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
Anyplace of note to source them?
> 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
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.
> On Fri, Oct 14, 2016 at 9:51 AM, Gene Heskett <ghesk...@shentel.net>
> > 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>
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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