EEVblog #1115 - Traps In Chips - And the 7660

Dave looks at some traps in chips and their modes of operation. In this case the TI LM2776, a look a the classic 7660 charge pump voltage inverter, and output ripple and ways to reduce it.
Parametric searching, and a look at some interesting rail inverters.

Support the EEVblog through Patreon!

Stuff I recommend:

Donate With Bitcoin & Other Crypto Currencies!

[testep]

Seriously Dave. I don't think people like man can stress the importance and value of videos like this. I'm a software engineer by trade, but consider myself an advanced hobbyist. Because I don't work in the industry or along side other electrical engineers, these "gotchas" aren't things that people like me get to see. Honestly, I'd almost be prepared to pay for your time to do a video each week just like this one. Just a brain dump of little tips and tricks just like this. Not only do we get to learn something new, but we also get introduced to parts that maybe we didn't know were even out there or how to use them properly.

[JohnAudioTech]

I used a 555 as an inverter once. It wasn't critical but did the job.

[DafyddRoche]

you think designing circuits on PCB's is tough, you'll find silicon even harder to design in. In my 15+ years in Semiconductors, I'll openly tell you, EVERY part has gotcha's. EVERY part has compromises that were made for time to market, cost, power or size. Good product definers at Semi manufacturers do their best to minimize those gotcha's impacts in their target markets.
The test of a good design engineer is to find what compromises were made, and decide if it impacts your product negatively.

[MrDehicka]

I'm using LM27762 Dave mentioned at 24:31 to generate clean bipolar supply in photodiode amplifier. Smallest BOM area and count definetly, and works like a charm.

[kevincozens]

This shows why Dave mentioned spending days/weeks/months in part searches for projects in some of his other videos. Dave is right about searching by function for the 7660. I did notice that if you search by the Charge Pump entry under Topology you do find the parts. Part selection is so much easier when you just want to make something for yourself that isn't going to have a major production run.

[FlakeSE]

New segment maybe? Part surfing Saturdays?

[dillonaumiller]

Great video. I didn't even know about those bias generators. There are so many ICs out there; always something new and interesting to find!

[ChrisBode]

At 2:40 you're only finding 7660 on digikey because you had that typed into the search within results box and it applied a "7660" filter at the same time as the charge pump filter. Without that extra filter, your LM2776 is the 7th result.

[Chupacabras]

Dave, you have goofed the searching filter. You have "7660" in the filter, so it's not surprise that no other chips than 7660 were found.

[ernestuz]

Honestly, what scares me of that chip LM2776 is that the ripple changes its frequency over several decades. Great video!

[brandi]

So the moral of the story is learn to read data sheets before you use a part.

[worroSfOretsevraH]

More datasheet analysis/explanation videos Dave! We learn a lot from these.

[dotdissonance]

Two excellent engineering related videos in a row! Thanks a lot. I know most people want the mailbag (I do love it as well), but the good technical videos are why I subbed years ago. It's also cool to see you get your nerd on. Great job!

[billmoran]

Great advice. There are so many traps in selection of parts. It's great to hear your views and recommendations.

[pausmth]

Come on Dave! When you searched digikey you still had 7660 as a search term. Also you could have selected negative under the output configuration selection to get the inverters... Anyway just 5 minutes in and that was bugging me. Seems like a good video otherwise. (Although I could certainly be missing something, just a basic hobbyist)

[qwirq]

"The problem is that we're literally only getting the 7660's here..."

Search Entry: 7660

[Antiath]

And I'm just designing a noise sensitive project with this part. Nice Timing. Thanks Dave !

[pepesworld]

thanks for this dave. we recently found the high speed dc/dc converter and we're so stoked waiting for it to arrive. the low output ripple is everything for us.

you're a hero to us mortals. giz kiss <3 muah muah.

[OmarMekkawy]

I really liked this deeply technical video. I am almost watched all of your videos multiple times. Really they are good.

[jaredwright]

I had to deal with a bunch of devices where the power supplies failed, and I remember seeing something like the PFM mode in the datasheet for the switching controller when under low/no load conditions. This video makes me wonder if high ripple could have been the reason diodes on the buck converters kept burning with no load.