X7R is somewhat temperature stable, but not very voltage stable according to the Taiyo Yuden data.
Google found this,
http://ds.murata.co.jp/simsurfing/mlcc.html?lcid=en-us
which is quite a nifty quasi-spice curve generator. Pick almost anything to graph…
About 30% reduction for a Samsung X7R 50V part at 30V.
In 1206 size, there is plenty of choice at 4.7uF/50V
Ohms Law.
2 of whatever you can buy will halve the ESR.
Just to mention: both Digikey and Mouser have techs. If you call their ordering number, just ask the nice person you need to talk to a tech. They are very knowledgeable and can help you.
Pro tip: When you get a job as an EE (assuming you do), There are three sets of people you do not want to piss off: Techs, Admins, and the Mafia. They can make or break you.
Admins and Techs should be obvious. They are like NCO’s in the military. They keep the place running. They fix the mistakes. They know everybody. As an EE, you are dependent on the techs. As an employee, you are dependent on the Admins.
You are likely to be in a production environment at some point. The Mafia are usually a few little old ladies who have been there since God was in short pants. If you piss them off, you will never get any help to do anything. Be nice and polite to them. Just sit in the production area and see who goes to whom. Once you know who they are, approach politely and introduce yourself as the new guy. They will know that already. You might want to bring a nice ceramic bowl and a big bag of M&M’s. Say you have this gift so that, in the future, if you get in a crunch (which you will), you just want them to remember you. They will know why.
Also remember they will be watching you. If you are an ass to others, they will remember. If you are a hard worker, professional, and polite, they will know. They are the center of an efficient rumor and information network. And, if you complain to their boss, you should start looking for a new job.
Interesting statement and all too true. However in my experience there are mostly two types of people, Those who intuitively know what you are saying and those who will never will.
I first read this thread after post #7 and quickly fell into the old lady group you mentioned.
And sometimes you’re better off not knowing what they did to keep things running. (Especially the techs.)
In which branch did you serve? Comparisons like this are unlikely to be accurately understood or appreciated, since few engineers or managers ever wore a uniform.
Dale
Never did - 4F - I have one hand, thus the “one-armed bandit”. But - my folks were Navy (met in the Navy, mom was honorably discharged, because that is what happened in those days.) Also - I married a Marine. (Her “Over your dead body” is not a figure of speech :^)
Plus, I have lived in Albuquerque since 2003, and worked for several govt contractors. Spent a bit of time on a couple of bases plus been on a couple of weapons research facilities (WSMR, Yuma - in June - joy). If you are a nerd in Albuquerque, it is basically impossible to not work with the military.
I have seen NCOs pull other’s chestnuts out of the fire. True story. Was on a SBIR gig to gather data to create a drone refueling system. Flight tests at Niagara AFB. Lear jet pretending to be an F-16. Tests were the Lear pretending to be refueled by a KC-135. They brought the boom within a couple of feet of the Lear. This was some serious piloting. Air Force test pilots - some of the best you will ever find. The boom hitting the Lear would have been a Bad Thing. I had a very fancy video recorder. Camera was on the Lear’s “dash”. I was on two flights. Never had two hours pass so fast.
Another team had a GPS system - but forgot to be able to set it up for military precision. Panic ensued. A Sgt mentioned his brother, another Sgt, had the clearance and the majic incantations. Saved the GPS team’s ass. We are talking a $1Mill project just for the data.
Whenever I am on a base, everybody is “Sir” or “Ma’am”. NCOs let it slide because I am a civilian. Also, “I know I am not supposed to call you Sir, Sir” works. Don’t want to call a Senior Master Sgt just “Sgt”.
I was pretty aggressive in High School - football, wrestling, etc. I probably would have gone Marines or Army. As it was, nobody mentioned the intelligence branches - a logical place - they care about brains.
+dchisholm
Which branch were you?
U.S. Air Force communications officer, 1975 - 1981.
In Sept 1969 I started college and set aside a 2S student deferment to pursue a commission through the ROTC program. I expected that would include a Southeast Asia tour at some point. By the time I stood to receive the President’s commission in June 1973, the U.S. was beating feet out of SE Asia and drastically reducing military size. The Air Force didn’t have manning slots for all the people enrolled in commissioning programs. I took 18 months to make my first attempt at grad school, and eventually spent 6 years behind desks doing various headquarters-support jobs.
Dale
I don’t doubt that!
One of my most prominent memories from years in the Air Force was one ride as a passenger on a KC-135. I also gained an appreciation for some of that “serious piloting” when the boom operator let me watch over his shoulder while refueling a B-52. Later, several of us crammed into the boomer’s pod to take in the scenery when the flight path followed the Grand Canyon.
Like you, most of my interesting “military experiences” came after I left service and was working for defense contractors. It’s especially sobering to realize that some GI may be putting his life may on the line, trusting in some design decision you made. Occasionally you really DO remember back to some difficult design problem such as selecting an output capacitor, and hoping that what went into the final version is really up to the performance specs. (Well, at least I had those thoughts a few times.)
Dale
What you don’t know is that they may work perfectly fine when mostly new.
20 years later, they catch on fire when power is applied; and they make a horrid stench when in the box sent back for re-work.
I can recomand you this nice web tool from Kemet :
http://ksim.kemet.com/
It allows to compute a lot of parameters with curves depending of frequency, voltage, …
That’s nifty too, the Kemet version of the Murata sim I linked above
http://ds.murata.co.jp/simsurfing/mlcc.html?lcid=en-us
Any MLCC capacitor will have adequate ESR for your application. You are not focusing on the most important spec – minimum capacitance. ALL ceramic capacitors in this size/capacitance have a tolerance and a capacitance derating with voltage. You should use any 50 V 2.2 uF capacitor of X5R or X7R dielectric. It will meet the 1 uF minimum. It will also meet the 500 milliohm maximum ESR.
I did a little checking, and with the X&R or X%R dielectrics, a value of 1.2 uF or above is fine unless it will get hot in the circuit. 1.5uF is a sure thing…
Lol… Watch out holding the shift key when embedding digits between letters. Different international keyboards will map different symbols to the shift-digit combinations. For clarity you mean “X7R” and “X5R” respectively, right?
I believe you will find that just about any multilayer Ceramic Capacitor (MLCC) will be orders of magnitude better than this. It will be hard to spot in many data sheets because they are generally so good it’s not a consideration. You can calculate it from the Q factor of the part. A bigger concern is peak current rating, also generally poorly specified.
Why aren’t you using the reference design part? If you don’t understand the problem well enough to specify the parts yourself, this is the route you should go. You should also slavishly follow the layout recommendations if you don’t understand the requirements. If you didn’t, there’s a good chance that the part will not matter.
Oz
The OP is long gone. And it’s better that way :-0
Thanks to everybody who joined this topic.
I presented the question to my students (still more than a year away from graduating). The first one got the solution within less than 30 seconds.
They had a lot of fun with the comments afterward.
This topic was automatically closed 90 days after the last reply. New replies are no longer allowed.