Specifications and information are subject to change without notice

WJ Communications, Inc

• Phone 1-800-WJ1-4401 • FAX: 408-577-6621 • e-mail: sales@wj.com • Web site: www.wj.com

Page 4 of 5 February 2006

AP503

DCS-band 4W HBT Amplifier Module

Product Information

The Communications Edge

TM

MTTF Calculation

The MTTF of the AP503 can be calculated by first

determining how much power is being dissipated by the

amplifier module. Because the device’s intended application

is to be a power amplifier pre-driver or final stage output

amplifier, the output RF power of the amplifier will help

lower the overall power dissipation.

In addition, the

amplifier can be biased with different quiescent currents, so

the calculation of the MTTF is custom to each application.

The power dissipation of the device can be calculated with

the following equation:

{The RF power is converted to Watts}

While the maximum recommended case temperature on the

datasheet is listed at 85 ˚C, it is suggested that customers

maintain an MTTF above 1 million hours.

This would

convert to a derating curve for maximum case temperature vs.

power dissipation as shown in the plot below.

Maximum Recommended Case Temperature vs. Power Dissipation

to maintain 1 million hours MTTF

50

60

70

80

90

4567

89

10

11

12

Power Dissipation (Watts)

To calculate the MTTF for the module, the junction

temperature needs to be determined. This can be easily

calculated with the module’s power dissipation, the thermal

resistance value, and the case temperature of operation:

From a numerical standpoint, the MTTF can be calculated

using the Arrhenius equation:

MTTF = A* e

(Ea/k/Tj)

A = Pre-exponential Factor = 6.087 x 10

Ea = Activation Energy = 1.39 eV

k = Boltzmann’s Constant = 8.617 x 10

A graphical view of the MTTF can be shown in the plot

below.

MTTF vs. Junction Temperature

1.E+05

1.E+06

1.E+07

130

140

150

160

170

180

Junction Temperature (°C)