Worst pinout ever - Page 1
Forum section: electronics / general

author: Terry Bites
author_rank: Super Contributor
timestamp: July 04, 2025, 01:00:08 pm
content: I'll chuck my hat in the ring with my pet hate, the 555.Single opamps bug me too.What do you find most anoying?

author: jpanhalt
author_rank: Super Contributor
timestamp: July 04, 2025, 04:09:23 pm
content: From the title, I was about to suggest the 555, but you beat me to it.

author: nctnico
author_rank: Super Contributor
timestamp: July 04, 2025, 04:38:46 pm
content: Actually, the pinout for most DIP and SOIC digital chips (74xx series) is pretty bad as the power pins are fartest apart as possible while for decoupling purposes, you'd like to have them next to eachother.

author: paul cotter
author_rank: Regular Contributor
timestamp: July 04, 2025, 05:56:12 pm
content: On smd '74 and cmos the distance between the power pins is compatible with a disc ceramic for decoupling, on dip versions they are a bit too far apart

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 04, 2025, 06:25:02 pm
content: A 74 series with mid power pins: the 74LS93.

author: hans
author_rank: Super Contributor
timestamp: July 04, 2025, 06:44:28 pm
content: Let's go even more annoying with even less pins: linear regulators or LDOsIs there any standardization in common packages? (SOT-23, SOT-223, TO220, TO263)Especially the SOT-223 bugs me. Yes its a nice package to tie onto a PCB heatsink. But then some use Vout as the cool tab, or use GND.The ones with Vout as tab will often put that pin the middle too, meaning that routing to the decoupling capacitors gets awkward.The ones with GND as tab are preferred (also because all my PCBs have GND planes already). But it still leaves the manufacturer freedom to flip Vin and Vout.I think all of these caught me by surprise at some point.

author: TimFox
author_rank: Super Contributor
timestamp: July 04, 2025, 07:49:00 pm
content: The change in the pinout for the 6AG7 pentode: originally, the suppressor grid was brought out to its own pin, like a 6AC7, but then someone decided to shift it to pin 1, which also connects to the metal shell.No good reason for it, and the military then had to add a warning label about removing power before touching the shell, since the suppressor is normally connected to the cathode instead of ground.This happened much earlier than the other complaints here.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 04, 2025, 08:15:40 pm
content: Quote from: hans on July 04, 2025, 06:44:28 pmSo bad that some have the exact same part with different pinouts depending on the suffix.

author: paul cotter
author_rank: Regular Contributor
timestamp: July 04, 2025, 08:15:54 pm
content: Tim, was that one of those black metal tubes(valves) with the octal base and an anode(plate) top cap? I haven't seen one of those for ~60 years. I had quite forgotten about them, had some once but I have no idea what I did with them, so long ago!

author: TimFox
author_rank: Super Contributor
timestamp: July 04, 2025, 08:59:54 pm
content: Quote from: paul cotter on July 04, 2025, 08:15:54 pmA black metal tube with octal base, but no plate or grid top cap.Typical grid-cap tubes (6J7, 6K7) were about the same height as the non-cap tubes (6SJ7, 6SK7), but the 6AG7 (designed for the output stage of video amplifiers, but used a lot in RF as well) had a higher plate power rating and was therefore taller.60 years ago, one often saw them used for crystal oscillators in the HF range.

author: ejeffrey
author_rank: Super Contributor
timestamp: July 04, 2025, 10:28:50 pm
content: Quote from: mikeselectricstuff on July 04, 2025, 08:15:40 pmThat I hate. The rest I don't really care about. Some of them (the single opamps) were annoying in the days of TH parts and 1 or 2 layer PCBs but these days I don't do extra work to use fewer than 4 layers. At that point the awkward pinouts aren't much of a problem.It's true than the standard 74 type logic chips have power pins in objectively bad locations for performance. But that's really a problem for the IC designer. If the chip can meet it's datasheet performance with its limit then it doesn't really matter.

author: paul cotter
author_rank: Regular Contributor
timestamp: July 05, 2025, 09:41:11 am
content: 6k7, that rings a bell, ok grid top cap, I got that wrong.

author: paulca
author_rank: Super Contributor
timestamp: July 05, 2025, 10:49:06 am
content: Z80 and family chips. Address line laid out on Monday, control lines on Wednesday, Data lines? Friday, back of a note pad in a bumpy taxi on the way home from the pub.The PIO chip has 6 data pins at one end and 2 all on their own at the extreme other end of the chip. WTAF?You do the addresslines and control lines and your PCB looks lovely. Add the datalines and dogs dinner.And in modern times, why can't MCU designers put an IO bank on one side of the chip? Whey do they insist in interleaving them across all 4 sides. 3 of B here, 5 here, 4 here... a few Cs mixed with one random A port bin and lets through the clock input pins right in the middle of that convenient little 4 wide sequencial group Can't have anything neat and tidy and easy to route like that can we?

author: rsjsouza
author_rank: Super Contributor
timestamp: July 05, 2025, 11:38:52 am
content: Quote from: paulca on July 05, 2025, 10:49:06 amThe reasons for interleaving these things might stem from specific requirements of the wire bonds inside the IC, but surely they can be extremely annoying.I am very familiar with the MSP430 MCUs, which fortunately have reasonable arrangements of pins such as theMSP430F149.(edit) as for very weird pinouts, the TPS54A20 is quite there on the list for me.

author: TimFox
author_rank: Super Contributor
timestamp: July 05, 2025, 02:39:09 pm
content: Quote from: paul cotter on July 05, 2025, 09:41:11 amLow-power tubes often had grid caps (e.g. 6K7). Higher-power and higher-voltage tubes (e.g. 807, 6DQ5) often had plate caps. Exceptions include some small metal Nuvistors: 7587 tetrode and 8058 triode with plate caps.

author: paul cotter
author_rank: Regular Contributor
timestamp: July 05, 2025, 08:27:37 pm
content: Those grid top caps must have led to stability issues with the long path involved. As a teenager I was interested in ham radio and I built a ham band double conversion superhet using var-mu frame grid pentodes, EF183(not sure what the American equivalent is) in the IF and I had severe difficulty trying to stop parasitic oscillation in the IF, even with metal screens across the bases to isolate grid and anode (plate) circuitry.

author: TimFox
author_rank: Super Contributor
timestamp: July 05, 2025, 09:11:34 pm
content: The grid caps were used long before the metal tubes were introduced, on full-size "ST" glass tubes, in order to reduce the capacitance between grid1 and plate that causes oscillation.The "single-ended" metal tubes introduced internal shielding between the grid and plate pins.During WWII, the famous E H Scott SLRM short-wave receiver for maritime-marine ships used a 6K7 (which by then was obsolescent) in the RF amplifier to reduce leakage from the local oscillator to the antenna; the remaining tubes were single-ended (6SK7, 6SA7, etc.).The EF183, AKA 6EH7, is a very high-gain tube, and must be handled carefully to avoid oscillation: grid caps were not used with the 9-pin "miniature" tubes, and the EF183 had an internal shield along with two cathode connections to help reduce plate-grid coupling.In a 6K7, the cap-grid wire is roughly the same length as the base-grid wire in a 6SK7, and IF transformers often allowed a wire through the top of the can to work with the grid cap.

author: Zero999
author_rank: Super Contributor
timestamp: July 05, 2025, 09:23:57 pm
content: LM723

author: David Hess
author_rank: Super Contributor
timestamp: July 05, 2025, 09:25:02 pm
content: Quote from: nctnico on July 04, 2025, 04:38:46 pmFor older ICs, the power pins are arranged that way to allow better routing of power and ground on two sided boards.Quote from: hans on July 04, 2025, 06:44:28 pmPower packages have constraints on their pinout because the heat sink tab connects to the substrate of the IC, which usually must be the lowest (most negative) voltage.

author: tszaboo
author_rank: Super Contributor
timestamp: July 05, 2025, 10:04:02 pm
content: External memory, SRAM interface on STM32 microcontrollers in LQFP packages. You are supposed to length match signals, and it's distributed on all 4 sides on the microcontroller. For a LQFP144 package, they are like 20mm from each other. If you also wanted to use the RMII interface, IDK how many layers you are expected to have, maybe 8 or 10.I ended up connecting it whatever, and told the software guys to use it at 1/4th the nominal speed and we are never to mention this again.

author: Whales
author_rank: Super Contributor
timestamp: July 05, 2025, 11:45:24 pm
content: Quote from: tszaboo on July 05, 2025, 10:04:02 pmSRAMandparallel LCD signals sprinkled around in clusters of 1, 2, 3 and (when you're lucky) 4 pins across all 4 sides of the chip. Surely the bondwires on the IC must look like a picaso, there is no way that the driver silicon for each of these interfaces is distributed all over the die.

author: tom66
author_rank: Super Contributor
timestamp: July 06, 2025, 09:46:49 am
content: The most frustrating thing for me is finding the perfect, say, buck converter IC, then realising it's Texas Instruments so it's in a WJFN29-5EPQ package with five weirdly shaped exposed pads and a rectangular footprint - I'm sure this is really only done to eliminate an easy second source, since if it was in a JEDEC package it would be a lot easier to clone functionally. (I wonder if they hold patents on some of these weird packages, arguing that they improve thermal performance or something like that.) It also means you have to draw a custom footprint for it.

author: Psi
author_rank: Super Contributor
timestamp: July 06, 2025, 09:57:03 am
content: Worse pinout has to be LEDs where the datasheet has part numbers for the matching red, green, blue versions but the green SMT dot marker means anode on some colors and cathode on others.

author: 5U4GB
author_rank: Super Contributor
timestamp: July 06, 2025, 10:17:41 am
content: Quote from: Zero999 on July 05, 2025, 09:23:57 pmThat one sorta makes sense when you realise it started as a TO-100 with reasonably sensible layout which was then bodged into a DIP package where they tried to keep some of the TO-100 layout while adding new bits and... maybe they'd had a few to drink beforehand.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 06, 2025, 01:56:53 pm
content: Quote from: Psi on July 06, 2025, 09:57:03 amOh, painful memory unlocked. Yeah, I had a board with some sort of LED backlight for a Lexan front panel. There was this pinout issue. We had to rework all the boards by hand to get the LEDs to light. The next rev I corrected the PCB, but for some reason, people still did the rework on the rev 2 PCB...Also, a Mini-Circuits part, I think a RF transformer, where a whole family of similar parts has clockwise pin numbers ... except the one we chose.

author: squadchannel
author_rank: Frequent Contributor
timestamp: July 06, 2025, 02:20:56 pm
content: 78xx and 79xx.I still tend to confuse pinouts.

author: David Hess
author_rank: Super Contributor
timestamp: July 06, 2025, 02:35:38 pm
content: Quote from: squadchannel on July 06, 2025, 02:20:56 pmThe odd pinout difference between positive and negative regulators comes about for the reason I gave. The tab is connected to the substrate which must be held at the most negative voltage.On a 7805, the most negative voltage is the common pin, so the input and output can be on pins not attached to the center tab. On a 7905, the input is the most negative voltage, so it must be on the center pin. The 317 and 337 vary from this because they are floating regulators so the most negative of their input and output is on the center pin, and their adjustment is pin 1.