Mystery relic Microchip SOT style chip identify please? Looked everywhere

[TnF]

I've looked everywhere, the package is same "length" as SOT-89 (4.5mm) but width is larger ~3-3.1mm, and has only 3-pins similar to SOT-23 instead of SOT-89 3+tab.

2nd pin (middle) is directly connected to ground.
3rd pin (right one) 1V forward voltage drop to ground and 0.5V in reverse. Looks like it's directly connected to +5V from a regulator.
1st pin (left one) no forward voltage drop across but it's connected in circuit, 0.5V in reverse. Reads +5V in operation and goes to MCU reset pin.


The whole board is made in Japan in the 90-00's and uses almost exclusively Japanese branded components. Weirdly this one is branded Microchip. I've even went into checking Microchip's acquisitions thinking it might be a rebranded component.

Came across these but haven't yet checked all variations, the package and brands differ but it could be a copied design.

Any ideas? Thank you

edit: Added pin 1 connection
edit2: MCU Reset pin description:

[amyk]

Not Microchip, but Mitsumi.

PST600DM in MMP-3A package.

[TnF]

Not Microchip, but Mitsumi.

PST600DM in MMP-3A package.

Thanks a lot! You are godsend ;p
I saw this brand while looking, searched for the logo too but didn't do a good job it seems;p To be fair they look identical 
I wonder though, where/how did you actually find it?

[pcprogrammer]

I tried to look at the by amyk linked pdf file but my system warns for a potential risk, so here is a link to a safer source for this datasheet: https://www.digchip.com/datasheets/parts/datasheet/304/PST600-pdf.php

[TnF]

I tried to look at the by amyk linked pdf file but my system warns for a potential risk, so here is a link to a safer source for this datasheet: https://www.digchip.com/datasheets/parts/datasheet/304/PST600-pdf.php

Warning is because it's http instead of https link. Just stupid chrome things. Are you worried of a man-in-the-middle attack on a random datasheet?   

[pcprogrammer]

I tried to look at the by amyk linked pdf file but my system warns for a potential risk, so here is a link to a safer source for this datasheet: https://www.digchip.com/datasheets/parts/datasheet/304/PST600-pdf.php

Warning is because it's http instead of https link. Just stupid chrome things. Are you worried of a man-in-the-middle attack on a random datasheet?   

Firefox just refused to download the PDF, so I searched for another one. 

But nowadays you never know what the hacking idiots do out there, so better safe then sorry.