Has anyone used the Nexperia 74LVC1G74GS? - Page 1
Forum section: electronics / projects

author: seon
author_rank: Regular Contributor
timestamp: August 05, 2023, 11:32:26 pm
content: Hey folks,I've selected a Nexperia 74LVC1G74GS,115 for one of my project, and I'm a little confused about their mention of the part including Schmitt triggers on all inputs in point 1 of the data sheet."Schmitt trigger action at all inputs makes the circuit highly tolerant of slower input rise and fall times."https://au.mouser.com/datasheet/2/916/74LVC1G74-1512350.pdfIt reads like it includes them in package on all inputs, but the logic diagram on page 3 only shows one on the Clock input.On top of that, other vendors that make LVC1G74 like TI with their SN74LVC1G74 don't mention/have Scmittt triggers.Right now I've implemented an external Schmitt trigger in my design, but I'm super space constrained (hence using an X2SON8 part) and would like to drop the external Schmitt trigger.... but I'm just unsure about the Nexperia data sheet.Am I reading it correctly?Has anyone else used this part and can vouch for it having a Schmitt trigger on the clock input?Thanks!SeonUnexpected Maker

author: moffy
author_rank: Super Contributor
timestamp: August 06, 2023, 12:07:05 am
content: The data sheet certainly is ambiguous, the words say every input, the diagram says only the clock input. If it is a production item I would go for the common denominator between all manufacturers which is no schmitt triggers on the inputs. I have seen where relying on a particular manufacturers feature on a generic part has led, down the line to some baffling problems where purchasing departments have ignored the engineers instruction and used a generic part to the detriment of the product. If it's a one off then assume the minimum i.e. only on the clock until you get better info.

author: Kean
author_rank: Unknown
timestamp: August 06, 2023, 12:08:05 am
content: I haven't used it, but are you suggesting the datasheet might be wrong or misleading???NASA seem to think they do have a Schmitt trigger on the Clock inputs at least -https://www.nasa.gov/sites/default/files/atoms/files/techbul_20-01.pdfBut I note that the "Nexperia Logic Handbook" Oct 2020 states:QuoteElsewhere it mentions thatSchmitt trigger actionis a pseudo-schmitt trigger implementation with narrower hysteresis.I don't see Vt+ or Vt- specified in the 74LVC1G74 datasheet anywhere even for the clock input, but I do see input transition rise and fall rates in the recommended operation conditions. And that sentence near the start of the data sheet actually says "Schmitt trigger action" now that I read it again. Thus, the answer is yes it kind of does but with the limitation of max 10 ns/V transition times.So I believe you still need your external Schmitt trigger buffer to be safe if dealing with a hardware debounced push-button or similar, and probably should have one on your /SD and /RD pins if either of those use RC delays for a known power on state.Ref:https://static4.arrow.com/-/media/arrow/files/pdf/final_nexperia_logic_handbook_201029.pdf

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2023, 12:11:18 am
content: Quote from: seon on August 05, 2023, 11:32:26 pmThey've said that for a long time, so I'm sure it is correct.It it easy to check, but as you point out, it does constrain you to the Nexperia partThe Nexperia 74AUP1G74 says the same, so if you are running at 3.3V, that could be an 'alternate BOM' choice.there is also this dochttps://www.nxp.com.cn/docs/en/supporting-information/QIC-Schmitt-Triggers.pdfNOTES: 1. All AXP, AUP, and LVC Mini Logic functions have Schmitt trigger action at inputs. 2When I last looked intoschmitt trigger actionpins, the Nexperia and Diodes inc parts were appx 250mV VH (typ), so it is less than a formal schmitt VH spec, but still easily large enough to be usable.Diode inc specifySchmitt trigger actionon their 74AHC1G parts, but they do not offer a 74AHC1G74 FF.

author: seon
author_rank: Regular Contributor
timestamp: August 06, 2023, 12:25:35 am
content: Thanks folks - as Kean points out though, they claim "Schmitt Trigger Action" - so something that's kinda like Schmitt trigger functionality, but not exactly one?Their logic diagram clearly shows a Schmitt trigger symbol on the clock (which is all I really need one on).I'm the designer, manufacturer and purchasing department, so I'd not be swapping out for a "generic brand" and losing the functionality, but I'm also worried about not being able to get the part down the line (I need higher than 3v3 power source/logic input for them).SeonUnexpected Maker

author: moffy
author_rank: Super Contributor
timestamp: August 06, 2023, 12:41:28 am
content: Quote from: seon on August 06, 2023, 12:25:35 amThat is the advantage of multiply sourced parts and it can be a real gotcha if you depend on a single manufacturer.

author: seon
author_rank: Regular Contributor
timestamp: August 06, 2023, 12:49:02 am
content: Quote from: moffy on August 06, 2023, 12:41:28 amYup, keeping my external Schmitt trigger - it's the safest thing to do!SeonUnexpected Maker

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 06, 2023, 01:05:17 am
content: Quote from: seon on August 06, 2023, 12:25:35 amItisa schmitt trigger, just one with a smaller ~250mV hysteresis band.TI have a SN74HCS74, which has schmitt on all pins, but not yet in single-FF, so smallest is Dual D-FF in QFN15 at 2.5 x 3.0mm

author: liaifat85
author_rank: Regular Contributor
timestamp: August 06, 2023, 07:53:06 am
content: Sorry. I never used this IC. You can mail to Nexperia:info@nexperia.com

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 06, 2023, 11:46:54 pm
content: Many of the Nexperia discrete logic ICs have schmitt trigger inputs, even on "standard" references for which schmitt trigger inputs are not historically implemented.I've used both the LVC and AUP series and both have schmitt trigger inputs on all their references (except rarely when explicitely mentioned otherwise.)What it means though is that if you have designed around Nexperia discrete logic ICs and are expecting schmitt trigger action on inputs for correct operation, and further down the line change the ICs for equivalents from other vendors, your design may break. So be careful about that. Conversely, if you're using logic ICs in peculiar applications - using them in their linear operation region for instance - that can't work with schmitt trigger inputs, then don't use Nexperia parts.

author: seon
author_rank: Regular Contributor
timestamp: August 09, 2023, 08:47:55 am
content: I ended up going with the external Schmitt trigger as well, and I found a smaller packaged version so that also solved my space issue, which was why I was looking at removing it in the first place.Thanks everyone for the help and guidance!Cheers,SeonUnexpected Maker