UCC27624: Introduce delay on gate driver output

Hi Rubas,

Thanks for your answer. So I added a stronger filter for the gate like this:

I calculated the rise time based on the low pass filter rise time (R=10k, C=2.2uF) and neglected a bit

the turn on time of the mosfet because it is relative small respect to that ~50ms. What do you think?

Thanks,

Andras

Hi Andras,

it is a holiday in the US this week, so responses will be delayed. Our team will get back to you early next week.

Regards,

Daniel

Hi Andras,

Thank you for your patience. Is it possible you can share the full schematic and system characteristics (VDD, input dv/dt, and switching frequency)? While you could theoretically have a long rise/fall time, it's not advisable to have it too long as it could cause switching losses and damage the power device. I see you explained the reasoning in your original post, but can you go into more details on why you need such a long rise/fall time?

Thanks,
Rubas

Hi Andras,

Just following up to see if you need any more help.

Thanks,
Rubas

Hi Rubas,

Sorry for the delay.

The same problem came into my mind regarding the power loss/uncertain state.

I think yes, it is much better to put the RC filter in front of the gate driver like this below in the picture. Do you agree?
Please see the INA part which is the delayed line:

Thanks,

Andras

I forgot to mention that the CONT_LOW_ISO_DRV signal comes from a ISO7760 TI's digital isolator's output.

Regards,

Andras

Hi Rubas,

Thanks, I understand.

So for around 50ms delay what resistor do you recommend for the following mosfet:

https://www.onsemi.com/download/data-sheet/pdf/ncv8406-d.pdf

The problem is that I do not see total gate charge value for this mosfet only rise time but I checked a similar mosfet

which has 15nC total gate charge (Qg) / 900pF and around 1.5Ohm gate resistance.

So if I use the formula RC time constant with R=10MOhm, Cg=900pF and normally 4RC is sufficient for the gate to be activated

then 4RC = 4 * 10MOhm * 900pF = 36ms only which is still not 50ms and and we are at 10MOhm.

Do you think it is realistic or I make some mistake?

Thanks,
Andras

Yes I forgot to answer why I need long rise time:
So we drive high voltage/current contactors with these drivers/mostfet and we want to shift the turn on of different contactors to reduce lots of inrush current for the contactor's coil.

Hi,

As you said I find it quite risky too to put RC on the gate so I guess I will put that in front of the gate driver and let the isolator that drives the input to charge up the input of the gate driver.

Thanks,

Andras