What type of capacitor is this? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 31, 2020, 01:47:52 am
content: Luckily do I have a lot of info about the C6 capacitor but still do it confuse me, because it does not look like an electrolytic capacitor.It's a SMD, the neighboring component is properly 1206, the circuit is about 2GHz and the cap is connected to power in.Values C6, 10uF 10V polarized.

author: amyk
author_rank: Super Contributor
timestamp: October 31, 2020, 01:53:24 am
content: It's a big MLCC next to a small one.

author: helius
author_rank: Super Contributor
timestamp: October 31, 2020, 01:53:45 am
content: My suspicion is that the schematic was drawn with a solid SMD tantalum but the assembler used a MLCC instead. The MLCC is not polarized, although a tantalum is and would need to be placed with correct polarity.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 31, 2020, 02:15:53 am
content: C5 is a 100nF.Okay so it does still not matter if polarized or not when it's an HF circuit?Is it best to use a MLCC X7R and C0G?Can I just ignore polarization anywhere where I can find a MLCC at the same capacity?Found 10uF:https://www.mouser.dk/ProductDetail/KEMET/C1206C106J8RACTU?qs=guDyKOyRtV0XXPO97OuO6w%3D%3DThanks to you both! :-)

author: Kleinstein
author_rank: Super Contributor
timestamp: October 31, 2020, 08:30:56 am
content: Using a non polarized cap where a polarized cap is planed is not a problem by itself. However the electrolytic caps also usually have additional ESR. Some applications (especially LDOs) need the ESR - so there are a few cases where one can not use a MLCC instead of an electrolytic cap or would have to add a series resistor. Some LDO's are OK with MLCC, but not all.X7R dielectric allows for high capacity in MLCC , but it also has a high temperature dependence and is nonlinear and with added loss (still less than electrolytic). C0G type caps are much closer to an ideal capacitor, more like comparable to good film types - however the capacity is much lower (e.g. rarely larger than 100 nF and this is already large).X7R are used for supply decoupling and filtering, where the exact value and loss does not matter. C0G are more for signal filtering, timing and other demanding tasks. Classical is was for something like < 5 nF, only newer MLCCs made also slightly larger values available.

author: FriedMule
author_rank: Frequent Contributor
timestamp: October 31, 2020, 12:23:32 pm
content: Okay thank you!! But what would you recommend for 10u 10V at around 2GHz?

author: helius
author_rank: Super Contributor
timestamp: October 31, 2020, 02:24:18 pm
content: Note that ceramics like X7R have low ESR, lower than an electrolytic, but highdielectric loss, which is not "loss of energy" but ofcapacitance! A 1 uF X7R operated at 50V DC bias exhibits much less of its capacitance from the nominal value. This requires its own type of derating to compensate for.

author: Gyro
author_rank: Super Contributor
timestamp: October 31, 2020, 02:39:00 pm
content: Quote from: helius on October 31, 2020, 02:24:18 pmProbably best not to refer to that as "dielectric loss", which is already a well defined parameter for capacitors. I believe what you are referring to is normally referred to as 'voltage coefficient' (which can apply both to the value of capacitors and resistors).

author: Kleinstein
author_rank: Super Contributor
timestamp: October 31, 2020, 02:43:31 pm
content: The X7R dielectric also have high dielectric loss, like in energy loss. If they see significant ripple current and voltage they will get warm. In most applications however there is only a low ripple voltage and the loss of capacitance can be a real problem. The details depend on the specific type and size, but expect a 10 µF 16 V MLCC to have more like 1/2 the capacitance at 5 V.So the choice of capacitor may be a 10 µV 16 V tantalum polarized cap or a 22 µF 10 or 16 V MLCC (X7R). For 2 GHz it does not make a lot of difference if the cap is 100 nF or 10 µF - both look more like a few nH of inductance in the GHz range.

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 01, 2020, 08:50:59 am
content: Quote from: FriedMule on October 31, 2020, 12:23:32 pmThrere are still low-frequency things doing inthe chip too, so it needs a bulc (low-frequency) cap. There is 0.1 uF for higher frequencies in parallel.

author: FriedMule
author_rank: Frequent Contributor
timestamp: November 09, 2020, 11:47:09 am
content: You are great, I am now thinking of using these two capacitors. Are they okay?:100nF:https://www.mouser.dk/ProductDetail/KEMET/C1206C104J4GACTU?qs=w3%252Bcv6Flocrt%2FXd4jvCPKw%3D%3D10uF:https://www.mouser.dk/ProductDetail/KEMET/C1206C106J8RACTU?qs=guDyKOyRtV0XXPO97OuO6w==

author: David Hess
author_rank: Super Contributor
timestamp: November 09, 2020, 12:24:22 pm
content: Quote from: Kleinstein on October 31, 2020, 02:43:31 pmI have measured a lot of X7R and Z5U capacitors over the years and dielectric loss was always so low that the results were questionable. Only film and C0G/NP0 capacitors were better.

author: Infrared_Fred
author_rank: Regular Contributor
timestamp: November 09, 2020, 04:06:43 pm
content: Quote from: Kleinstein on October 31, 2020, 08:30:56 amDepending on the circuit, if this a bulk capacitor next to a ceramic capacitor, it may be important for the circuit to use a capacitor with some ESR to prevent high frequency oscillations on the power supply caused by inductance in the supply lines. To add ESR to a ceramic a small series resistor could be used but a tantalum capacitor might be easier.Note: I do not have much experience in this regard myself, but I have heard about this type of configuration sometimes being problematic.

author: David Hess
author_rank: Super Contributor
timestamp: November 09, 2020, 04:34:58 pm
content: Quote from: An Anoymous Geek on November 09, 2020, 04:06:43 pmSuppressing resonance in the power distribution network can be one function however more commonly the pole formed by the output resistance of the regulator and the output capacitance can cause oscillation of the regulators negative feedback loop from the added phase shift. The higher output resistance of low dropout common source/emitter regulators and low quiescent current regulators make them even more sensitive to output capacitor ESR.The solutions are to either increase the capacitance enough to increase the gain margin by limiting bandwidth, or add a zero in series with output capacitor to provide phase lead which is where the capacitor's ESR comes in. The later is sometimes done inside the regulator with a series resistor or other structure.Given the above, replacing a bulk output tantalum or electrolytic capacitor with a ceramic part is usually a mistake, and the example shown seems to indicate this because the smaller decoupling capacitor was kept or even existed in the first place.