It's official: I hate op amps in SOT packages - Page 1
Forum section: electronics / general

author: temperance
author_rank: Super Contributor
timestamp: September 03, 2024, 08:59:22 pm
content: Management: our competitors have op amps in SOT23-5. We must follow. But can't we wire the op amp in reverse in the package? Anyone falling for our trap will be stuck. But engineering cost must not exceed 3 cent.Engineering: maybe we can swap VDD and VSS with some effort without exceeding the three cent budget.Management: ok, do it.One year later:Management: darn, our competitors are snatching away our profit. They copied our VDD/VSS reversed scheme.Engineering: with some effort we can also swap the inputs.Management: We lost millions last year. No matter the cost we swap the inputs so that anyone falling for our trap will be stuck.One year later:Management: you stupid engineering staff. They copied again our reversed input layout.Engineering: we can turn the die around such that all pins are swapped and give this part a new number.Management: You sir, have Excellent ideas and will be rewarded with our prestigious excellence in engineering reward.

author: hans
author_rank: Super Contributor
timestamp: September 03, 2024, 11:40:06 pm
content: Ah yes. Makes it especially fun to find&order alternative opamps for a design. Like.. oh I don't know if this one has enough bandwidth, let's pick another one that fits the project spec.Ugh! The inputs are reversed! Or everything is tilted by +/- 90 degree. Or we accidentally ordered the SOT-323/SC-70 variant which has a different pinout again (but could have fitted with some extra effort)! Oh no, this variant also has a shutdown pin, but the board has nothing provisioned for that pin, and the GND is obviously on the other side of the package, so the fix requires extra useless effort.

author: wraper
author_rank: Unknown
timestamp: September 03, 2024, 11:45:36 pm
content: There is a very good reason for reversed pin order compared to larger packages. It's die usually being upside down in such package. And it's hardly a problem.

author: coppercone2
author_rank: Super Contributor
timestamp: September 04, 2024, 01:05:33 am
content: everyone should filter that package out to reduce the market demand

author: floobydust
author_rank: Super Contributor
timestamp: September 04, 2024, 02:22:57 am
content: Same pinout hassles with SOT-23 comparators. I know of at least 3-4 different pinouts and an app note called two of them the "standard North West Pinout" and the "standard South East Pinout"ExampleMCP6566is offered in any of three variations per the pic.

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 04, 2024, 03:01:32 am
content: I obviously prefer to have more options in the same layout, until I realize the "standard" variant is the one that put inverting input diametrically opposite to the output. So I guess I equally hate them now.Although for such small packages it's much more likely for the center pin to be one of the supply for mechanical reasons. At least until someone decides it isn't...

author: Siwastaja
author_rank: Super Contributor
timestamp: September 04, 2024, 09:01:51 am
content: I have never these kind of problems. Years ago I came up with this semi-rigorous engineering process:1) Come up with specification i.e. requirement list for parts2) Use Digikey/Mouser parametric search to find suitable parts3) With more than one suitable part with all good availability, sort by price,4) Check second-sourcability in advance. This means comparing key parameters in datasheet.Pinout and package measurements are the first to be checked.Do not assume anything. E.g. package naming is meaningless. You only look at the drawings5) Draw the footprint in EDA6) Design the PCB as usualTLDR, solution to wrong expectations/assumptions is not to have those expectations/assumptions.

author: temperance
author_rank: Super Contributor
timestamp: September 04, 2024, 12:11:47 pm
content: @ SiwastajaI'm not stuck with a unique part. While looking for alternate parts and after viewing about twenty data sheets I ended up ordering one with the supply pins reversed. I'm probably not the only one.

author: phaeton
author_rank: Newbie
timestamp: September 04, 2024, 02:26:38 pm
content: Quote from: wraper on September 03, 2024, 11:45:36 pmSo then you just bend the pins upward and flip the chip upside down, right?

author: H.O
author_rank: Frequent Contributor
timestamp: September 04, 2024, 04:35:19 pm
content: Me, having run into that problem? No, not ever....Placed MCP6L01 where it should've been an MCP6L01R (or perhaps it was the other way around). Next order I got the SOT323/SC70 instead of SOT23 the footprint was meant for. No others fault but my own obviously but yeah, aarghh....

author: Siwastaja
author_rank: Super Contributor
timestamp: September 04, 2024, 06:39:31 pm
content: Quote from: H.O on September 04, 2024, 04:35:19 pmYeah. The key to success is to get rid of the weird mental pattern of "only X first characters/numbers of part numbers are meaningful". Especially old-schoolers do that mistake, but it never was really true.Once correct part is found from Digikey, copy-paste to schematic/BOM. When ordering more, copy-paste from BOM to Digikey. Copypaste once more to browser's Search field, and it will highlight the part number to you if and only if it completely matches, and you will obviously see if there are extra letters.Problem solved