Double Puls Test

nugzari

Hello,

I would like to sweep different internal component sizes. Unfortunately it doesn't work with the Spice Directive. For example, if I sweep an Rgi there is only one curve even though according to the annotation step the component takes on different values.

But if I Ctrl+Right click on the component and enter different values ​​of Rgi there then I get different courses of I(Rlow) current.

for example in this picture Rgi=2 Ohm

Rgi=10 Ohm

In this case the current has two different values ​​at the beginning of the second pulse, why?

I would like to use the Spice directive as it is much easier to see different values ​​at a glance. Can you please tell me what I'm doing wrong?

The same also applies to internal sizes such as Cag, Cug Clg or Cds, Cgd and Cgs.

I also liked to know what the difference is between G_Cgs and cgs.

Thanks in advance

Forum_Moderator

Thank you for your post, it has been approved and we will respond as soon as possible.

Bdeboi

Hello,

The reason for the difference in the operating pulse is that the difference in gate resistance causes a change in the turn off/turn on delay for the device. This causes some mismatch in the timing for different DPT states, which can result in subtle changes in the operating current.

In the below waveforms, green is Rgi=2 and blue is Rgi=10. The top waveform is for the load current through the inductor, and the bottom waveform is the current through Rlow. We see that the Rgi=2 waveform turns off earlier, and thus has a shorter charge pulse and reaches a lower current. However, at turn-on, the devices turns on sooner and begins the second charge state earlier, but at a lower current. This same behavior is observed in empirical testing and is expected.

For your sweeps, let me provide the most useful parameters:

Rgi - When specified, manually sets the internal gate resistance to this value

Vths - Threshold voltage shift that adds a voltage offset to the gate. So, Vths=2 → the device will turn on 2V sooner

Rdss - On-state resistance offset. The value of this parameter will be added to the resistance of the channel.

AFm - Number of devices in parallel. Will scale the on-state resistance, third-quadrant conduction, reverse recovery, device capacitances, internal gate resistance, and Cauer network parameters. The default value for this parameter in the CAB425M12XM3 module is 5.

ags - Scalar multiplier of the gate-source capacitance

ads - Scalar multiplier of the drain-source capacitance

agd - Scalar multiplier of the gate-drain capacitance

CgdOffset - Added offset to the gate-drain capacitance

In the .lib file, you can look for the .SUBCKT CAB425M12XM3 definition and find the default values for all of these parameters in the .param definition.

Finally, 'Cgs' is just the definition of the gate-source capacitance values (defined in nF), while 'G_Cgs' is the actual behavioral current source implemented in the circuit.

Please let me know if you have any further questions.

Thank you,

Brian

nugzari

Thanks for your answer.
I'm now trying to plot ILoad and I(Rlow). namely with Rgi 2 ohms and 10 ohms. But I don't see the difference like you do in the picture.

The directive is .step param Rgi list 2 10.

Thanks.

Bdeboi

Hello,

Right-click the module symbol to access the SpiceLine, and make sure that you are defining Rgi there as well with "Rgi = {Rgi}". See the below image. If you've done this and it is still not working, I will send you my simulation.

Thank you

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