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ADS124S06: About thermal resistance

[FAE] Andrew Wang
Genius 10685 points
Part Number: ADS124S06

Hi Team,

Quick question.

(1) Customer would like to know which package of ADS124S06 generate less heat. I think it's VQFN, please correct me if wrong, thanks.

(2) From thermal resistance table, we should reference to this value -> Junction-to-board characterization parameter, correct? 

(3) If total current is estimated at 2mW (using VQFN package), then we can calculate the total thermal rise at around 2mW * 15.7 C/W = 0.03 °C, correct?

Thanks.

Andrew

  • 0
    TI__Guru** 112725 points

    Hi Andrew,

    In most cases more heat will be dissipated through the PCB rather than through the top-side plastic.  Theta measurement values as thermal resistance relative to the junction are tested based on a specific condition and may not take into account all thermal paths.  For the QFN package the mounting structure has a pad under the chip which will dissipate the heat more quickly than a package without the pad.  So the measure is not the heat being generated, but rather the ability to dissipate the heat generated more quickly.

    The thermal characteristics (Psi) can help with calculating the device junction temperature not as a resistance value, but rather the ability to dissipate the heat from a number of ways as determined from a characterized method.  The Psi junction-to-board characterization parameter  will allow calculation of the junction temperature relative to the PCB temperature.

    If we assume that the junction temperature matches the PCB with no power dissipating through the device, then the thermal rise of the junction will be as you stated in (3).  The overall temperature of the PCB is most likely affected by other components, so the PCB temperature most likely will be dynamic.  This will in turn affect the junction temperature in time.

    When calculating the overall temperature of a board level system, the power dissipated by the IC will be the same whether it is the TQFP or the QFN, however the QFN will dissipate the heat more quickly out of the package to the PCB and in turn having a lower junction temperature as compared to the TQFP package.  The overall heat generated will need to be considered separate from the just the IC as the IC will start to heat the PCB.

    Best regards,

    Bob B