Typical application circuits in datasheets - Page 1
Forum section: electronics / beginners

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 20, 2017, 11:09:49 pm
content: There comes a point where solderless breadboards or even point to point wiring doesn't cut the mustard any more. Especially when dealing with small SMD components, designing a small PCB and having it made can be the better option. That leaves me with the following question: can typical application circuits be simply copied to end up with something functional, or are they just a rough and ready example that requires interpretation and improvement? I can imagine there always being ways of improving things, like input protection or filtering, but are the examples good enough to be usable?I guess that in some cases they obviously are, as sometimes specific layout examples are also given, but I am not quite sure how this translates to other components.

author: Zero999
author_rank: Super Contributor
timestamp: August 20, 2017, 11:28:20 pm
content: I've seen countless designs which are simply copied and pasted from datasheets so I'd say yes but never just put it into production, without ant prior testing, get one or two prototypes made first.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 20, 2017, 11:47:15 pm
content: Quote from: Hero999 on August 20, 2017, 11:28:20 pmYes, that seems obvious to me, although I'm sure people have fallen on their faces with thatVerification is always essential, I'd say before and after system integration. I'm familiar with product development and which steps are required to bring a viable product to market, it's just that electronics never have been part of the deal.Oh, and of course I do understand that high speed signal circuits and such will be more finicky, like modern FPGA and computer boards or RF circuits.

author: Audioguru
author_rank: Super Contributor
timestamp: August 20, 2017, 11:47:25 pm
content: Applications circuits shown in datasheets assume that you know that the circuit needs supply bypass capacitors and shielded input cable that are not shown.

author: Rerouter
author_rank: Super Contributor
timestamp: August 21, 2017, 02:27:37 am
content: Not to mention, most datasheets will include calculations for selecting components where the value matters, e.g. maximum current from a pin, threshold of an enable, etc,I've been bitten by a few example circuits before, e.g. a 3.3-5V level shifter, in the diagram it had the enable pin driven on the 3.3V side, but the minimum input for logic high was 3.7V. which meant a bodge to test and a respin.

author: Mr. Scram
author_rank: Super Contributor
timestamp: August 22, 2017, 07:10:59 pm
content: Does anyone else have any great stories about how they got bitten by reference designs?Quote from: Rerouter on August 21, 2017, 02:27:37 amTaking a good look at the datasheets can't hurt.

author: Benta
author_rank: Super Contributor
timestamp: August 22, 2017, 08:18:49 pm
content: QuoteYES!My favourite one is the 4046 datasheets. This includes CD4046, MC14046, 74HC4046 etc.They show a passive loop filter (I prefer calling it a loop controller) for using the edge-triggered PFD. Problem is: it won't work.For a type-2 PLL (zero phase difference between the inputs), an integrator is needed in the loop controller, which the application circuit will not provide.Never got bitten though, as I did a deep-dive course on PLLs at the university and accordingly designed my circuits with an active filter.But I do wonder how many people have torn out their hairs over this application circuit after building it...

author: dmills
author_rank: Super Contributor
timestamp: August 22, 2017, 08:27:11 pm
content: TI class D power amp, app note looked good, on a quick look but didn't work....Turns out there was an error of three orders of magnitude in the snubber caps, so much current flowed that things were unsoldering themselves.Regards, Dan.