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LM5069-2: MOSFET blow up when output short

BAOCHAO YIN
Prodigy 50 points

Hi,

My application is 54V/12A. I used the downloaded EXCEL tool to design the circuit. The MOSFET is STP75N75 which has a 300W Pd.  My question is the MOSFET blow up when the output is short circuit. Would there be anyone who can help me and give some suggestion? Thanks a lot. 1777.48v LM5069_Component_Calculator.xls

  • 0
    TI__Genius 13265 points

    Hello,

    300W is too high for most devices to handle for 10 msec.  Many older FETs do not have accurate SOA's - they rely on the Theta-jc measurement, and assume that if the die temp. stays below 150C, then the device is OK.  However, more modern FET data sheets will have a much "lower" SOA (the power dissipations will be less).  The degradation in the FET SOA is an artifact of what is called Thermal Instability, which many manufacturers ignored when generating the SOA.  Infineon has a nice app. note about it entitled "Linear Mode Operation and Safe Operating Diagram of Power-MOSFETs".

    For most D2Pak FETs, 75W is safe for 10 msec up to 85 deg. C ambient.

    Regards,

    Mike

  • 0 in reply to Michael Hartshorne
    Prodigy 50 points

    Thanks Mike.

    I noticed that the high power limit may cause MOSFET damage. I tried to lower it to 50W, but the circuit can not power up with full load.