Hello Sir,
LP2992 Tj max is 125 degree C.
If our design is 12Vin and 3.3Vout , 65mA
PD is 0.56W so that refer to Theta JC is 122 for SOT23 package .
Will cause IC internal temp rising 69 degree C .
System ambient Temp budget will only 125-69= 56 degree C max <= Am I right ?
Many thanks !
Hi Terry,
It is important to understand that application specific conditions such as board layout, proximity to other heat sources, air flow, and ambient temperature will all impact the thermal performance of a linear regulator. We model our Thermal Information table on the JEDEC Hi-K board. This provides standardized layout and test configuration to compare the thermal characteristics of two packages and devices; however, your application specific conditions will impact the thermal performance in your application.
Until you have a layout, the Rtheta_ja metric is useful in early calculations when trying to determine your ambient temperature budget:
Tj = Pd x Rtheta_ja + Ta
Tj = (Vin - Vout) x Iout x Rtheta_ja + Ta
Your approach is correct to use the maximum operating temperature in order to calculate the maximum ambient temperature.
125 C = 0.56 W x 169.7 C/W + Ta_max
Ta_max = 125 C - 0.56 W x 169.7 C/W
Ta_max = 30 C
Please note that the WSON package has a much lower Rtheta_ja metric. As such, you will be able to dissipate more power within the WSON package than the SOT-23 package.
Very Respectfully,
Ryan
