Communication Concepts 2M 1KW Amateur Application Note - Manual (Page 10)

10
RF Reference Design Data
Freescale Semiconductor
MRFE6VP61K25H MRFE6VP61K25HS 2 Meter Amateur
Ruggedness
MRFE6VP61K25H is a very rugged part capable of
handling 65:1 VSWR, provided thermal limits are not
exceeded.
It was designed for high mismatch applications, such as
laser and plasma exciters, that under normal operation
exhibit high VSWR values at startup and then come back to
a more friendly impedance. In CW at high VSWR values and
simultaneously at rated power, the limiting factor is the
maximum DC power dissipation.
VSWR protection that shuts down the gate voltage within
10 ms will protect the transistor effectively.
The amplifier presented here was tested at full power with
all phase angles with 10 ms pulsed 5% duty cycle without
failure or degradation in RF performance.
Reliability
MTTF is defined as the mean time to failure of 50% of the
device within a sample size, the primary factor in device
reliability failure is due to electromigration. Once average
operating condition for the applicatin is set, MTTF can be
calculated using the R
th
found on the offical Freescale data
sheet.
Example: If desired operating output power is 1000 W, with
82% drain efficiency at 43 volts.
• I
Drain
@ 1 kW 82% eff = 28.2 A
• MRFE6VP61K25H R
th
= 0.15°C/W, case temperature =
63°C
• Dissipated power = 219 Watts
• Temperature rise (junction to case) = 219 Watts ×
0.15°C/W = 32.8°C
• T J
= T
rise
+ T
case
= 63°C + 32.8°C = 95.8°C
Utilizing the graph below which cacluates MTTF versus
I
Drain
and T
J;
I
Drain
= 28 A, MTTF for this example was 8000
years.
230
100000
70
1000
100
1
90 110 130 150 170
MTTF
(YEAR
S)
190 210
10000
10
24 Amp
28 Amp
20 Amp
Figure 13. MTTF versus Junction Temperature
T
J
, JUNCTION TEMPERATURE (°C)
There is an MTTF (Median--Time--To--Failure) calculator (3)
available to assist the customers in estimating the
MRFE6VP61K25H
device reliability in terms of
electromigration wear--out mechanism.