Logic level FET datasheet doent tell Vgs(th) vs temperature

[cupoftea]

Hi,
We are doing Sync Buck with G15N06K NFETs. (15vout , 3Aout, 24Vin, 150khz) We have "turn-off-fast" diodes in the gates. But what is the Vgs(th) at say 100degC?......our turn off diode may not be able to get under that. Why does the datasheet not tell?
It only tells Vgs(th) at 25degC.

G15N06K

http://www.gofordsemi.com/u_file/product/635/GOFORD-G15N06K.pdf

 

[KlausST]

Hi,

It only tells Vgs(th) at 25degC.

Yes. With a variation from 1.0V to 2.5V = 1.5V
So let´s say that V_GS_TH changes with -2.mV/K (just guessed) .. then the 1.5V variation equals a temperature variation of 750K.

This means the production variation of the MOSFET dominates over the temperature drift of V_GS_th.

Klaus

 

[D.A.(Tony)Stewart]

Below max Id, it is NTC and above it is PTC, so there is a point where it is ZTC.

 

[KlausST]

Hi,

according datasheet (post#1):
V GS(th): V DS = V GS , I D = 250µA

So it´s at the lower end of drain current. --> NTC

V_GS_th varies by about -0.5V from -55°C to 150°C ... = about -2.5mV/K for the MOSFET of post#3.

Klaus

 

[D.A.(Tony)Stewart]

Don't rely on a fixed Tempco with pulsed high currents. Take the average temp rise and keep the case below 80'C at max ambient to avoid thermal runaway,

and do not conflate Vt mfg tolerances with tempco which only occupies about 20% of the specified max range for Vt over the entire temp range.

 

[danadakk]

Just a thought but generally the manufacturer has characterization data that is acquired
before production release. Thats done by product and test engineering for semiconductor
release, and datasheet finalization. This characterization is done across process variation.

Less "guessing".

Focus on product engineer, he is usually the gatekeeper.


Regards, Dana.

 

[D.A.(Tony)Stewart]

Focus on product engineer, he is usually the gatekeeper.


Regards, Dana.

and be prepared to use a translator

But volume Mfg buyers have more clout to get answers. This is why Eng's must always include buyers on Factory questions so distribution understands, they wont get orders unless Eng'g gets answers soon.

Money gets priority.

 

[dick_freebird]

If you're using the device then you ought to have a couple handy
to measure.

What's your care-about "off" current? 1mA? 1uA? Pick one for the
experiment. Tie D=G, 10V supply, series resistor that gets you the
number for drain current at 25C. Record Vgs(25C). Now hit the oven,
take Vgs(125C). The delta is your temperature drift. Apply that drift
to the low side limit for Vgs(th) and there you go. Probably not happy
as low side limit is 1V, less a FR diode VF you would need a real nice
VOL from your driver / controller.

But VT is not an on/off cliff either. What's your "off" current close-in
to the transition, need to be and how soon, to not impose undue
stress or unacceptable switching loss (as the interval of fading
conduction should be a sliver of the cycle, it will be appear as a
switching loss although it really is shoot-through, gated, not a
capacitance stealing edge energy). So maybe it's 10mA for 100ns
instead of 1uA. Is it gonna kill you? When you're talking amps of
IOUT?

You might elect to characterize that aspect - forget the extrapolated
VT of the model, where do you hit the leakage floor (Vgs@high Vds)
Vgs-wise, and how does the floor and the subthreshold root voltage
move with temperature? Neither is in your favor but if non gate
controlled leakage is burying the channel leakage, maybe you just
fuggedaboudit (and take your lumps).

 

[D.A.(Tony)Stewart]

If you use Vgs=> 2.5 Vt, it should not matter, but if only using Vgs=2Vt then they must be subthreshold or low Vt types.