I found out the hard way that my Arduino Pro Mini clone is not 100% compatible with the genuine one. On my previous post, when testing the Pro Mini clone, it was powered either from the USB-to-Serial converter or from a breadboard power supply. Today I tried powering it directly using its RAW pin from a 12V power supply, and I think the voltage regulator is now fried. No magic smoke or anything, but it no longer works correctly. I probed the output voltage by using my multimeter on the VCC pin, and it showed 3.123V when it should be 5V. Also the voltage regulator was very hot when I touched it. The uploaded sketch didn’t run but the board still consumed around 80mA to 100mA of current. The power LED only turned on during initial power up. However, when I powered the Pro Mini clone using 5V power supply connected to the VCC pin the sketch ran OK, but the regulator was still very hot. In short, I think I fried the voltage regulator.
On genuine Pro Mini, the voltage regulator should be able to accept 12V input (see that the “Board Power Supply” is 5V-12V for the 5V model). This is because the genuine Pro Mini uses MIC5205 LDO voltage regulator, which has maximum VIN of 16V. The genuine Pro Mini probably derated the VIN to 12V because of the small copper area on the Pro Mini’s PCB.
However, my Pro Mini clone doesn’t use MIC5205. The label on the SOT-23-5 package read LBMK, which does not appear in MIC5205 datasheet. The MIC5205 datasheet states that the labels are LBxx or KBxx, where the xx are supposed to be the fixed voltage output. So the expected label for 5V output is LB05 or KB05. So my Pro Mini clone is definitely using other SOT-23-5 voltage regulator.
After a bit of searching, I came upon this Reddit post asking for identication of LBMK labeled SOT-23-5 package that’s used as a voltage regulator on a Pro Mini clone. What a coincidence. The Pro Mini clone on that post’s picture is the exact same as the one I have, down right to the header pin configuration and silk screen and reset button color. The poster think that this SOT-23-5 LBMK is really XC6219B502MR-G from XC6219 series LDO voltage regulator by Torex Semiconductor.
So XC6219B502MR-G is pin compatible with MIC5205, but the maximum input voltage is not compatible. For XC6219B502MR-G the maximum input is 6V, so no wonder the regulator fried when I connected it to 12V. Looks like for my Pro Mini clone, I will have to cut off the XC6219B502MR-G and power the board using external voltage regulator from now on.