LP2951CSD/NOPB (WSON PKG) - About power dissipation

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Guru 21045 points

Other Parts Discussed in Thread: LP2951-N

Hi Team,

Our customer would like to use LP2951CSD/NOPB (WSON PKG) at the following conditions.

[Customer conditions]

-Vin=24V

-Vout=12V

-Iout=60mA

-Pd=(24V-12V)*60mA=0.72W

-θJa=43.3℃/W

-Ta=70℃(max)

We believe that they can use LP2951CSD/NOPB at this condition.

Because, “Tj=Ta+(θJa * Pd)=101.2℃” at this condition.

However, according to “Figure 27. LP2951-N Maximum Rated Output Current” of the datasheet,

We can’t use this device…

Therefore, I would like to know whether this device is usable.

Regards,

Kanemaru

over 8 years ago

0 Donald Jones over 8 years ago

TI__Mastermind 22610 points

Yes, the LP2951CSD device (WSON/NGT) is usable.

Your calculations are correct.

The LP2951-N Figure 27 is from the original day one release (~1983) of the 'P' dual in-line plastic 8-pin package, soldered to a 2-layer PCB. From the chart I would estimate the RΘja to be approximately 111°C/W. This LP2951-N Figure 27 is out-of-date, possibly obsolete, as the present TI standard for RΘja is referenced to a 4-layer PCB (JEDEC JESD51-7) which will yield lower (better) RΘja values.

For Ta(max)= 70°C, Tj(max)= 125°C, and RΘja= 43.3°C/W the maximum allowed dissipation is 1.27W. Your calculated 0.72W is well below that point.

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LP2951CSD/NOPB (WSON PKG) - About power dissipation