The Communications Edge TM
AP512
UMTS-band 8W HBT Amplifier Module
Product Information
MTTF Calculation
The MTTF of the AP512 can be calculated by first To calculate the MTTF for the module, the junction
determining how much power is being dissipated by the temperature needs to be determined. This can be easily
amplifier module. Because the device’s intended application calculated with the module’s power dissipation, the thermal
is to be a power amplifier pre-driver or final stage output resistance value, and the case temperature of operation:
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.
Tj = Pdiss * Rth + Tcase
Tj = Junction temperature
P
diss = Power dissipation (calculated from above)
Rth = Thermal resistance = 4.5 ˚C/W
Tcase = Case temperature of module’s heat sink
The power dissipation of the device can be calculated with
the following equation:
From a numerical standpoint, the MTTF can be calculated
using the Arrhenius equation:
P
diss = Vcc * Icc – (Output RF Power – Input RF Power),
Vcc = Operating supply voltage = 12V
Icc = Operating current
MTTF = A* e(Ea/k/Tj)
A = Pre-exponential Factor = 6.087 x 10-11 hours
Ea = Activation Energy = 1.39 eV
{The RF power is converted to Watts}
k = Boltzmann’s Constant = 8.617 x 10-5 eV/ ºK
Tj = Junction Temperature (ºK) = Tj (ºC) + 273
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.
A graphical view of the MTTF can be shown in the plot
below.
MTTF vs. Junction Temperature
Maximum Recommended Case Temperature vs. Power Dissipation
1.E+07
to maintain 1 million hours MTTF
90
80
70
60
50
1.E+06
1.E+05
130
140
150
160
170
180
Junction Temperature (°C)
8
10
12
14
16
18
20
22
24
Power Dissipation (Watts)
Specifications and information are subject to change without notice
Page 4 of 5 June 2006
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