I am fairly new to electronics and have done my first project successfully (where it works as assembled PCB). And I am looking for the next step there. In my original project I've used SPX3819M5-L-3-3 to regulate incoming 5V (from micro-USB) into 3.3V.
I am now looking to switch from micro USB to UCB-C connector, which can go up to 20V (the circuit is not the main sink, so another connected device can request up to full 20V). Given that original regulator maximum rating is 16V, I need to change it to something suitable. I've looked at TL760M33 for this purpose as it can go up to 26V and output fixed 3.3V at 500 mA max, which seems perfect for my case.
Being very new to electronics I have my doubts over every single detail.
So in this case my question is — is this replacement valid and would my circuit function as I expect it to? Additionally I wonder is there any pitfalls or details I missed in choosing a replacement regulator?
Original schematic:
Replacement schematic:
Best Answer
The data sheet value for the thermal resistance between junction and "ambient" (when the tab is soldered to a 15 mm x 16 mm copper area of 1 oz/sq foot thickness) is 55 °C per watt of power dissipated: -
If you supply 20 volts to the regulator and it drops 16.7 volts in the process of producing 3.3 volts at the output, AND the output current is 300 mA, the power dissipated is about 4.9 watts.
This means that the device's "junction" (when mounted as per above) will heat up 55 x 4.9 °C above ambient i.e., in an ambient of 25 °C the junction will warm to 295 °C and this is clearly too much. You should also note that the local ambient will rise significantly above the average ambient under heavy dissipation situations.
So, you need either: -