PA94 datasheet(3/4 Pages) APEX

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TYPICAL PERFORMANCE

GRAPHS

PA94

INTERNAL POWER DISSIPATION AND HEATSINK SELECTION

With the unique combination of high voltage and speed

of the PA94, traditional formulas for heatsink selection will

falsely lower the apparent power handling capability of this

ampliﬁer. To more accurately predict operating temperatures

use Power Design1 revision 10 or higher, or use the following

procedure:

Find internal dissipation (PD) resulting from driving the

load. Use Power Design or refer to Apex Applications Note

1, General Operating Considertaions, paragraph 7. Find total

quiescent power (PD

Q) by multiplying 0.024A by VSS (total

supply voltage). Find output stage quiescent power (PD

QOUT)

by multiplying 0.00012 by V

SS.

Calculate a heatsink rating which will maintain the case at

85°C or lower.

Where: T

C = maximum case temperature allowed

A = maximum ambient temperature encountered

Calculate a heatsink rating which will maintain output transistor

junctions at 150°C or lower.

Where: T

J = maximum junction temperature allowed.

ØJC = AC or DC thermal resistance from the speciﬁcation

table.

Use the larger heatsink of these two calculations.

Power Design is an Excel spreadsheet available free from

www.apexmicrotech.com

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Tc - Ta

ØSA =

-0.1°C/W

PD + PD

J - Ta - (PD + PDQOUT) *RØJC

ØSA =

-0.1°C/W

PD + PD

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