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LM2936: Lm2936 heat problem

Ihab Alsheikh
Intellectual 255 points
Part Number: LM2936

Hi TI Expert 

I have an over heat problem in LM2936MP-5.0 When the external power is 30 V.

The load current is below 30 mA.

Regards

Ihab

  • 0
    TI__Mastermind 23361 points

    Hi Ihab, 

    What's the output voltage of the LDO and in what package? When you say heat problem, did the regulator hit thermal shutdown? 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Intellectual 255 points

    Hi Jason
    The output is 5V in package LM2936MP-5.0_NOPB ( SOT-223).
    the heat problem by hand touching Slight smile , It is too hot that you can't touch it, 
    We should consider that there is a packaging stage and it will be hotter

    Regards,

    Ihab Alsheikh

  • +1 in reply to Ihab Alsheikh
    TI__Mastermind 23361 points

    Hi Ihab, 

    The LDO has a recommended junction temperature of up to 125C. I would not recommend using your finger to sense the temperature. Instead, please use a thermal gun or estimate the temperature by using  (Vin-Vout)xLoadx Rja, the Rja for SOT-223 is 59.6C/W. 

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    Intellectual 255 points

    Hi Jason,

    Thank you for your replay.

    Jason Song said:
    (Vin-Vout)xLoadx Rj

    (Vin = 30 V, Vout = 5V , Load = 30 mA)

    that means the estimated temperature of LM2936 is 44.7.
    adding the ambient temperature (40 C) which means 84.7 C. am I right? 

    The board which I used will work all the day, Could I face a problem because of regulator heat ?

    Regards,
    Ihab

  • +1 in reply to Ihab Alsheikh
    TI__Mastermind 23361 points

    Hi Ihab, 

    Yes, your calculation is correct. The LDO is designed to operate under 125C and you are good. 

    Regards, 
    Jason Song