Questions tagged [decoupling-capacitor]

A capacitor, usually ceramic, used to provide instantaneous energy to a local circuit.

Due to parasitic elements (inductance, resistance, etc.) a sudden current draw by a component (like an amplifier, or digital logic IC) often cannot be satisfied without disturbing the power rail feeding the bus.

A decoupling capacitor, placed as close as possible to the power and return pins of the circuit in question, provide local energy storage and can provide the instantaneous energy needed without causing a bus disturbance. Decoupling capacitors tend to be ceramic due to their high-frequency performance and low ESR.

The voltage disturbances caused by sudden draw can lead to latch-up and other malfunctions in integrated circuits, and are also a source of electromagnetic interference (EMI).

Decoupling capacitors are also referred to as bypass capacitors.

References

Wikipedia article on decoupling capacitors.
Decoupling caps, PCB layout

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Decoupling caps, PCB layout

I guess I've been somewhat ignorant when it comes to the finer details of pcb layout. Lately I've read a couple of books that try their best to lead me on the straight and narrow. Here is a couple of examples of a recent board of mine, and I have…
morten
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What is a decoupling capacitor and how do I know if I need one?

What is a decoupling capacitor (or smoothing capacitor as referred to in the link below)? How do I know if I need one and if so, what size and where it needs to go? This question mentions many chips needing one between VCC and GND; how do I know if…
Redwood
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Why does Samsung include useless capacitors?

I do component-level repair of tablet mainboards, and I have seen this puzzling situation on two different models of Samsung tablet mainboards so far (SM-T210, SM-T818A). There are ceramic chip capacitors on the PCB that are clearly connected to the…
Crash Gordon
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Decoupling capacitors: what size and how many?

Lots of chips nowadays require smoothing capacitors between VCC and GND for proper function. Given that my projects run at all sorts of different voltage and current levels, I was wondering if anyone had any rules of thumb for a) how many and b)…
jeremy
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What's the use of a decoupling capacitor near a reservoir capacitor?

I've seen some circuits where a decoupling capacitor is used as well as a reservoir capacitor, like this (C4 and C5): I've read about decoupling capacitors and for me it looks as if they are meant to remove small fluctuations in the supply voltage.…
user17592
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Can I replace all electrolytic capacitors with ceramic?

I am designing the power supply circuit for a system that needs several supplies, my questions are: Is it possible to replace all electrolytic caps (Mostly 100uF) by ceramic ones? What are the limitations of ceramic? Should I use a 2x voltage rating…
Abdella
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Why aren't decoupling caps built into the IC or IC package?

The title is probably good enough, but I've always wondered why decoupling caps aren't built into the chip or at least the IC packaging?
kenny
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Are decoupling capacitors needed with battery power?

Currently I run all my gadgets from batteries and don't use decoupling capacitors. Are they generally needed/useful when drawing energy from a battery?
Mr. Hedgehog
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How to place decoupling capacitor in four-layer PCB?

I searched a technology document about placement of decoupling capacitors and the main idea is shown in the following picture: I think it is reasonable but do I have to put the decoupling capacitor and MCU in the same layer? it is not convenient for…
oilpig
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Why does ST recommend 100 nF decoupling capacitors for a 72 MHz MCU? (And not 10 nF.)

I've been reading about decoupling capacitors, and I can't seem to understand why ST recommends 100 nF decoupling capacitors on a 72 MHz ARM microcontroller. Usually 100 nF decoupling capacitors are only effective up to about 20-40 MHz due to…
Mike
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"two bypass/decoupling capacitors" rule?

I found many discussions on bypass capacitors and their purpose. Usually, they come as a pair of 0.1uF and 10uF. Why does it have to be a pair? Does anyone have a good reference to a paper or an article, or could provide a good explanation? I wish…
Nazar
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Do chips really need multiple values of decoupling capacitor in the same packages?

A similar question is asked here: "two bypass/decoupling capacitors" rule? But that question was about parallel bypass capacitors without mentioning package size (but the answers mostly assumed paralleling parts with different package sizes), while…
Rocketmagnet
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Why connect capacitors to motor body?

So I've found a motor circuit which looks like this: Since many users here believe that my hand-drawn circuit schematics are in fact pictures of flying spaghetti monster, I'll also provide a written description: There are two input lines marked +…
AndrejaKo
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Why use two 0.1 µF capacitors in parallel?

Below is the schematic of the Pololu A4988 driver board: There are three capacitors on the motor power input. I can understand why engineers decided to use separate 4.7 µF with larger size (1206, 0.1 µF are either 0805 or 0402): because physically…
Zhenek
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Decoupling capacitors on the bottom layer?

I'm using 0.01 uF decoupling capacitors in a 0805 package , on each V cc /GND pair of my CPLDs . So, around eight capacitors in total). I find it a bit easier to route the board if the decoupling capacitors are placed on the bottom layer and…
Saad
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