¬ers has three distinct

limitations:

1. The current handling capability of the wire bonds.

2. The second breakdown effect which occurs whenever the

simultaneous collector current and collector-emitter voltage

exceed speciï¬ed limits.

3. The junction temperature of the output transistors.

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SAFE OPERATING AREA CURVES

The SOA curves combine the effect of these limits. For a

given application, the direction and magnitude of the output

current should be calculated or measured and checked against

the SOA curves. This is simple for resistive loads but more

complex for reactive and EMF generating loads. However, the

following guidelines may save extensive analytical efforts.

1. For DC outputs, especially those resulting from fault condi-

tions, check worst case stress levels against the new SOA

graph.

For sine wave outputs, use Power Design1 to plot a load

line. Make sure the load line does not cross the 0.5ms limit

and that excursions beyond any other second breakdown

line do not exceed the time label, and have a duty cycle of

no more than 10%.

For other waveform outputs, manual load line plotting is

recommended. Applications Note 22, SOA AND LOAD

LINES, will be helpful. A Spice type analysis can be very

useful in that a hardware setup often calls for instruments

or ampliï¬ers with wide common mode rejection ranges.

2. The ampliï¬er can handle any reactive or EMF generating

load and short circuits to the supply rail or common if the

current limits are set as follows at TC = 85Â°C:

SHORT TO Â±VS

SHORT TO

Â±VS

C, L, OR EMF LOAD

COMMON

50V

.21A

.61A

40V

.3A

.87A

30V

.46A

1.4A

20V

.87A

2.5A

15V

1.4A

4.0A

These simpliï¬ed limits may be exceeded with further analysis

using the operating conditions for a speciï¬c application.

3. The output stage is protected against transient ï¬yback.

However, for protection against sustained, high energy

ï¬yback, external fast-recovery diodes should be used.

THERMAL SHUTDOWN PROTECTION

The thermal protection circuit shuts off the ampliï¬er when

the substrate temperature exceeds approximately 150Â°C. This

allows heatsink selection to be based on normal operating

conditions while protecting the ampliï¬er against excessive

junction temperature during temporary fault conditions.

Thermal protection is a fairly slow-acting circuit and therefore

does not protect the ampliï¬er against transient SOA violations

(areas outside of the TC = 25Â°C boundary). It is designed to

protect against short-term fault conditions that result in high

power dissipation within the ampliï¬er. If the conditions that

cause thermal shutdown are not removed, the ampliï¬er will

oscillate in and out of shutdown. This will result in high peak

power stresses, will destroy signal integrity and reduce the

reliability of the device.

CURRENT LIMIT

Proper operation requires the use of two current limit resis-

tors, connected as shown in the external connections diagram.

reliability it should be set as high as possible. Refer to the

âGeneral Operating Considerationsâ section of the handbook

for current limit adjust details.

1 Note 1. Power Design is a self-extracting Excel spreadsheet

available free from www.apexmicrotech.com

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