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TPS796: Dropout voltage & Thermal information TPS79650

Part Number: TPS796

if we compare DRB(VSON) package vs DCQ(SOT-223),  RθJA Junction-to-ambient thermal resistance of DRB(VSON) is very much small compared to DCQ(SOT-223): but package area of DCQ(SOT-223) is much more than DRB(VSON), i am under assumption RθJA Junction-to-ambient thermal resistance decreases with increasing size as seen in most cases of regulators. thermal data provided is correct?

whats the maximum, over temperature drop out voltage for TPS79650 @ 1A?

  • Hi Madiwalesh,

    Package size is only one minor factor in how heat is able to get out of an LDO. Other factors include die size, die orientation in the package, die location in the package, mold compounds, and more. Perhaps most important to TPS796 the size and location of the thermal pad or GND tab relative to the die is important.

    The die for TPS796 is able to sit on top of above a large metal path to GND for both the DRB and KTT packages, but not the DCQ package. Since the main heatsink for an LDO is the GND plane of the PCB, this more direct path for heat to reach GND allows more heat to leave the LDO reducing the junction temperature more than the less direct path of the DCQ package. As such, when the junction temperature is compared to the ambient temperature, there is a smaller difference and therefore a smaller RθJA.

    Very Respectfully,
    Ryan
  • Hi Ryan,

    Thanks for the reply, it was very helpful. i did not understand this sentence: As such, when the junction temperature is compared to the ambient temperature, there is a smaller difference and therefore a smaller RθJA.

    and Whats the dropout voltage for TPS79650 @1A current?
  • Hi Madiwalesh,

    The following Application Report describes how RθJA is generated.  Both the ambient and junction temperature are measured with a known amount of power dissipating in the LDO.  We then calculate RθJA as (Tj - Ta) / Pd.  Since the junction temperature for the DRB and KTT packages is lower than the junction temperature of the DCQ with the same ambient temperature and power dissipation, RθJA is also smaller.

    The dropout voltage for TPS79650 at 1 A is specified in the Electrical Characteristics table as 200 mV typical and 300 mV maximum.

    Very Respectfully,

    Ryan