Spice simulation of ICs - Page 1
Forum section: electronics / beginners

author: krapht
author_rank: Contributor
timestamp: November 14, 2010, 06:58:16 am
content: Hi,I've got a circuit drawn using a SE555P timer, which is basically updated 555 IC. Anyway, I'd like to simulate it in SPICE before having a prototype PCB fabricated. Trouble is, I can't find a SPICE model for the IC.No problem, right? I've got a datasheet that describes its characteristics. Is there a way to go from datasheet to spice model? I've got time and the inclination to teach myself anything I don't know about this process, so if anyone could point me in the right direction, I'd appreciate it.

author: krapht
author_rank: Contributor
timestamp: November 14, 2010, 07:28:02 am
content: Specifically, I'd really like to find a good reference book that talks about spice macro models.Something like this article:http://encon.fke.utm.my/nikd/Tranfer/198891-macromodel.pdfbut more comprehensive.

author: Simon
author_rank: Unknown
timestamp: November 14, 2010, 08:27:10 am
content: well you can draw a 555 timer with "discrete" parts and use it but it is very odd that a 555 timer is not in the library, one of the single most popular parts.What are the differences between the normal one and this one that you are using ?

author: Bored@Work
author_rank: Super Contributor
timestamp: November 14, 2010, 09:38:51 am
content: If you really need a model for this particular SE555P, and your spice package doesn't include one, you need to ask the manufacturer for one. If the manufacturer doesn't have one, you need to build your own, based on the SE555P's datasheet and your measurements.However, if you just need some 555 timer behavior, then grap a 555 spice model that comes with your spice, or one from the net and be done.If you believe that a spice simulation will guarantee that your circuit will work, then, well, it doesn't. It is often better to invest your time in the real circuit (e.g. building and measuring it), than wasting time in optimizing and trimming a spice simulation. A working simulation guarantees nothing. A working circuit, however, is a working circuit.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 14, 2010, 03:13:13 pm
content: yea! makes me wonder who built the pre-installed models? maybe just a normal person like us... or you. from a bunch of discreet components, well, i dont know!

author: Simon
author_rank: Unknown
timestamp: November 14, 2010, 03:15:52 pm
content: well if anyone remembers the old electronics workbench version 5.12 you could make a circuit and then save it as a "block" which you basically called up and used like an IC. I'm sure you can do it for spice and yes then pass it on

author: tinsmith
author_rank: Contributor
timestamp: November 19, 2010, 08:23:08 am
content: Quote from: Simon on November 14, 2010, 08:27:10 amAs a first-order approximation, maybe. It depends what you need. Building something as a single part on silicon versus many discrete parts gives significantly different results, it's not just a matter of the space it takes up on a PCB.

author: Time
author_rank: Frequent Contributor
timestamp: November 19, 2010, 05:04:48 pm
content: depends on the spice program but models typically arent produced by a discrete component hierarchy. Usually the hierarchy is done with virtual elements like voltage dependent current sources, feedback loops, and things of that sort. I guess you could create your model with discrete parts but this seems like it would siginificantly lengthen your simulation times.

author: Zero999
author_rank: Super Contributor
timestamp: November 19, 2010, 07:54:48 pm
content: Why do you need to simulate the 555 timer?There shouldn't be any need 99% of the time.The most likely reason is as an educational exercise.Here's the only 555 timer circuit I've actually felt the need to simulate, not counting college exercises. I wanted to check that the voltage across the bootstrap didn't get too low, when the 555's output is high.