I am trying to study a MOSFET for a space application. One of the things I have to do is study the derating analysis for a MOSFET. I am refering the document obtained from ESA site – ESA site link.
I am also attaching a screen shot below that has the derating parameter info.
The parameters are Vgs,Vds,Ids,…etc.
I understand the parameters. But what do I derate it with ?
The MOSFET under consideration- Mosfet under consideration
Let me explain my understanding –
My desired/required Vds – 5V.
The Vds of the said MOSFET is 60V. Now, 80% of that is 48V. So, this one is apt.
Supposing, I selected a MOSFET with Vds of 5, then after the 80% rule application the value is 4. This other MOSFET is not apt.
Is my analysis correct ?
Also, the last page of the datasheet shows the SEE curve.
How do I analyse that ?
Why is the gate bias negative? It is an N Channel MOSFET.
In page 1 there are 2 specifications viz – ABSOLUTE MAXIMUM RATINGS and PRE-IRRADIATION ELECTRICAL CHARACTERISTICS. Whats is the value I should be looking at? And what is the difference between the 2 please ?
Finally, it states –
Note: (1) Derated Linearly by 1.2 W/°C for TC > +25°C.
Also, is the 150W valid at 25degree celcius ?
How, do I decipher that ? For eg at 50degrees Celcius ?
What I understand is that the slope of the derating(wattage) is 1.2.
This implies that 1.2 =(150-x)/(25-50).
Hence x = 180????? Thats not possible.
Best Answer
The rated values (voltage, temp etc) are the values at which the life of component has been tested. If you want to increase the life of electronic component then you should use it below its rated values. For eg in your case, your required VDS=5V. So, check the rated VDS in datasheet which is 60V. According to datasheet for safe use of MOSFET you should apply VDS = 80 % of rated value of VDS = 0.8 X 60 = 48 V. So any system where required VDS = 48 V, this MOSFET can be reliably used. that's how you check if any component fulfills your requirement or not.
The pre-irradiation electrical characteristic and the curve is related to space radiation test. I think following link could be useful to you http://www.microsemi.com/document-portal/doc_view/123629-high-reliability-radiation-hardened-semiconductors