Double pulse test

Emma

20240605 - 副本.zip

hello
I have encountered difficulties in calculating the loss of dual pulse test with PSpice. I need your help for two problems.
This is my circuit diagram, attachment 1 is my simulation file.

I calculated the loss according to the conditions on the datasheet (as shown in the figure 1 below). The voltage I measured was 2-pin (MID) and 3-pin (V-), and the current I measured was 3-pin (V-), simulating the situation when the load current I measured was 900A(as shown in the figure 2 below)

Question 1: When I set V1 of V5 to -4V, the simulation results have been stagnant(as shown in the figure below), but when I set it to -3.9999V, it works normally.

Question 2: The turn-off voltage measured by me is 18.665mJ(I calculated according to the calculation requirements on the datasheet and using the S-function), but the turn-off voltage of the Datasheet under the same conditions is obviously greater than 20mJ(as shown in the figure below), and all of my conditions are the same as that of the Datasheet. Why is there such a significant difference? What adjustments do I need to make if I want my simulation results to be the same as on the Datasheet?

I am very confused about these questions, and the answers to these two points are also very important to me. Thank you for reading such a long letter, and I am looking forward to your reply, thank you!

Forum_Moderator

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Bdeboi

Hi Emma,

Question 1

This is interesting. I have not run into this issue. I'll investigate it, but in the meantime, I would just use your workaround.

Question 2

So first - this kind of matching is actually not that bad. The SPICE model is fit across bus voltage, load current, gate resistance, and temperature, and must consider slew rates/timings/switching energies. When looking at a single characteristic at a single condition, a 10%-20% deviation is not surprising.

However, for your simulation there is a simple solution. Gate drivers intrinsically have some resistance within them. For this module, refer to the CGD1700HB3P-HM3 module that was used to measure the CAS480M12HM3 power module for the datasheet.

https://assets.wolfspeed.com/uploads/2024/01/Wolfspeed_CGD1700HB3P-HM3_data_sheet.pdf

You'll see that this gate driver has an internal RGON of 0.4 Ω and an internal RGOFF of 0.3 Ω. You should include these in your simulation. You can probably just average these and add 0.35 Ω to your RGEXT, but if you want to split out on/off resistances consider the below circuit as an example of how to do this.

Also, I would add the gate resistance to the inactive switch. During our datasheet testing, the gate resistance is on both the high-side and low-side switches during operation.

Let me know if you have any further questions,

Brian

Emma

Thank you for your answer, but I still have some questions about the simulation, I have modified the simulation according to your answer, the specific simulation program is shown in the attachment, but the turn-off loss obtained through the simulation is 26.932mJ, the turn-on loss is 23.875mJ, and the datasheet data is still very different, I would like to ask what is the problem?

20241120halfbridgeCAS480.zip

Looking forward to your reply. Thank you very much

Bdeboi

Hello,

Comparing your simulated losses (~51 mJ) to the datasheet (~56 mJ), this is very reasonable. Remember - the SPICE models take the static characteristics of the device (Rdson, capacitances) and predicts how the device will switch in your circuit (the circuit itself has its own parasitics, the gate driver has its own behavior, etc.)

All this to say - this kind of matching of dynamic behavior is actually very good. If you are looking for perfect datasheet matching, I recommend using our PLECS models instead of predictive SPICE models. If you are looking to perfectly match the datasheet for a particular condition, feel free to further tune Rgon/Rgoff.

Thanks,

Brian

BlakeNelson

I hope that this answered your question. I will close this discussion for now but if you have a follow up question, please "Start a New Discussion" and we would be glad to support you further.

Blake