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Intrinsic Gate resistance of FQP9N90C MOSFET?

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ocset:
actually the method of post #3 does not seem to work with the IPP90R1K2C3 FET.

The stated RG (admittedly at 1MHz) is 1.3 Ohms................but the method of #3 above gives it as 25 Ohms.

IPP90R1K2CE FET
https://www.infineon.com/dgdl/Infineon-IPP90R1K2C3-DS-v01_00-en.pdf?fileId=db3a30432313ff5e0123a89fe8085c04

The IPP90R1K2C3 FET has an RG figure of 1.3 Ohms, but then in the "conditions" column of page 3 it syas "RG = 81.3 Ohms".

What we wish to do is find RG as part of our setting of our external series gate resistance..................we will of course carry out tests and modify in accordance, but we wish to set an initial value for the series gate resistor.
As you know, this resistor has a big impact on the switching losses.

ogden:

--- Quote from: treez on October 09, 2018, 07:20:28 am ---actually the method of post #3 does not seem to work with the IPP90R1K2C3 FET.

The stated RG (admittedly at 1MHz) is 1.3 Ohms................but the method of #3 above gives it as 25 Ohms.

--- End quote ---

Then use datasheet figure and do not calculate using post #3 method :) [edit] Most likely it is not correct. I added note in original post as well. [/edit] Obviously if you want to know Rg at patricular frequency ( @ 1MHz ) as specified in the datasheet - use LCR meter. Post #3 is simplest possible way to get ballpark value and obviously does not account for fact that Rg_internal is ESR figure.


--- Quote ---The IPP90R1K2C3 FET has an RG figure of 1.3 Ohms, but then in the "conditions" column of page 3 it syas "RG = 81.3 Ohms".

--- End quote ---

To me it looks like sum of external 80 Ohms resistor and 1.3 Ohms Rg_internal which were used for tests to get particular results.


--- Quote ---What we wish to do is find RG as part of our setting of our external series gate resistance..................we will of course carry out tests and modify in accordance, but we wish to set an initial value for the series gate resistor.
As you know, this resistor has a big impact on the switching losses.

--- End quote ---

What can I say... There's more productive way of getting information you want than forum post: google search for application notes of MOSFET manufacturers. I typed in "mosfet gate resistance considerations" and got very good document for you as first hit:

https://toshiba.semicon-storage.com/info/docget.jsp?did=59460&prodName=TK5Q65W

T3sl4co1l:
I measured this.



Sorry it's FQA (TO-3P), not FQP.

Tim

ogden:

--- Quote from: T3sl4co1l on October 09, 2018, 10:47:44 am ---I measured this.

--- End quote ---

Sub-ps time resolution, huh? :) - Impressive stuff. It is TDR instrument or pulser+scope? Could you please tell more about how, using what tools you measured and then how calculated RG_internal?

Most likely it is not how commercial(?) supplies shall be made, but I would not waste time measuring/calculating. Anyway external gate resistor will be as small as possible and my feeling tells much less than 80 Ohms. So I would start with minimum value my gate driver can switch into gate capacitance without blowing up, like <= 10 Ohms, then look - it pass or fails EMC. If pass then that's it, job is done.

T3sl4co1l:
As crude as can be, avalanche pulse generator (waveform into 50 ohms shown as Ref), BNC tee to binding posts and scope; binding posts to twisted pair up to gate.  Waveforms are interpolated from a 10GS/s acquisition (equivalent time sampled, 350MHz BW).

Note that the scope and source act in parallel, hence Rsrc = 25 ohms.

Decimals are incidental (why bother rounding down?).  The RLC network is simulated with a modest timestep because it's easily written that way (naive Newton integration), but high frequency elements are easily divergent at this scale (e.g., if C is made to be a few pF, or L1 or L2 is made similarly small), and a better integration method would be beneficial (trapezoidal, RK2..).  I don't feel like writing those out in a spreadsheet, much faster to load up another few thousand cells and run it again.

The L1-C-L2 parameters were intended to simulate the twisted pair, but it seems a best fit doesn't quite fit with those alone (i.e., the high frequency ringing isn't captured well).  I think an LC tank in series with what's shown would get closer (i.e., simulating mode conversion because twisted pair).  Anyway, that's just the tight squigglies, which it seems got averaged over pretty well on the best-fit, so that's nice.

The R value seems robust; it acts like a vertical offset to the 'rebound' phase of the waveform, and nearby values of R and C2 don't fit nearly as well as these do.

Tim

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