MOSFETs Q1, Q2, Q9, Q10 damaged when applying 230 VAC input with STGAP2SICS gate drivers

[Nithi]

Problem Summary

We have developed a three‑phase servo motor drive using STGAP2SICS isolated gate drivers and IPW65R190C7XKSA1 MOSFETs.

The inverter works perfectly at low DC input voltage (25–40 V DC).
However, when we apply 230 V AC (rectified ~320 V DC) and send control signals to the U, V, W inputs, MOSFETs Q1, Q2, Q9, and Q10 fail immediately, even under no‑load condition.

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Motor Specifications

• Voltage: 230 V
• Power: 2000 W
• Rated RPM: 2200
• Gearbox Ratio: 5.067:1

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Test Conditions

Parameter Low Voltage Test High Voltage Test

Input Source	25–40 V DC	230 V AC (rectified)
Output Frequency	10 Hz	36 Hz
Modulation Index	0.5	0.5
Measured Current	~2 A	7–9 A (unexpected, no load)
Dead‑time	300 ns	300 ns
Start Method	Instant Start	Ramp‑up

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Gate Driver IC Used

STGAP2SICSNTR

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Symptoms

• Only the U‑phase high‑side and low‑side MOSFETs fail (Q1, Q2).
• Same issue happens in the W‑phase (Q9, Q10).
• MOSFETs fail instantly as soon as the PWM is applied at high‑voltage input.
• No load connected to the motor during testing.

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Attachments

• Full schematic PDF
• Firmware settings (PWM configuration, dead‑time, carrier frequency, etc.)

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Request for Help

We would like help in diagnosing why MOSFETs fail only at high voltage.
Specific guidance needed on:

1. STGAP2SICS gate driver configuration

   • Proper BOOT strap design
   • Recommended gate resistors (turn‑ON / turn‑OFF)
   • DESAT protection setup
   • Miller clamp usage

2. PCB layout concerns

   • Gate loop inductance
   • Power ground vs isolated ground separation
   • High‑side switching node dv/dt handling

3. Firmware‑related issues

   • PWM edges
   • Dead‑time sufficiency at high voltage
   • Shoot‑through analysis

4. Whether the unexpectedly high 7–9 A no‑load current indicates:

   • Incorrect switching sequence
   • MOSFET cross‑conduction
   • dv/dt‑induced gate turn‑ON
   • Faulty bootstrap supply design

Any insights from ST engineers or community experts will be greatly appreciated.

Thank you!

[Peter BENSCH]

Welcome @Nithi, to the community!

Is there a specific reason why you are using a driver for SiC MOSFETs for Si MOSFETs?

Perhaps you should consider the p2p replacement STGAP2HS instead?

Regards
/Peter

[AScha.3]

>STGAP2SICS gate driver configuration

1. I hope you have no 0,1u there !  NO cap here.

2. gate resistors: i would start with value from ds : 10 + 10 ohm 

3. remove D1 . (what should it do useful ?? )

4. with new mosfet ... :)  , no HV power supply + load : check with dual channel scope the gate signals !

looks like this:

(for this test connect scope probes + ground to hi+lo gate + source ; without any supply on HV !!!)

IF they look fine, remove probes,  try with HV (30V or so) ; if good , = almost zero supply current , apply some load.

IF all fine, try with full HV .