ESD vs. BLDC transients

Looking at the STspin32G4 MCU + BLDC data sheet page 7, VM (motor voltage) is rated for 75v, but in the ESD section it has a DCM rating of 500v.

Is a DCM ESD event, the same as a motor transient voltage spike in the 0.2 uS order?

Order! Order !

No. The DCM is a test where there is a tiny charge between 1 and 2ns due to discharge of a 100pF / 500v capacitor. The module must survive that. If you push 500v for 0.2us (200 ns) that will most definitely kill the module — you will be pushing two orders of magnitude more power into the module.

I see, unfortunately the data sheet does not specify the actual diodes in the driver. Since the OUTx pin is subjected to the collapsing magnetic field in the coils, before it reaches any bulk capacitor. What would be the use case for these 75v (+2v for OUTx) rated MCU + Driver. @Valentine you have some experience with these small integrated devices? Does the 75v (+2v) rating signify the highest eg. 0.2uS transient on the OUTx

The 75v is the highest on the input. 78v is the highest on the output. 80v is the highest ever on transients.

Unfortunately, I believe you are correct in assuming that any transients over 80v would probably damage the driver.

The good news is that there are very good ways in dealing with transients. You can adjust the slew rate with a resistor to the gate, and place a carefully chosen snubber capacitor between the phase output and the ground. This will reasonably suppress any transients if you really decide to push the driver to 75v. The bad news is that this will complicate your design and may make it noisy (audibly noisy, like sounds) and less efficient.

In your case, if you really want to go that high, I would suggest designing something like a discrete solution with IR2136STRPBF which is rated at 600v. Problem is, that driver is rather large, and I mean, LARGE. Also, you must select correct high voltage diodes and capacitors to handle voltage over 100v, preferably 200+ volts to control the slew rate. The challenge is to select the correct components. This board below is 135v/200A guaranteed, can handle ringing transients up to 200v. Problem is, it’s 10cm x 10cm, and that’s huge

That’s a 600v driver in the middle, notice how big it is.

When you get to such high voltages, you end up trading off a lot.

That portion in the middle controls the slew rate and ringing on the way to the mosfets, and that is also really large to handle 200v.

Life is a trade-off.



10x10cm is still pretty small for a eMC running up to 200amp! 27 kW

Naturally I’m wondering if the STspin32G4 can handle a 14 cell battery (58.8v)?

It does not leave much headroom for spikes, but maybe the spike scenario is not a real issue. I think I’m overthinking the spikes and underestimating the body-diode. They do state in the data sheet, that the test conditions was 60v.