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LM61495-Q1: thermal issue under 85C ambient temperature

Elec Cheng
Expert 7055 points
Part Number: LM61495-Q1

Hi Expert,

Recently our customer evaluates our LM61495-Q1 and find there might be some thermal issue. When operating 5V/10A output, the efficiency is around 90%. So the total power loss is about 5.55W. Considering below thermal parameters, the total temp rising is about 110C, which is really high. The customer's working temp is 85C. It seems that this device's working temp is very narrow. I don't know if my calculation is wrong. Could you please kindly help clarify? Thanks.

BR,

Elec Cheng

  • 0
    TI__Guru 50120 points

    Hello Elec,

    1. Is the customer using the default LM61495EVM to evaluate the part's thermal behavior? 
      1. If so, how is the customer measuring efficiency in their test setup? It is suggested to have voltage DMM connection at VIN and VOUT sense test points.  
    2. What is the VIN and FSW application condition?

    The value that is highlight (21.6C/W) is based off of the thermal performance image at room for VIN = 12V, VOUT = 5V, FSW = 400kHz, IOUT = 10A shown in Figure 6-16 of the User's Guide. 

    Datasheet efficiency curve (based off EVM data) for VIN = 13.5V (close to 12V), VOUT = 5V, FSW = 400kHz IOUT = 10A, shows efficiency of ~93%. 

    Even at VIN = 24V, the efficiency curve shows around 92.5%. 

    93% efficiency for a 50W output power condition would equate to a power loss of ~3.76W. 

    Regards,
    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Expert 7055 points

    Hi Jimmy,

    Thanks for your help. I already talk with Andy and he tells that lower switching frequency will help. Thanks.

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Guru 50120 points

    Hi Elec,

    Thanks for the update. Lower frequency will result in higher efficiency and lower power dissipation. This in term will result in a cooler part.

    Regards,

    Jimmy