I want to ask a query regarding the performance of NXP LDMOS Power Transistor part No. mmrf1312H. I am facing the reliability issue of the said device. I successfully achieved the desired parameters from the device which are stated below as:
RF Output Power Level (peak) = 60dBm (1000W)
Gain = 16.5 dB
Operating parameters are given below:
(supply was providing +30V, DC-DC converter was used to get +50V)
Quiescent current =100mA (VGS=1.94V)
Pulse Width = 256usec
Duty Cycle= 10%
Operating Temperature = 25 degree centigrade
After successfully achieved the desired parameters, i turned the device on for longer span to check the reliability of the device, but after 40 minutes suddenly the device output power drops to 200W, i turned off the power supply and did check the device via DMM. The gate terminal of the device showed short circuit.
Again i performed the test by installing the new device into the circuit. it successfully produced an output power of around 1000W but after 70 mins, it got damaged too.
I tested 8 devices, all of them got damaged gradually. Some devices were moderately failed and some were completely failed. Their life time span was 40mins, 70mins, 200mins, 30mins, 50mins, 120mins, 80mins, 20mins respectively.
Please note that the following mentioned precautions were taken while performing the test.
RF Input Power level was under 20W as provided in the datasheet.
Isolator was inserted at the output line of transistor to protect the device from high VSWR.
Heat sink temperature was continuously monitored, it was around 45 degree at the time when device got damaged.
I am so confused, what could be the reason, please help me, i shall be very thankful to you