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73

100 µF is really pushing the limit for ceramic caps. If your voltages are low, as a few volts to 10 or maybe 20 volts, then paralleling multiple ceramics may be reasonable. High capacitance ceramic caps have their own set of advantages and disadvantages. The advantages are much lower equivalent series resistance and therefore much higher ripple ...


57

There are four comments on this reddit thread that may be on to something: By silver_pc: could it be a form of 'paper towns' on maps - AKA fictitious entry to identify direct copies? By toybuilder: Not that they are necessarily doing this, but I've heard it said that mass manufacturers will keep removing capacitors until their product stop ...


53

The most likely reason why that is done is because, in real life, capacitors do not have infinite bandwidth. Generally, the higher the capacitance of the capacitor, the less it will be able to react to high frequencies, while small-valued capacitors react better to higher frequencies, as seen in the graph below. Using two different-valued capacitors together ...


42

At first I thought it might be purely mechanical, maybe a way to keep people from bumping the BGA part off the board, but the other two pictures suggest that it is not as the caps are surrounded by many other parts. There is some commonality between all three designs: 1) They are placed next to circuits. One of them is a boost\buck DC to DC circuit. 2) They ...


29

As you say, a decoupling cap and a power supply bulk reservoir cap serve two different purposes. You are correct in that the decoupling cap needs to be physically close to the consumer of the power it is decoupling. The bulk cap can be anywhere on the power net since it deals with low frequency currents. However, the incorrect assumption you are making is ...


25

Some linear regulators are not stable when the ESR of the output capacitor is too low. This can result in oscillations when high-Q ceramic capcitors are used at the output. The designer may have been concerned this issue applied to the regulator used, and added the series resistor as a solution. Edit After reviewing the linked datasheet, this is almost ...


23

http://www.ti.com/lit/an/scba007a/scba007a.pdf You'll see the big capacitor referred to a "bank" or "bulk" capacitors. The smaller ones are of course also "bypass" capacitors. The basic idea is that, in the real world, the parasitics of a capacitor aren't ideal. Your "bank" capacitor will help for transient power draw (changes in real current change) but, ...


23

As a chip maker, it's easy for me to explain the cause of the imbalance. It's that there are several different rings of VDD in the IC for different purposes, but only a single ground. The different VDD rings can be in different voltages, but the ground is always at zero volts. So for the ground, there is a solid copper rectangle in the leadframe (that's ...


22

When two or more decoupling capacitors of different values are used in parallel, it is necessary consider the parallel resonance that occours between the two networks. Clayton Paul described this phenomena. Consider a parallel coupling of capacitors C1, C2, with different values and C1>>C2 with parasitic L1 and L2 about the same L1=L2 (figure 1.A). We ...


21

Three things you should note: 1) Most bypass recommendations in datasheets and application notes are fairly random in my opinion. You may easily be a better engineer than the person who wrote the application note :-). A better datasheet would talk about how low an impedance you as a board designer should provide and to what frequency. I wrote about this ...


21

Your measured short-term stability is about +/-0.01%, which isn't bad for an uncompensated RC timer. You can improve it by using low temperature coefficient resistors and capacitors in the timing circuit, maybe by bypassing pin 5 to ground, by isolating the circuit thermally and electrically, in the extreme controlling the temperature in an oven, powering ...


20

This is a complex problem to analyze and many parts of it only are important when you run into a problem at a specific frequency on a specific product that noone knows how to fix. While this answer is sort of a side point, it addresses some assumptions. We are talking about bypass caps which only concern is high frequency noise and not large power draws. ...


20

Yes, you need decoupling caps. Between the Vcc and GND pins of the ATtiny, close to the ATtiny make it approximately 100nF And it doesn't hurt to have one close to any other "high current" switching components, like near the LED. Don't decouple the LED itself, decouple the LED with its series transistor. Say another 100 - 220nF. simulate this circuit &...


20

I wouldn't think of a decoupling capacitor as a filter in the way you describe. Like an RC filter like this, where the source of the noise is the power supply and your "decoupling" capacitors are helping to filter that out before it reaches your chip. simulate this circuit – Schematic created using CircuitLab It's not keeping noise from getting to ...


19

It actually does not matter too much, according to Henry Ott's book on EMC. Proximity, trace length, and loop size matter more. If the IC and cap are on different sides of the PCB, placing both vias along the edge of the capacitor pad side (rather than the ends) so they are closer also reduces inductance since magnetic fields of opposite currents in the via ...


18

There are a couple of reasons not to switch a design from electrolytics to ceramics that haven't been mentioned yet: Some linear regulator designs require the higher ESR of the electrolytic on their output capacitor to maintain stability. Ceramics are less robust than electrolytics when subjected to board flexure. Especially in the large sizes, say 1206 and ...


18

Capacitors eventually stop behaving like capacitors at high frequencies and exhibit resistive and inductive effects. The 100pF capacitor filters high frequencies that the 100nF capacitor could not. This is shown clearly on the diagram below which shows the impedance (Red) of a 100nF capacitor and a 100pF capacitor (Light Grey top curve) versus Frequency. ...


18

Drill a small hole that will allow you to simply run a free thin piece of wire from the ground plane on the opposite side of the board to the capacitor. Stripped wire-wrap wire works well. It's 30 AWG, so the hole that you drill can be very small. Use a Dremel tool in a drill press if you have such available - I routinely drill #78 holes reliably without ...


18

That might be a feed trough capacitor, it's not clear from the pictures. Feed through capacitors are usually used in RF circuits and are designed to be connected to ground on the edges and have a center pad for the other terminal of the capacitor. EDIT The new picture reveals no pad under the capacitor so it's not a feed through capacitor but I'm leaving ...


17

If you count the power pins on the IC, and the supply decoupling caps of the same value, you'll probably find a 1:1 correspondence. This indicates you are expected to place one per power pin, as close as practical to the pin, to minimise the effects of trace inductance.


16

I think you can most likely add a little fly wire from the existing GND via (or a closer one above) to the capacitor. If you're having problems, do what Dwayne suggests and drill a hole and scrape the resist off, but you've got little to lose in trying the easy way first, especially if this op-amp is not directly handling the high frequency signals.


16

Possibly a crazy thought, but it could be process control. The caps all are near large metal objects, which are can prevent the board heating properly during reflow. The double grounded caps are larger than their neighbours, and with 2 connections to the ground plane make them the most likely candidates to not solder properly if your pushing the limits of ...


15

Pursuant to OP's derating questions, and further to Olin's fine answer: IPC-9592A (which is a standard for high-reliability power conversion devices) cites the following derating guidelines: Fixed ceramic MLCCs: DC voltage <= 80% of manufacturer's rating Temperature: Minimum 10°C below manufacturer's rating Size: Sizes larger than 1210 not recommended ...


15

Given how close the nearest ground region is, you probably don't need to use any wire or drill holes. In the picture below, the points in the green circle are both Ground, in which case all you need do is scratch off the solder mask nearby and add a solder bridge. This will create a nice large (low inductance!) connection between the C18 ground pad and the ...


14

Yes, decoupling capacitor and bypass capapcitor are the same thing. These refer to a capacitor located physically close to something drawing power. The capacitor holds the local voltage up for the short time until the current feed can catch up. Due to inevitable inductance of longer lines back to the power supply, the current in these lines takes a little ...


14

Use the first layout. There is no need to split the Vcc feeds like that. Other issues: The ground connection to each cap is also important, in many cases even more important, than the power connection. You haven't show that at all. Getting that right should be your first concern. There should be a short trace directly back to the nearest ground pin ...


14

I don't think you will ever get the accuracy and stability you want from a 555 timer. The pulse width is determined by the values of resistors and a capacitor, and the values of these elements will change with temperature and over time. For a precise pulse duration you should be looking at a crystal oscillator with a digital counter to generate the desired ...


13

Real capacitors have inductance and resistance. The objective of a bypass capacitor is to rapidly respond to current transients in order to maintain a stable voltage. The series inductance and resistance are counter to that goal. simulate this circuit – Schematic created using CircuitLab As the current through the capacitors increases, the voltage ...


13

Is that the inductance, Yes resistance Yes or maybe impedance of the PCB track Yes or wire Yes that affects the electric charge? hmm .. it affects the electric current, not so much the charge. The current from capacitor to decoupled device must meet as little "obstruction" as possible. Devices can have huge inrush currents when ...


13

There is a difference between op-amp decoupling and, for example, logic chips decoupling. The purpose of bypass capacitors is to provide sufficiently low impedance on power rails in the whole frequency range of the op-amp. Different types of op-amps have very different frequency range: Gain Bandwidth Product (in fact, it typically defines the bandwidth) ...


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