Dear All,

We built a 7.5kW H-bridge converter using IAUT260N10S5N019 MOSFETs and 2ED020I12FA gate driver. H-bridge is getting powered from a 48V battery pack and is driving an RL load.

We went for this driver for miller clamp protection and short circuit protection features. We are facing two problems with this driver which are:

1. DESAT or short circuit protection is not working - RESET pin on driver is ringing during short circuit event making gate driver signals to flow again and Driver is failing during short circuit test.
2. Miller clamp circuit of the driver is failing sometimes during normal operation of the circuit.

Normal Operation:
H- bridge is currently being operated as a synchronous buck converter. Operation of H-bridge is as follows:
State 1: Left leg top mosfet and right leg bottom mosfet are turned ON to drive the current into the load.
State 2: Left leg bottom mosfet and right leg bottom mosfet are turned ON to freewheel the current in the RL load. A dead band of 1us is given to avoid shoot-through in left leg during transition between left top and left bottom mosfets.
State 3: When pulses are taken away from all the switches, left leg bottom mosfet's body diode and right leg top mosfet's body diode will conduct to give away the energy stored in inductor to the source.

The load is connected between mid points of each leg of the H-bridge. The driver is being used in boot strap circuit configuration to drive the top mosfet in left leg. Second leg top mosfet is not given gate pulse during any state of operation.


Problem 1:: Desat or short circuit protection is not working

To validate the short circuit performance of the circuit, left leg top mosfet and right leg bottom mosfet are kept continuosly ON for some duration and then a 5us ON pulse is given to the left leg bottom MOSFET to create short circuit on left leg.
DESAT protection is not activating and gate driver is failing during this event (3 times drivers failed). Diagnosis of failed drivers using impedance test shows shorted secondary supply pins. Following waveforms are taken during short circuit test.
However, no MOSFET failed during this test but during normal tests MOSFETs are failing. So, its important to have this short circuit protection working properly.

In the following figure - Blue : Bottom gate driver output pulse; Yellow: Top gate driver output pulse; Pink : Desat Pin voltage

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In the below figure - Blue : Bottom gate driver output pulse; Yellow: Top gate driver output pulse; Pink : 15V supply on secondary side

Click image for larger version

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Problem 2:: Miller clamp circuit of the driver is failing sometimes during normal operation of the circuit.

Normal operation of the converter is explained above. It is observed that drivers are failing sometimes during normal running condition of the converter.
Fault diagnosis of some of the failed drivers with impedance test has shown low impedance on miller clamp pin which indicates failure of miller clamp transistor.
We went for miller clamp to protect MOSFETs from unwanted triggering during switching events but instead driver itself is failing in such events.


We are struck with these problems to move ahead in releasing the prototype of our product. Any support in the above mentioned issues is greatly appreciated.

Thanks!
Kashyap Gundlapalli