The nonlinear compact thermal model of power MOS transistors

1
The nonlinear compact thermal model of power MOS
transistors

• Krzysztof Górecki and Janusz Zarebski
• Department of Marine Electronics
• Gdynia Maritime University, POLAND

2
Outline

• Introduction
• The thermal model form
• Estimation of the model parameters
• Verification of the model accuracy
• Conclusions

3
Introduction

• Three phenomena responsible for abstraction of
  the heat dissipated in semiconductor devices
  conduction, convection and radiation
• The efficiency of these mechanisms depend on the
  device inner temperature Tj, the case temperature
  TC and the ambient temperature Ta.
• In modeling of the device cooling the compact
  thermal model is used.
• The compact thermal models describe the
  difference Tj - Ta as a function of the thermal
  power pth dissipated in the device. In this model
  the transient thermal impedance Z(t) or the
  thermal resistance Rth of the device exists.
• The network representations of the device thermal
  model

4
Introduction (cont.)

• Both the network are fully equivalent from the
  point of view of the terminal Tj, but
• the Foster network has no direct physical
  interpretation,
• the Cauer network results directly from
  dyscretization of the one-dimensional heat
  transfer equation.
• The compact thermal models presented in the
  literature are linear models - influence of the
  device inner temperature on the efficiency of the
  heat abstraction is not included in these models.
• From measurements Z(t) f(pth) and Rth f(pth)
• The nonlinear thermal model is needed.

5
The model form

• The network form of the nonlinear compact thermal
  model
• In order to obtain the nonlinear compact thermal
  model, five following stages have to be
  performed
• the device Z(t) in the wide range of pth should
  be measured.
• the values of the elements Ri,Ci (Cauer network)
  are estimated with the use of the algorithm ESTYM
  at various values of the power.
• the dependence Ri(pth) and Ci(pth) are drafted.
  Then, on the basis of these dependences, the
  proper approximation function is fitted.
• the values of the parameters existing in the
  dependences Ci(pth) and Ri(pth) are estimated.
• the proper model of the network form is
  formulated and implemented to SPICE.

6
Estimation of the model parameters

• The described algorithm is illustrated on the
  example of the uncapsulated transistor MTD20N06V
  operating without any heat-sink at Ta 20oC.
• The courses of Z(t) at pth in the range from 0.05
  W to 1.2 W are measured. The measured Tj has
  values from 28oC to 150oC.
• The dependences Ri(pth) and Ci(pth) are obtained
  with the use of the algorithm ESTYM.

7
Estimation of the model parameters

• the following description of the dependence
  Ci(pth) and Ri(pth) is proposed
• where Ci0, ai1, ai2, bi1, bi2, di1, di2, ei1,
  ei2, Ri0, pi1, pi2, pi3, pi4 are the model
  parameters of the values

8
Verification of the model accuracy

• P0 Pm 0.5 W
• f 0.01 Hz

Nonlinear thermal model
Linear thermal model for high power
Linear thermal model for small power
9
Verification of the model accuracy (cont.)
10
Conclusions

• In the paper the compact nonlinear thermal model
  of a semiconductor device is proposed.
• The accuracy of this model is verified on the
  example of the power MOS transistor MTD20N06V.
• A good agreement between the measurements and the
  calculations in the wide range of changes of the
  device dissipated power and for various cooling
  conditions is achieved.
• The examples show a strong influence of the power
  dissipated in the device on the values of its
  thermal parameters the thermal resistance and
  the transient thermal impedance.
• For the device operating without a heat-sink, the
  changes of thermal resistance corresponding to
  the considered changes of the power equal to even
  50 are observed. So, omitting nonlinearities in
  the device thermal model can leads to serious
  errors in the calculations of the device inner
  temperature.
• The proposed nonlinear thermal model can be used
  in the construction of the electrothermal model
  of the power MOS transistors, dedicated to the
  analyze and design electronic circuits.

11
Thank you for your attention