59
votes
Why does Samsung include useless capacitors?
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:
...
- 1,216
48
votes
Why does Samsung include useless capacitors?
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 ...
- 84.8k
34
votes
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Why use two 0.1 µF capacitors in parallel?
C2 is used to decouple pin 28 and C3 is used to decouple pin 22 (or vice versa): -
See also the Allegro data sheet for the A4988 driver; it shows the capacitors as C7 and C9: -
- 465k
25
votes
Why does Samsung include useless capacitors?
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 ...
- 4,478
25
votes
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How do capacitors stop voltage spikes?
The capacitor is not there to absorb voltage spikes. The purpose of the capacitor is to prevent the short-term variations in the load current from becoming voltage spikes. $$\Delta V = \frac{\Delta Q}{...
- 175k
23
votes
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More Vdd than Vss Pins
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 ...
- 7,717
23
votes
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Decoupling Capacitors: What happens to the DC on the cap once noise is introduced and it shorts?
The capacitor does not "short out", it has charged up to a constant voltage by storing energy as electrical charge, and if something external tries to change the voltage over the capacitor, it means ...
- 159k
22
votes
Why use two 0.1 µF capacitors in parallel?
It is normal to use one de-coupling capacitor for each power pin.
Now you could place these capacitors all over the place in the schematic, but it is easier (and has become a sort of convention) to ...
- 14.5k
21
votes
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How to chose the right decoupling/bypass capacitor variant for opAmp power rails?
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 ...
- 1,299
21
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Super Duper Vdd stiffening required on 555 timer, what is the best way?
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 ...
- 407k
20
votes
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Decoupling cap routing on a 4 layer PCB
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 ...
- 56.9k
20
votes
DC bias of electrolytic capacitor
Capacitance variation with DC bias for aluminum electrolytic capacitors is insignificant. The following graph is a 3300 uF, 63 V Nichicon aluminum electrolytic capacitor. Data is from a HP4194A ...
- 10.3k
19
votes
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bypassing vs. decoupling capacitors
Yes, decoupling capacitor and bypass capacitor 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 ...
- 314k
19
votes
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PCB routing: isolate through-hole pins to force routing through decoupling capacitors?
The truth of the matter is that it doesn't really matter if the current "hits" the capacitor before the pin of the IC or not. This has long been debated and recent studies have suggested ...
- 21.4k
18
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How do smaller capacitors filter out higher frequencies than larger values?
If practical capacitors were purely capacitive, then indeed, a larger capacitor would do an even better (or at least "as good") job of filtering high frequencies as a smaller value one.
But ...
- 33.6k
18
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Why are PC motherboards covered with many large capacitors?
I drew boxes around all of the things that are clearly (even at this very low resolution) DC to DC converters:
As you can see, nearly all of the electrolytics are associated with a DC-DC converter. ...
- 17.6k
17
votes
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What's the purpose of an array of same VALUE capacitors?
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 ...
- 169k
17
votes
Is there a formula to determine the size of decoupling capacitors?
Remember decoupling has several purposes.
On a load which draws transient, spiky currents like a CPU, decoupling caps store energy locally and close to the load, so it is available quickly (ie, with ...
- 79.5k
17
votes
Why does Samsung include useless capacitors?
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 ...
- 871
17
votes
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Why might one of these decoupling capacitor schematics also include an inductor and the other not?
Some parts of the circuit are usually more sensitive to power supply noise than others (especially high frequency noise), and some parts of the circuit may also inject different amounts and ...
- 79.5k
17
votes
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What is the use case for a tantalum capacitor?
Let’s start with some of the advantages of tantalum capacitors
They have relatively good stability across frequency, voltage, and temperature range compared to electrolytic and ceramic capacitors
...
- 2,364
14
votes
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ATmega328 decoupling caps: are they in right position?
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 ...
- 314k
14
votes
Super Duper Vdd stiffening required on 555 timer, what is the best way?
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 ...
- 31.6k
14
votes
How do capacitors stop voltage spikes?
The capacitor and power source appear in parallel in the schematic, but the schematic doesn't show parasitic inductance and resistance in the wiring. In reality the circuit might look more like this:
...
- 39k
13
votes
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Does a MAX485 need decoupling capacitors?
Yes. All almost ICs need decoupling capacitors. Devices such as these '485 drivers especially need them due to the current surges the device experiences when switching the signal states due to the low ...
- 57.5k
13
votes
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Understanding STM32 datasheet regarding decoupling capacitors
They are referring to the total number of capacitors needed.
ST has a useful document: "AN4325 - Getting started with STM32F030xx and STM32F070xx series hardware development"
Inside, it is a bit ...
- 17k
13
votes
Which of these layouts for decoupling capacitors attached to an IC is wrong?
Given what you've shown, you want to use your first option - vias to the GND plane and no trace.
Problem with option 2 (right most) is the loop & inductance formed by the trace between the cap ...
- 10.9k
12
votes
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Why decoupling capacitors used for power rails should be very close to the IC pins?
The ICs contain fast switching transistors generating RF signals. As you know all electrical signals travel in loops. For these ICs the loop is through the power supply pins.
The decoupling caps form ...
- 81k
12
votes
Why does Samsung include useless capacitors?
Under high frequency conditions, a metal plane is not a continuous, equipotential conductor, but instead acts as a resonant structure due to distributed R and L, as well as geometry, i.e. fringing ...
- 1,240
12
votes
How to calculate values for decoupling capacitors
Basically you want something close enough to the pin that at the edge rates in play the bounce is not too bad, and then something further away with (possibly) enough ESR to damp everything to keep the ...
- 17.6k
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