Perhaps You could help me confirm my thermal discussion on choosing appropriate LDO?
MIC5225, a 16Vin and 150mA output current quaranteed LDO. So, parameter-wise I would guess that I could use this SOT23-5 package and get it to run from f.i 14Vin to 3.3Vout and 100mA output.
I checked some relevant Q/As about the 'LDO power dissipation' topics:
(can't provide links, since not enough rep)
- "LDO selection in Thermal point of view"
- "SOT-223 Thermal Pad and Vias" (many references also)
According to a potentiometer model [http://www.ti.com/lit/an/slva118a/slva118a.pdf], the power dissipated is equivalent to the input and output voltage difference and output current. So
(14Vin - 3.3Vout) * 100mAout = 1.1W. (getting suspicious)
Based on my readings, SOT23-5 (with 235C/W of thermal ambient resistance) can't handle it with such input voltage.
(125C - 25C)/235[C/W] = 0.426 W (So when ambient is 25C, the package could dissipate 426mW) no-airflow
I conclude that it's false to expect the regulator to work up to 16Vin and 3V3, 150mA, even though it's advertised as such (Couldn't find any other package for this either). Why false advertise xD?
I then chose LD1117S33TR with SOT-223 which should manage 1.1W with some heat sinking. Space is also quite scarce. Package thermal resistance is ~110C/W. So perhaps package-only could dissipate:
(125C-25C)/110[C/W] = 0.91W
and with some heatsinking on PCB and airflow it should be fine? I wonder if this train-of-thought is correct?