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TPS5410D junction temperature calculation and heat sink requrements

Sesha giri
Prodigy 30 points

Other Parts Discussed in Thread: TPS54040, TPS5420

Hi ,

this is seshagiri. first started with TPS54040 for 5v@0.5A  and then moved to TPS5410D for 5v@1A. i started thermal calculations, i approached like this , please let me know my approach is correct?.

Ambient temp=70degC

for junction temperature calculation purpose i used the formula, Tj = TA +(PD*Rth)

as per TPS5410D data sheet Rth = 75 degC/Watt

PD = 5V*0.25A= 1.25W    ........ it can withstand upto 5W

as per data sheet it can with stand upto  junction temperature 125degC

but as per my calculation  Tj=TA+(PD*Rth) = 70 +(1.25*75) = 163.5degC

in this case itis crossing the recommended junction temperature 125degC, but i am using only 1.25W , but it can withstand upto 5W.

please let me know shall i need heat sink for this application.

I awaiting for anyone reply

Thank you very much in advance.

  • 0
    TI__Intellectual 2510 points

    Dear Seshagiri,

    We have to distinguish between the IC power and the one delivered to the load.

    The junction temperature is estimated by using

    IC_Tj = (IC_Pd*IC_ThetaJA) + TA

    where  IC_Pd = M_Pswitching + M_Pbody + M1.Pconduction + Vin * IC_Iq + M2.Pconduction

    This is switching device and we have to consider duty cycle, the switching frequency, rds of both internal FETs and so on.

    Best Regards,

    Flora

  • 0 in reply to Flora Carreto
    Prodigy 30 points

    Hi ,

    Thanks for the information , i saw this equation in the tps5410D data sheet and EVM document. May i know how to calculate for IC power  and one delivered to the load.

    i am using the TPS5410D in two different products, one product is consuming 250mA and another one is consuming 500mA

    Please suggest me if heat sink is required in these products. if heat sink is required please suggest the formulas..

    Awaiting for the reply

    Thanks in advance

    Best Regards

    Seshagiri

  • 0 in reply to Sesha giri
    TI__Genius 14455 points

    Hi SeshaGiri,

          The output power delivered to the load is Vout * Iout. so if your output voltage is 3.3V and output current is 500mA, then the output power is 1.65Watts.

    The IC power dissipated is the sum of the power dissipated from individual factors like internal MOSFET switching losses, MOSFET conduction losses, body diode losses, IC quiescent current losses etc.

     IC_Pd = M_Pswitching + M_Pbody + M1.Pconduction + (Vin * IC_Iq)  + M2. Pconduction(if device has low side FET)

    You can look at the Operating Values table in WEBENCH that summarizes the total IC power dissipation loss as IC_Pd.  While calculating the junction temperature of the chip, you need to use the IC_Pd and not the output power and you can see this result in the WEBENCH Operating Values table as well.

    Tj = Ta + (IC_Pd * ThetaJA).

    The TPS5420 is available in an 8 pin SOIC package and it does not support a heat sink.

    Regards,

    Gerold

     

     

  • 0
    Prodigy 30 points
    Hi,

    Thank you very much. I got the answer. TPS5140D also 8 pin SOIC. This also does not support heat sink.

    Best Regards
    Seshagiri

    On Wed, Jan 23, 2013 at 4:57 AM, Gerold Dhanabalan - WEBENCH Design Center <bounce-1132529@e2e.ti.com> wrote:

    Hi SeshaGiri,

          The output power delivered to the load is Vout * Iout. so if your output voltage is 3.3V and output current is 500mA, then the output power is 1.65Watts.

    The IC power dissipated is the sum of the power dissipated from individual factors like internal MOSFET switching losses, MOSFET conduction losses, body diode losses, IC quiescent current losses etc.

     IC_Pd = M_Pswitching + M_Pbody + M1.Pconduction + (Vin * IC_Iq)  + M2. Pconduction(if device has low side FET)

    You can look at the Operating Values table in WEBENCH that summarizes the total IC power dissipation loss as IC_Pd.  While calculating the junction temperature of the chip, you need to use the IC_Pd and not the output power and you can see this result in the WEBENCH Operating Values table as well.

    Tj = Ta + (IC_Pd * ThetaJA).

    The TPS5420 is available in an 8 pin SOIC package and it does not support a heat sink.

    Regards,

    Gerold

     

     

  • 0 in reply to Sesha giri
    TI__Genius 14455 points

    Hi Seshagiri,

       Yes. You cannot use a heatsink with the TPS5410D package as well.

    Regards,

    Gerold