Gene, Inline
On 10/14/2016 02:01 PM, Gene Heskett wrote: > On Friday 14 October 2016 14:45:31 Chris Albertson wrote: > >> Typically 0.1 bypass caps REALLY to have to be physically close to the >> load they are bypassing. Within a few millimeters. Cut the leads >> short and bridge the power pins with the cap. >> >> Placing a larger cap farther away can't cause any harm but it is not >> going to do the same job. >> >> Reason: The real world is not the same as theory. All caps have an >> internal series resistance (ESR). Think of them as a cap and resister >> in series and model them that way too when you design the circuit. >> The ESR of a .1uF ceramic cap is nearly zero, but for the tantalum, >> you need to look it up in the data sheet. >> >> Why physically close to the load. Wire has non-zero impedance. >> Mainly in this case it is inductive. You need to minimize the value >> of the inductor between the 0.1 cap and the device. Apparently the >> manufacturer wants a low impedance power supply. >> >> Draw the circuit schematic with a the lead wire inductance and cap's >> ESR shown then you can see that needs to be minimized. Don't worry >> about space you candy 0.1 caps that are the size of a large grain of >> sand > Anyplace of note to source them? Here is one in a 01005 package (Metric 0402) 0.016"L x 0.008"W - (0.40mm x 0.20mm) : http://www.mouser.com/ProductDetail/AVX/01016D104KATUA/?qs=sGAEpiMZZMs0AnBnWHyRQAwkDkDzLNakJDHmuCcZvLc%3d They are cheaper than the through hole caps that I normally buy. Hand soldering them will be a royal PIMA! >> The usual way to mount these is to make a tiny PCB that has the device >> on to and a mounting hole and the passive parts like the capacitor(s) >> and a connector for the cable. >> >> All that said, it will likely work OK if you can get that small ca >> reasonably close. Better to get the 0.1 closer then a larger one >> farther way as the goal is to minimize the amount of wire >> >> And using a larger cap is no substitute for the .01 either because I >> bet the .1 was spec'd mainly for its low ESR, not because it needed to >> be exactly 0.1uF >> > As a CET, I am well aware of all that, including the inductance of 2" of > wire. > > As for the ESR, tantalums are generally sub ohmic too. For half a > century or more. Its reverse bias that nails them to the fence, even a > few millivolts will do it eventually. > > Any caps on the leads will have to be not longer than the 667 is wide, > and not more than half its thickness. > > Thanks Chris. > >> On Fri, Oct 14, 2016 at 9:51 AM, Gene Heskett <ghesk...@shentel.net> > wrote: >>> Greetings everybody; >>> >>> A bit too cold this morning to go out to the shop and saw out the >>> thicker spacers I am going to need to permanently mount the Z motor >>> and screw anchor. >>> >>> So, not wanting to waste the day waiting for it to warm, I went back >>> to work on the encoder thing this morning. >>> >>> I now have an additional tab of alu extending to the left to hold >>> one of these ATS667's as an index pulse generator, and have that one >>> s-glued in a bit beyond where the center of the glued on screw >>> passes by, hoping it won't trigger on a regular tooth. >>> >>> But, I've never used any of these before. No clue as to their bad >>> habits. >>> >>> The spec sheet I have shows a "required" .1 bypass to ground on the >>> VCC lead, but has anyone had any problems using just one for all 3 >>> devices? This thing is cramped for space for a bulky mylar .1. >>> >>> So I intend to put an even larger tantalum on the pcb, which will be >>> on the left face of this added tab as I can let it project inward >>> nearly 20 mm's in that space, lots of space before encountering >>> anything that moves there. That means I'll have to paste some >>> wrapping wire to extend the leads about 1" to get to the pcb. So >>> this bypass cap may be as much as 2" of wire away from the device >>> body. >>> >>> Can anyone testify that the extra lead length is a problem? >>> >>> Thanks all. >>> >>> Cheers, Gene Heskett >>> -- >>> "There are four boxes to be used in defense of liberty: >>> soap, ballot, jury, and ammo. Please use in that order." >>> -Ed Howdershelt (Author) >>> Genes Web page <http://geneslinuxbox.net:6309/gene> >>> >>> -------------------------------------------------------------------- >>> ---------- Check out the vibrant tech community on one of the world's >>> most engaging tech sites, SlashDot.org! http://sdm.link/slashdot >>> _______________________________________________ >>> Emc-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users > > Cheers, Gene Heskett -- MC Cason Eagle3D - Created by Matthias Weißer github.com/mcason/Eagle3D ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
