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LM5117: IC dissipation under different load condition

Charles Zhang1
Expert 3430 points
Part Number: LM5117

Tool/software:

Hi Team,

Do you have formula/or tool to help my customer to calculate the power dissipation of IC itself based on the different loading conditions?

For example, based on the Webench estimation, IC pd will go higher when the loading goes higher(Fsw is the same for both case), this test result aligns with my actual measurement on customer's board. 

The formula in the datasheet shows the driving loss, I am not sure if Qg of MOSFET will go much higher under a heavier load.

Also, regarding the quiescent loss, not sure if Ivcc will vary with load conditions.

Need you help to provide the proper approach to estimate the IC power dissipation, thanks!

Regards,

Charles

  • 0
    TI__Guru 58391 points

    Hello Charles

    The IC temperature might be increased by increasing the load because MOSFET & Inductor temperature rises increase the ambient temperature (/PCB temperature)  of the IC.  

    The required Qg might be slightly changed by increasing the load but the amount of change is small and you can ignore it. 

    If you'd like to match your measurement with your estimation, please measure the current flowing into the VIN pin of the IC, the PCB temperature and the IC temperature together with enough soaking time ~ 20min.  

    -EL 

  • 0 in reply to EricLee
    TI__Expert 3430 points

    Hi Eric,

    If the driving loss difference between high/low loading can be ignored, what's the rationale behind the increment of IC Pd when the load goes up?

    Regards,

    Charles  

  • 0 in reply to Charles Zhang1
    TI__Guru 58391 points

    Hello Charles

    As I mentioned in the previous post, I think the IC temperature might be increased by increasing the load because MOSFET & Inductor temperature rises increase the ambient temperature which is PCB temperature of the IC.  

    -EL