BOM prob. ESR Output Capacitor - TPS5560200 - Page 1
Forum section: electronics / beginners

author: Docara
author_rank: Regular Contributor
timestamp: November 26, 2019, 03:16:09 pm
content: HiI'm following primarily TIs workbench software for a 13.2V(nom) to 3.8V converter. The output is going into a LDO (200mA DO) Linear for the final 3.3V. (thanks Dave for your 1cent reg series check out AP2127K-3.3)The Schematic states a 47uF 2.0mOhm ESR output multiple layer ceramic capacitor is required, I will be needing 30-40 of the little f**kers and I'm getting hit for between £0.41 and £1.00 EACH even on LCSC!! Even if I bang in a couple of lower values I'm getting stungDo I really need an ESR here, if yes what is the importance of ESR in this location, why such a low value and what alternatives could I use - I don't really know when to use different types of caps in situations like these (Dave if your watchin' mate hint hint)Lastly, for completeness, on the data sheet of the AP212 the input and output caps are a 1uF.Thanks

author: thinkfat
author_rank: Unknown
timestamp: November 26, 2019, 03:40:57 pm
content: How about just putting two or three of these:https://lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_SAMSUNG_CL10A226MQ8NRNC_22uF-226-20-6-3V_C59461.htmlIf you're really concerned about ESR. Normally, ESR for a MLCC capacitor is a minor issue. For very high switching frequencies, ESL is maybe more important.

author: Docara
author_rank: Regular Contributor
timestamp: November 26, 2019, 04:29:00 pm
content: Hi thinkfat,In answer to your question, it is because I do not know enough about the implications or reasons for using an ESR Cap in a given situation.Hence why I was asking why you need an ESR cap here.I prefer to put caps in with a higher voltage head room than 2V ish, so I have been looking at the 10-25V ranges

author: thinkfat
author_rank: Unknown
timestamp: November 26, 2019, 05:10:59 pm
content: Not sure what you think an "ESR Cap" is. ESR -> Effective Series Resistance, it's a parameter of every capacitor, so the design asks for a 47µF capacitor with very low ESR.You can use any MLCC capacitor for that, usually their ESR is in the single-digit milli-Ohm range. If you think the ESR is not low enough, just put a couple of them in parallel.10V will be fine, I'm sure you'll find something on LCSC for little money.They get expensive at higher capacities and smaller footprint size, but 22µF is available in 0805 size for less than 10 cents, just put three of them.

author: Docara
author_rank: Regular Contributor
timestamp: November 26, 2019, 05:24:06 pm
content: I don't know what ESR is or how it impacts a circuit that's why I have posted a question here

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 26, 2019, 09:56:38 pm
content: Who says you need 30-40 of them? Like, in one design?If that's across a build of as much quantity, suck it up, you're spending a few bucks per board, that's normal?Tim

author: Docara
author_rank: Regular Contributor
timestamp: November 27, 2019, 09:15:19 am
content: T3sl4co1lI asked a perfectly reasonable question in the beginners section of this forum.For you to tell me to "suck it up......that's normal" is not helpful! You know nothing of the circumstances behind the question.In the post immediately before yours it stated "I don't know what ESR is or how it impacts a circuit that's why I have posted a question here", so if you had answered my question with a nice explanation of ESR caps and then told me to 'suck it up' that would be a different matter.

author: thinkfat
author_rank: Unknown
timestamp: November 27, 2019, 09:45:28 am
content: Alright, but maybe you could put a little effort into it yourself? Like, google what ESR means when talking about capacitors? Spoonfeeding is not something people like doing, even in this section of the forum...

author: Docara
author_rank: Regular Contributor
timestamp: November 27, 2019, 03:43:06 pm
content: Hi bothHow about giving me a bit of credit! I'm far from a spotty nosed little teenager looking for homework answers.I wasn't expected to be "spoon-fed" - I didn't understand the information that I did find. So guess what I did, I asked advice from people who know better than me only to be slammed down because I had the audacity to ask.Let me reiterate my initial question:-"Do I really need an ESR here, if yes what is the importance of ESR in this location, why such a low value and what alternatives could I use - I don't really know when to use different types of caps in situations like these"So which part of this statement infers I didn't try to find informationThe recommended capacitors stated in TI's Workbench are obsolete or not for new designs. There is a large range of ESR values stated as alternatives. The alternatives Ihavefound don't state an ESR value just 'low ESR" but then again if I didn't do any research how would I know this?Why can't you people just answer questions instead if pissing from the high ground

author: thinkfat
author_rank: Unknown
timestamp: November 27, 2019, 05:31:27 pm
content: Let's put it like this: if, after doing all this research, you still don't know that there is no such thing "ESR Cap", it clearly wasn't enough :-)

author: MagicSmoker
author_rank: Super Contributor
timestamp: November 27, 2019, 05:39:10 pm
content: I'm inclined to side with CJay here, but to answer the OP's question, anyway... ESR is the lumped sum of the actual ohmic resistance of the conductors, plates, etc, and the equivalent resistance from dielectric losses; it's not atypeof capacitor, it's a property of them. Sometimes the cap manufacture gives the ESR, but sometimes they are a bit more sneaky and give a spec for "dissipation factor" (either in percent or the tangent of the loss angle). In either case, D.F. is the ratio of ESR over capacitive reactance and is heavily influenced by the type of dielectric, clocking in around 0.1-0.2% for both NP0/C0G ceramic and polypropylene film types, 2% for polyester/PET types, and 3% for Hi-K ceramic types (X7R, Y5U, etc.)So for example, a 1uF NP0 MLCC with a D.F. of 0.15% will have a capacitive reactance at 100kHz of 1.59 ohms and an ESR of 2.39 milliohms, but if the dielectric is X7R then the ESR will jump to 47.8 milliohms.Since ESR behaves exactly like a resistor it leads to heating of the capacitor and produces ripple when fed with alternating or pulsating current (like the output of a switchmode converter), hence two good reasons to minimize it right there.ESR isn't always bad, however, but why that is the case I leave it to those interested to search for themselves.