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TPS709: Continuous Max.power dissipation of TPS70930

Jason Hu27
Intellectual 910 points
Part Number: TPS709

Dear experts, I use the TPS70930 to drive LED. The input voltage of TPS70930 is 24V and output voltage of TPS70930 is 3V. The package of TPS70930 is SOT23-5(5 Pin). Contiune output currenr is less than 20mA.

What is the continuous Max.power dissipation that TPS70930 can wistand? I calculate the max. power is about (24V-3V)*20mA=0.42W. Will it will damage the TPS70930? Regards.

  • 0
    TI__Mastermind 36565 points

    Hi Jason,

    The TPS709 5 pin package has an ambient junction to thermal resistance of 212.1 C/W.  At 0.42W power dissipation this will result in a junction temperature rise of 89.082 C above ambient.  If ambient temperature is 25C (room temp) then this will cause the device to operate at 114.1 C, which is within the recommended operating temperature of the device.  The junction to ambient thermal resistance is specific to your board and layout, so if you are unsure how close you are to the 212.1 C/W you should test your hardware using the techniques in this App note:

    https://www.ti.com/lit/an/slva422/slva422.pdf

    The quality and reliability data for most devices is captured at 55C junction temperature. Operating above this temperature will result in reduced lifetime of the component. For the TPS70930DBVR device, the TI quality data is provided here.

    https://www.ti.com/qrp/report?opn=TPS70930DBVR

    Using the DPPM sample size calculator and the MTBF and FIT Rate Estimator tools (located at the links below) we can estimate the MTBF for a junction temperature of 115C.  According to the qualification data the MTBF at 55C junction temperature is 1e^10 and at 115C junction temperature it is 3.12*10^8.

    DPPM Sample Size Calculator
    https://www.ti.com/support-quality/reliability/DPPM-sample-size-calculator.html

    FIT Rate Estimator
    https://www.ti.com/support-quality/reliability/temperature-change-FIT.html

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 910 points

    Dear Stephen, if I change the package from SOT-23 to WSON, will it will be helpful to the life of TPS709? Then, please refer to below figure, the two circule in the red retangle are GND VIA? If they are GND VIA, can I add more VIAs to improve the heat dissicipation? Thanks. 

  • 0 in reply to Jason Hu27
    TI__Mastermind 36565 points

    Hi Jason,

    Yes the WSON package will be a better choice and we would recommend placing as many thermal vias from the ground pad to a ground plane as you can fit.  2 vias are shown here but if the fabrication house you will be using can fit 3 or more vias, that will offer you better thermal management and improved MTBF.  Additionally you can extend the ground copper on the same layer as the components are placed and add thermal vias from the surface copper as well.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    Intellectual 910 points

    Dear Stephen, thanks for your help.