LT4363-2 Current Limit Protection( DC Power Supply)

Hello,

FET  Switch (U21)  is burned below conditions.

DC POWER  SUPPLY 12V: CURRENT LIMIT  2A,

LOAD: 2A,

WHEN  POWER ON,

FET(U21):  TPW4R50ANHQ

         surface  mount,  

Q)  How  can  I   prevent  FET  burning?

(Change   large size  FET?)

(DC POWER SUPPLY  Current Limit: 2A  to 15A)

(LOAD: 0  to 15A)

(Customer  may use DC  POWER SUPPLY  with  CURRENT LIMIT)

Thank you for your help.

I am  waiting your answer.

Regards,

Circuit Diagram (Pls  do not  open  to  a WEB)

Waveform1    U21  FET Switch is burned(or  High temp.)

 DC  SUPPLY Current  limit  :  2.5A

LOAD:2.5A

Waveform2  U21 FET  (NO PLOBLEM)

DC  SUPLLY Current limt:  2.5A

LOAD:0.5A

Parents
  • 0
    •  Analog Employees 
    on Oct 13, 2020 6:58 PM

    Hello,  In most applications, the power supply current limit is higher than the load, otherwise the power supply voltage will fall (and rise if load cuts off) and not be stable. That is why the LT4363 gate keeps turning on/off (possibly because supply voltage keeps rising and falling above UV threshold) and stressing the FET, likely raising its temperature to destruction. (The calculated UV threshold is 10.29V, not 10.8V noted on circuit.) As your second waveform shows, one solution is to keep the supply current limit higher than load current. Even if you use a bigger FET or heat sink, the FET may not die but the instability may continue forever. Another possible solution is to turn on the load current after the input supply is much higher than the UV threshold and make sure that in current limit the supply voltage doesn't fall below UV threshold.

Reply
  • 0
    •  Analog Employees 
    on Oct 13, 2020 6:58 PM

    Hello,  In most applications, the power supply current limit is higher than the load, otherwise the power supply voltage will fall (and rise if load cuts off) and not be stable. That is why the LT4363 gate keeps turning on/off (possibly because supply voltage keeps rising and falling above UV threshold) and stressing the FET, likely raising its temperature to destruction. (The calculated UV threshold is 10.29V, not 10.8V noted on circuit.) As your second waveform shows, one solution is to keep the supply current limit higher than load current. Even if you use a bigger FET or heat sink, the FET may not die but the instability may continue forever. Another possible solution is to turn on the load current after the input supply is much higher than the UV threshold and make sure that in current limit the supply voltage doesn't fall below UV threshold.

Children
  • Hello, Thank you for your reply.

    I agree ,we should use  that "the power supply current limit is higher than the load".

    But, I(we)  can not gurantee  that "Customer uses "the power supply current limit is higher than the load".

    and, we can not change  the FET,bigger(ex:TO-220) , we do not have enough area.

    So  I  ask this COMMUNITY to find  solutions.

    If  I have more questions,asking you.