Know of an SOT89 vreg with this pinout? - Page 1
Forum section: electronics / projects

author: sleemanj
author_rank: Super Contributor
timestamp: January 20, 2018, 11:39:54 am
content: So, yeah, I farked the pattern for a the HT7550 regulator on a bunch of boards, swapped Gnd and Vout.This is what it is supposed to be....This is what I put on the boardsThe specs of this reg are not critical in the slightest, so if I can find one with the pin out I used it would solve the problem... but try as I might I can't find any SOT-89, or even SOT-23 (I could make it fit easily I think) that match my screwed up pin out.So, anyway, I figure it's worth posting to see if anybody knows of one, don't care if it's a name-brand or some dark chinese part, I'm sure I'm not the first person to make this particular cock up.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 20, 2018, 03:28:42 pm
content: No idea offhand, but if you need rework options, the correct part can be placed upside down, or tilted at an angle so the leads touch. Obviously this will have shit power dissipation, which could be enhanced by tacking on a copper flag. Or if there's space opposite the pins, it can be placed flat on the board, rotated 180, again not having much dissipation but at least it's not a faff.Is there a TO-92 version of that part?Tim

author: sleemanj
author_rank: Super Contributor
timestamp: January 20, 2018, 09:24:21 pm
content: Quote from: T3sl4co1l on January 20, 2018, 03:28:42 pmYes, I had that same idea, and probably will do a bodged to-92 surface mount if it comes to that.

author: phil from seattle
author_rank: Super Contributor
timestamp: January 22, 2018, 02:36:26 am
content: In the realm of hackery, go dead bug style. Turn the chip over, bend the pins and tab down and use wires if that's not enough. It's ugly, will work and earns you serious EE hacker cred. I rescued more than one disaster that way. Mostly just to keep going debugging a board. Post pictures and put one up in your work space to remind you to verify your chip footprint before send the PCB off to be fabbed.But for peace of mind and order in the universe, reorder the PCB...

author: slugrustle
author_rank: Frequent Contributor
timestamp: January 23, 2018, 05:53:33 am
content: I wonder if there is any physical or design reason for certain pinouts.There are 6 permutations:{Vi, GND, Vo}{Vi, Vo, GND}{GND, Vi, Vo}{GND, Vo, Vi}{Vo, Vi, GND}{Vo, GND, Vi}AP2204https://www.diodes.com/assets/Datasheets/AP2204.pdfcomes in three of the permutations: {Vi, GND, Vo}, {GND, Vi, Vo}, and {Vo, GND, Vi}AZ1117Chttps://www.diodes.com/assets/Datasheets/AZ1117C.pdfcomes in two of the permutations: {GND, Vo, Vi} (new) and {GND, Vi, Vo} (shared with AP2204)I spent some time looking and haven't seen either {Vi, Vo, GND} or {Vo, Vi, GND}.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 23, 2018, 06:57:35 am
content: Tab is substrate, which is almost always the lowest potential (GND or output, or input for negative types), or the collector/drain (LDO and negative output). Sometimes it doesn't have any relationship (or an obvious one, anyway).The two (wirebonded) pins can be either way around, which is something you need to note carefully going between TO-220 and SOT-89 packages, which are often mirrored of each other (which...heh... well, now we have this thread I guess).That doesn't really rule out any permutations overall, but among just positive regulators you're very likely to see only 4 of those permutations.I don't know why they sometimes swap the two pins, but it's clearly something to do with packaging. Which means it's perhaps unlikely you'd find a SOT-89 that is pinned "wrong"... but who knows?Tim

author: ArdWar
author_rank: Frequent Contributor
timestamp: January 24, 2018, 05:30:41 am
content: Not sure for Vo-Vi-GND.But if it's Vi-Vo-GND, you might get away with 5-pin SOT-23 (assuming the usual center-pin = tab)