Unexpected VDS Protection Trigger with STDRIVE101 + STL110N10F7

[Christophe65]

Hello everyone,

I'm working on a BLDC motor project that drives an overhead (tilting) door using the STDRIVE101 gate driver, configured via MC Workbench.
The power stage uses STL110N10F7 MOSFETs, and the motor supply voltage is 24V.
PWM switching frequency is set to 20 kHz.

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:collision: Issue

I'm facing unexpected triggering of the VDS (Short Circuit) protection, especially:

• Right at motor startup

• When I disable and then re-enable the VDS protection while the motor is running, the fault is immediately triggered

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:gear: Current configuration:

• VSCREF = 1.32 V → so VDSth = 1.32 V

• Digital Filter Duration = 111.11 ns

• SW Dead-time = 800 ns

• Charge Boot Capacitor = 10 ms / Duty = 0%

• PWM frequency = 20 kHz

• MOSFETs: STL110N10F7

• Startup current: around 5 A

• DT/Mode pin is tied to GND → meaning fixed internal dead-time is selected (per datasheet)

• CP pin is also tied to GND → bootstrap auto-recharge is disabled

I also measured that the FAULT signal remains active for ~10 ms after triggering, which suggests a persistent error — not just a fast transient.

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:magnifying_glass_tilted_left: Things I've analyzed:

1. The mechanical load is significant (large door), so startup torque is high.

2. The 800 ns fixed dead-time might be too short for these MOSFETs → possible shoot-through?

3. VDS faults are more frequent at 8 kHz than at 16 kHz or higher.

4. Simply re-enabling VDS protection while running causes an immediate fault, even if the motor is spinning smoothly.

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:question_mark:Questions:

• Is the 800 ns fixed dead-time sufficient for the STL110N10F7? Should I consider leaving the DT/Mode pin floating to program the dead-time?

• What would be a reasonable Digital Filter Duration to filter out harmless VDS transients?

• Is it expected behavior that re-enabling VDS protection while running triggers a fault? Is there a recommended blanking or reset method for this?

• Would it make sense to increase VSCREF slightly to raise VDSth and tolerate short transients better?

• Any recommendation for optimal PWM frequency with this kind of load and protection enabled?

Thanks in advance for any insights or suggestions!

[Dario CUCCHI]

Hello @Christophe65 ,

Based on your schematic, I can say that 800 ns are more than enough. I can suggest to decrease it down to 500 ns if you are using a PWM frequency at 20 kHz. I’m also assuming, based on your description that you have removed the 51 kOhm resistor and connected the DT/MODE pin directly to GND. If my assumption is wrong, please let me know. Then, the DT/MODE pin cannot be left unconnected: it is not a valid configuration.

From the schematic I also see that there is no capacitor on REG12 pin. This could be a possible cause of the FAULT triggering. You must connect a capacitor as near as possible to the STDRIVE101 pins (which are REG12 and the GND): a 4.7 uF or higher should be ok.

You can do the test using the same values of VSCREF and PWM frequency you selected, so 1.32 V and 20 kHz.

Let me know if it works.

[Christophe65]

Subject: REG12 Instability and VDS Fault Improvements

Hello,

I’ve added a 4.7 µF electrolytic capacitor to the REG12 pin (ceramic capacitor is on its way and will be replaced tomorrow). This already brings an improvement: when I disable the VDS protection (by pulling SCREF to 3.3 V), the motor starts correctly. When I re-enable the protection afterward, the motor no longer stops as it used to — so things are getting better.

I also monitored the REG12 voltage with an oscilloscope and noticed a voltage dip at every switching event. Additionally, the GHS1 signal appears quite noisy during commutation. I believe this instability is due to insufficient bypassing on REG12.

I expect the issue to be resolved once I replace the electrolytic capacitor with a proper 4.7 µF ceramic + an additional 100 nF ceramic capacitor, both placed close to the REG12 and GND pins.

Thanks again for your support — I’ll report back after the test.