1

I'm reading through a white paper titled Estimating MOSFET Parameters from the Data Sheet (PDF), published by Texas Instruments in 2002, and in section "A3. Gate threshold and Miller plateau voltages", the equation at the top of page 2-43 contains a magic number "-0.007 V/°C" for the temperature coefficient (TC). I'm wondering if anyone knows where this value comes from, or perhaps knows the method that was used to arrive at this value. (NB: The MOSFET that's being used for the example is IRFP450; see the first paragraph on page 2-40.)

Jim Fischer
  • 2,984
  • 11
  • 14
  • 4
    Completely a guess: interpolation between the two curves shown on the datasheet? – Hearth Sep 16 '20 at 14:05
  • https://www.stmicroelectronics.com.cn/resource/en/application_note/cd00115755-how-to-achieve-the-threshold-voltage-thermal-coefficient-of-the-mosfet-acting-on-design-parameters-stmicroelectronics.pdf includes a derivation in a number of equations; unfortunately I don't have the time right now to reproduce the relevant ones with the level of commentary that I think a high-quality answer deserves, and I also don't have enough details on the "typical" TI MOSFET to apply these equations and verify whether they yield -0.007 V/degC or thereabout. – nanofarad Sep 16 '20 at 14:48
  • 1
    It's Finagle's constant... – Solar Mike Sep 16 '20 at 19:37
  • I'm sure it's empirical. The derivation from physics would be **hard**. (Developing the fuller shape of the Fermi surface, its influence on the screening properties of electrons, the electron screening interactions with phonon wavevector potentials, localized magnetic moments interactions with the electron screening, oscillatory exchange coupling, topological transitions, and I don't know what else. Someone may have done it. But you'd need to find a Fermiologist of some sort to point you in the right direction.) – jonk Sep 16 '20 at 19:41
  • @Hearth, I think your guess is correct. When I use interpolation to estimate a value for the temperature coefficient (TC) via the 150°C and 25°C curves shown on the "Typical Transfer Characteristics" figure on pg. 2-42, I get TC=0.008 V/°C. Thanks... – Jim Fischer Sep 17 '20 at 08:02

0 Answers0