2024-07-08 02:52 AM
Hello,
I use ST's STDRIVE101 in a design to drive a three-phase BLDC motor and used the reference design EVALSTDRIVE101 as a design guideline. My design has a MOSFET switching frequency of 20 kHz and a MOSFET drain-source voltage between 36 and 42 V.
I have some questions about the design’s power stage (see screenshot from the design’s documentation below) and would be very grateful for an answer. All designators mentioned are taken from the screenshot.
My questions are:
Thanks in advance for taking the time for an answer!
Regards,
mual
Solved! Go to Solution.
2024-07-08 03:07 AM - edited 2024-07-08 03:31 AM
Hi,
> R11: Is there a strong reason for choosing 33 Ohm?
No. Choose any value...but be aware : the faster you switch, the more EMI you generate, up to (maybe) self destruction of the mosfet (oscillation or shoot might happen, depends on layout, load, current, capacities and the ruggedness of the mosfet).
The higher you choose the R11 value, the more "smooth" it will switch on, but switching loss will increase also.
So its a compromise, to get good balance EMI/spike vs. switching loss.
If you think, you can do it better (with other mosfet, it might be needed to adapt), try it.
And in a half-bridge, as its here, you change the timing - maybe dead-time needs adjusted also.
Avoid any shoot - this might kill all mosfets and driver...so if you want to experiment, have some extra parts at hand. :)
>D1: This is used for faster switching off the gate
Right.
>Resistor R14: I assume this is a pull-down
Is more for safety, if driver not active (maybe at power on or disable driver), to have a "safe" voltage at the gate.
2024-07-08 03:07 AM - edited 2024-07-08 03:31 AM
Hi,
> R11: Is there a strong reason for choosing 33 Ohm?
No. Choose any value...but be aware : the faster you switch, the more EMI you generate, up to (maybe) self destruction of the mosfet (oscillation or shoot might happen, depends on layout, load, current, capacities and the ruggedness of the mosfet).
The higher you choose the R11 value, the more "smooth" it will switch on, but switching loss will increase also.
So its a compromise, to get good balance EMI/spike vs. switching loss.
If you think, you can do it better (with other mosfet, it might be needed to adapt), try it.
And in a half-bridge, as its here, you change the timing - maybe dead-time needs adjusted also.
Avoid any shoot - this might kill all mosfets and driver...so if you want to experiment, have some extra parts at hand. :)
>D1: This is used for faster switching off the gate
Right.
>Resistor R14: I assume this is a pull-down
Is more for safety, if driver not active (maybe at power on or disable driver), to have a "safe" voltage at the gate.
2024-07-15 10:10 PM
Thank you!