Help with CD4541 data sheet - Page 1
Forum section: electronics / projects

author: IconicPCB
author_rank: Super Contributor
timestamp: January 07, 2020, 10:07:50 am
content: I am presently looking at using CD4541 timer counter chip.Looking through the data sheets ( see ST micro data sheet page 6, DIGITAL TIMER APPLICATION subheading , last paragraph) :"... A set-up time equal to the width of the one shot output is required immediately following initial power up, during which time the output will be high..."I am at a loss to interpret this paragraph.Opinions are invited.

author: richard.cs
author_rank: Super Contributor
timestamp: January 07, 2020, 10:15:09 am
content: Yes, most of the 4541 datasheets are terrible, but generally each in different ways. I recommend reading the datasheets from other manufacturers of the 4541, and above all looking at the logic diagrams. The basic functionality is identical between manufacturers.

author: Ian.M
author_rank: Super Contributor
timestamp: January 07, 2020, 10:26:15 am
content: I'd interpret that as the one-shot 'digital timer' circuit shown triggers at powerup, producing its timed output pulse, even if MR is held low during powerup.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 07, 2020, 11:51:56 am
content: Richard.. yes they are not as clear and in fact this bit of description of operation is not mentioned say in nexperiedata sheet.Ian ,thank You. If this is indeed the case , it presents a significant hurdle to ensuring no illegitimate/ unwanted output can exist.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 08, 2020, 06:51:02 am
content: I looked at Texas website tech support and found a topic asking this very same question.The summary of TI support /product engineer was"...I am sorry for the lack of helpful answer on this question. These are some of our legacy parts that the information is not very clear on...."About as useful as tits on a bull.

author: Benta
author_rank: Super Contributor
timestamp: January 08, 2020, 07:19:07 pm
content: Quote from: IconicPCB on January 08, 2020, 06:51:02 amTrue. But in TI's defense, these are 40+ years old devices (originally from RCA)and have gone through several company acquisitions until they landed at TI. They are cent parts and no sane company would invest resources in them.OP: the ON Semi datasheet has the same formulation.IMO, It means, that no matter what you do, Auto-reset or Master-reset, the circuit will run one timing cycle before it can be retriggered by Master-reset.

author: aheid
author_rank: Regular Contributor
timestamp: January 10, 2020, 10:22:25 pm
content: Let's trim it a bit:"A set-up time X is required immediately following initial power up, during the output will be high"X = "width of the one shot output"So, without further context, to me it reads that after power on, the output will be high for a while.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 10, 2020, 11:08:34 pm
content: Aheid,Thank You for your comments.The problem is as follows if the timer is set for for ten minutes, will the output be high for that duration?Intuitively I do not think the designers of the chip would have designed such a problematic situation into the chip.

author: aheid
author_rank: Regular Contributor
timestamp: January 11, 2020, 10:30:11 am
content: Read the initial text again (page two, emphasis mine):QuoteSo to me the, the text you quoted is just saying that when you power on, the chip will start counting right away which will cause the output to be high until it has counted till the end. Note that in the application diagram where the text you quoted is from, MODE is low (tied to ground) and the Qbar output is selected (pin 9 tied high), thus output is inverted relative to the text I quote.