I'm doing an analog design and I'm getting pretty annoyed with a small thing - the pinout on most SOT23-5 op amps. Basically, I can't figure out the reasoning behind this becoming the industry standard pinout. The only thing that's kinda advantageous is that you can put many of them above one another with a single power bus. The problem is that in most configurations you are tying IN- to OUT via some kind of feedback network (FB), generally a few passive components.
In the classic layout (displayed is the LT1800, but most others are the same) the OUT pin is on the other side of the IN- pin - the farthest possible place it can be. There's no nice way to route the FB network - you can:
- go to the other side of the board via vias
- go under the chip, which will disrupt your power routing
- do something else completely, but still, not a very elegant solution
Basically, you are limited by the pinout and anything you add to the op amp is unreasonably complicated.
But, by simply swapping OUT with VS+ you get a very nice solution - the OUT is right across the IN- pin, the power pins are close together, allowing a very convenient place to put a bypass capacitor, the IN+ is still close to the VS- (it's common to tie it to GND). The power can still be routed 'under' the device, or use vias, or something, no problems there.
There is another common pinout, such as the MAX4490 (
https://datasheets.maximintegrated.com/en/ds/MAX4490-MAX4492.pdf ), which is an improvement, but still, the power pins could be next to one another :-(
I noticed many devices where a simple swapping of a few pins would greatly simplify layout (I noticed a step up converter, can't think of the specific device at the moment ).
Now, this is not a major issue, just a minor annoyance, I can easily work with it. I just wanted to know, whether or not there's any particular reason that that kind of layout was chosen as an industry standard?