 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Microcontroller and PC projects : Replacing Tantalum With MMLC Caps
| Author | Message | ||||
Geoffg Guru  Joined: 06/06/2011 Location: AustraliaPosts: 3165 |
Most of us have heard of multilayer ceramic capacitors (MLCC) and I always thought of them as a superior replacement for tantalum caps. This particularly applied to the capacitor connected to the Vcap pin on the PIC32 (used to stabilise its internal 1.8V regulator). But MLCC caps have some nightmare characteristics. I found this article very interesting (and disturbing): http://www.eetimes.com/author.asp?section_id=30&doc_id=1330877& Geoff Geoff Graham - http://geoffg.net |
||||
Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9063 |
I guess it comes down to a case of "If it works...." I do remember the pros and cons of MLC's being discussed in the forums recently. Also, exactly how accurate is the article? It says all the right things, and mentions the guy calling the fella back to confirm it, but how much of that is truth, and how much is just scaremongering? In the 250-odd MM PCB's I have built so far(MM1/MM2/E64/E100), NOT ONE has failed to start using the standard recommendation of 10uF X5R, and I use 6v3 type too, which, going by that chart, should have such a low capacitance at 3v3 as to be useless and in the event, prevent the MM from starting due to a 'Dirty' 1v8 core voltage. Either that, or start but run very sporadically and cause lots of errors due to bad core voltage stability. I have never seen this in the plethora of MM's I have had anything to do with so far. I hear what they are saying, but at the end of the day......... What are other members thoughts and opinions? Smoke makes things work. When the smoke gets out, it stops! |
||||
| Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3165 |
Your 6.3V MLCC on Vcap is actually operating at 1.8V so it is not all that bad. I think that the big problem is that these capacitance vs voltage graphs are almost impossible to find for the caps that we are buying. Also, I reckon that Microchip has built a lot of slack into their recommendation for Vcap so that helps. Geoff P.S. > the 250-odd MM PCB's I have built Wow! Impressive. Geoff Graham - http://geoffg.net |
||||
| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2289 |
herein lies a common error - they [MLCC] are an alternative, a possible replacement in certain applications, but not something that can be considered inferior OR superior. just a component with a different set of specifications. the author of the article did not observe any unexpected behaviour: a component (tantalum capacitor) connected backwards failed. a Y5V 1uF capacitor with a +22/-82% tolerance rating displayed a 0.3uF capacitance under certain conditions. a table of data from wikipaedia did not reveal the full picture. these are all quite normal things. when selecting components it is necessary to fully read the datasheets and understand all aspects of the operating environment and the resultant effects upon component performance. i worked in production and test engineering for many years, and can confirm it is hard work. you assume nothing, test everything. in mass manufactured products, components have to be specified down to the very last letter of a component manufacturer's part number. the greatest enemies are counterfeits and unauthorized substitutions, and i have had to deal with the fallout of both. cheers, rob :-) |
||||
| WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
As many of you know, I am a big fan of MLCCs for the MicroMites; rather than using Tantalums. As with Grogster; I have NEVER had an issue with MLCCs in any of the PCBs I have assembled for the many micrometer.org customers. I have always used 10uF MLCCs for vCap (apart from the very early days of beta testing back in March/April 2014). Even in PCBs that accommodate thru hole Tants, I have always used a 1206/1210 SMD cap. When I worked in a service department for electronic products, the most common fault was failed capacitors. If you look at data-sheets, many are specified at just a few hundred hours of service life!!  Is this really appropriate; especially for PSUs that need near 24/7 on time?MLCC will always get my vote in MM circuits . . . . WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
||||
redrok Senior Member  Joined: 15/09/2014 Location: United StatesPosts: 209 |
Hi All; Capacitors varying with voltage is not all bad. It can be useful!! See this low frequency VFO or variable frequency oscillator: Multilayer capacitor doubles as varactor Its about halfway down the PDF. This actually works pretty well. Notice this is from 2003. redrok |
||||
bigmik Guru Joined: 20/06/2011 Location: AustraliaPosts: 2870 |
Hi All, An interesting read and as noted, on that scale a 10uf rated at 6v3 and running at 1v8 would probably have a very low capacitance. It has been proven that they work extremely well so I wouldn't be too worried about that. Although personally I still use 47uF 6v3 Tantalum for my VCaps.. Why?? Well simply I have at least 100 of them still in stock. I will reappraise that situation when it comes time to renew my stocks (based on current sales I reckon around 2020). I am, of course, concerned about people reverse fitting them.. Kind Regards, Mick Mick's uMite Stuff can be found >>> HERE (Kindly hosted by Dontronics) <<< |
||||
 Print this page |
