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MOSFET (Si/SiC) Forum Discussions

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What is the Avalanche capability of CoolMOS devices?
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yiye_4841451
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Moderator 5 replies posted Welcome! First reply posted
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The maximum allowed energy that can be dissipated in the device during a single avalanche operation (i.e. during turn off of an unclamped inductive load) at IAR and at a starting temperature of 25°C. Some manufacturers refer to EAS as the energy resulting in the maximum allowed junction temperature. (For CoolMOS™ however, EAS is not back-calculated from TJ,max but rather determined from characterization results together with simulation results.)

2596.attach
An avalanche test can be carried out on a simple unclamped inductive load switching circuit as shown in this figure. A voltage pulse is applied to the gate to turn the MOSFET on and allow the load current to ramp up according to the inductor L and the drain supply voltage VDD. When the Mosfet is turned off, the current in the inductor continues to flow and causes the voltage across the MOSFET to rise sharply. The resulting over-voltage is clamped at the breakdown voltage VBR and remains at VBR until the load current reaches zero. Breakdown happens once the critical electric field is reached at some point in the device. The breakdown mechanism itself is not destructive for a MOSFET but heat caused by the large breakdown current can be destructive. Hence, the limiting factor for the maximum allowed EAS is the maximum temperature resulting from an avalanche event.

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1 Reply
yiye_4841451
Moderator
Moderator 5 replies posted Welcome! First reply posted
Moderator
The maximum allowed energy that can be dissipated in the device during a single avalanche operation (i.e. during turn off of an unclamped inductive load) at IAR and at a starting temperature of 25°C. Some manufacturers refer to EAS as the energy resulting in the maximum allowed junction temperature. (For CoolMOS™ however, EAS is not back-calculated from TJ,max but rather determined from characterization results together with simulation results.)

2596.attach
An avalanche test can be carried out on a simple unclamped inductive load switching circuit as shown in this figure. A voltage pulse is applied to the gate to turn the MOSFET on and allow the load current to ramp up according to the inductor L and the drain supply voltage VDD. When the Mosfet is turned off, the current in the inductor continues to flow and causes the voltage across the MOSFET to rise sharply. The resulting over-voltage is clamped at the breakdown voltage VBR and remains at VBR until the load current reaches zero. Breakdown happens once the critical electric field is reached at some point in the device. The breakdown mechanism itself is not destructive for a MOSFET but heat caused by the large breakdown current can be destructive. Hence, the limiting factor for the maximum allowed EAS is the maximum temperature resulting from an avalanche event.
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