Hello,
I have some questions about ISO7637-2 and ISO16750-2 transient pulse simulations using the basic model and the electro-thermal model of TVS diodes in LTspice.
1) In a DC sweep simulation, I observed different IV characteristic curves between the basic model and the electro-thermal model of TVS diodes.
(a) Basic model of SM4T28CAY
According to the DC sweep simulation results using the basic model, the diode current is approximately 25A at a diode voltage of 40V.
Q1) The SM4T28CAY has a clamping voltage of 38.9V at IPP of 10.3A (10/1000us). Is the resultant IV-curve of the simulation reasonable?
b) Electro-thermal model of SM4T28CAY
The results of the DC sweep simulation using the electro-thermal model are significantly different from those of the basic model.
Q2) The current is very small. Can't I use the electro-thermal model for DC sweep simulations?
Q3) Why are these results occurring?
2) In Load Dump with Suppression Test B, the current and voltage of the electro-thermal model and the basic model of TVS diodes were compared.
a) Basic model of SM4T28CAY
According to the simulation results using the basic model,
VTVS is nearly constant,
and ITVS is thought to be determined by VTVS, the diode voltage in the IV-curve.
And, actually, too much power dissipation occurs at the SM4T28CAY.
b) Electro-thermal model of SM4T28CAY
According to the simulation results using the electro-thermal model,
the section where VTVS is constant has become longer,
and it seems difficult to match the ITVS to the VTVS in the IV characteristic curve.
Q4) The ITVS initially has a large current flow. What characteristics of the TVS determine this value?
Q5) The ITVS decreases rapidly even when VTVS is constant. What is the reason for this?
Q6) Which result is closer to reality: the basic model or the electro-thermal model?
If you need more information, please let me know.
Best Regards,
BK
