What do these datasheet dimensions mean? - Page 1
Forum section: electronics / general

author: MassDestruction
author_rank: Contributor
timestamp: April 17, 2018, 05:40:52 pm
content: Hey GuysI'm reading through a datasheet in order to create a footprint for an IC, but I'm confused what the dimensions actually mean. I included an image of whats confusing me. Here is a link to the datasheet alsohttp://www.ti.com/lit/ds/symlink/txb0108.pdfIts on page 26 of the document, and the part is the TXB0108.Now whats really confusing me are the dimensions that look like fractions. So the dimension representing the width. Is that a max of 6.6mm and a min of 6.4mm?Also why are commas "," being used instead of dots "."? Every other datasheet I've looked at has used dots(including this one in other parts of the doc) so that's confusing me as well.Also what does this graphic mean?

author: Nusa
author_rank: Super Contributor
timestamp: April 17, 2018, 06:14:38 pm
content: commas vs periods for a decimal point:Short answer: Different countries follow different rules on notation. Deal with it when you encounter it. The person who made it was following the rules of the country and location he was in.Long answer:https://en.wikipedia.org/wiki/Decimal_separatorI was educated on multiple continents in the pre-computer age as a child, so several times I ran into such notation issues hard when transferring schools. If you didn't use the right notation for the locale, your answer was usually marked wrong by the teacher. The decimal point is just the most obvious difference..there are some other gotchas.

author: ataradov
author_rank: Super Contributor
timestamp: April 17, 2018, 06:20:02 pm
content: Also, that additional box is a standard tolerance notation. Here is the first link I googled that gives some explanationhttp://www.sharptechdesign.com/Tutorials/ProE_Fundamentals_WF2/WF2_Lesson49.htmBut generally you don't need to worry about that stuff for components.And periods in numbers is one of those US things, since US does not want to adjust to what the rest of the world is doing.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 17, 2018, 08:48:56 pm
content: https://www.google.com/search?q=geometric+dimensioning+and+tolerancingOffhand, going from top to bottom, left to right:- These are all in mm by default, by the way. There should also be a projection graphic (a cone frustrum) showing third angle projection. (American drawings are often inch and 1st angle, so watch for these features.)- 0,65 = pin-to-pin spacing, on centers. Reference dimension, no tolerance. (A reference is toleranced by a separate declaration.)- 0,30/0,19 = pin width, max/min.- Crosshair 0,1 (M) = centering, circular, radial tolerance, maximum material condition (MMC). ("(L)" would be LMC.) This makes sense, as pins would be likely to bend in random directions, and you would expect maximum deflection at maximum length.- Triangle D = this dimension with respect to datum D. Find the datum declaration elsewhere in the drawing.- 4,5/4,3, 6,6/6,2 = max/min width of body and length of pins, respectively. Nice, the pin length spread isn't horrible, that means you don't need a lot of excess toe on the footprint.- And 6,6/6,4 triangle C = you should be able to guess what this is now: body length with respect to datum C.HTH,Tim

author: bitwelder
author_rank: Super Contributor
timestamp: April 18, 2018, 09:22:09 am
content: Does the box around the 0,65 in the top left corner have any special meaning, or it is just to clearly identify that it refers to the measure pointed to the near arrows?

author: spudboy488
author_rank: Regular Contributor
timestamp: April 18, 2018, 11:29:03 am
content: It's the pin "pitch". That's the standard distance between all the pins.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 18, 2018, 09:54:57 pm
content: Basic dimension:http://www.sigmetrix.com/gdt-symbols/Tim