Tagged Questions

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

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0
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1answer
47 views

Decoupling Capacitor Value [duplicate]

I am taking 12V from Power card to my backplane card to use for Hard disks. I have been advised to put decaps of 330 uF on 12V supply. Can I use 220 uF or even lesser value. What is the criteria for ...
10
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2answers
228 views

Why does ST recommend 100nF decoupling caps for a 72MHz MCU? (And not 10nF)

I've been reading about decoupling caps, and I can't seem to understand why ST recommends 100nF decoupling caps on a 72MHz arm mcu. Usually 100nF decoupling caps are only effective up to about ...
2
votes
0answers
69 views

Optimal Capacitor Placement on DC/DC Convertor

I'm trying to decide on the best layout for caps on a DC/DC converter. Which of the following options (or another, unlisted option) is the best choice? GND Out plane with 5V Out going the opposite ...
10
votes
3answers
881 views

Parallel Capacitor Conundrum [duplicate]

I have recently taken on a project that involves improving a circuit and there is a couple of instances where there are two capacitors in parallel with each other. The values of these capacitors ...
1
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1answer
212 views

Decoupling Capacitor

For power pins of IC we add a decoupling capacitor, suppose a design misses the decoupling cap. Is there anything that can be done on layout to counter the missing decoupling capacitor? My first guess ...
0
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2answers
171 views

Using a shunt cap to create a delay - good idea? [closed]

simulate this circuit – Schematic created using CircuitLab C1 is a decoupling capacitor. If the input of U1 is experiencing undesired phase shift, can a decoupling capacitor correct the ...
1
vote
1answer
18 views

PCM4202 AGNDL/AGNDR connection

First, sorry if my english is not perfect. I have a question regarding AGNDL and AGNDR connectiof for PCM4202 . In the data sheet document ( figure 12, page 21) the decoupling caps are not connected ...
0
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2answers
70 views

Decoupling Capacitor - Multiple Vss pins

I'm about to start using a chip that has one positive and two ground connections - I've only used chips with one positive and one ground before. How should I attach the decoupling capacitor(s?) to ...
6
votes
2answers
196 views

Should I keep the decoupling capacitor's vias isolated from ground fills?

I'm finishing up a PCB layout which contains a 6.5 GHz ultra-wideband transceiver with a chip antenna, an ARM controller running at 72 MHz with a 12 MHz crystal, a 16 MHz SPI bus with 3 peripheral ...
7
votes
3answers
463 views

Deciding capacitor value to use in my circuit

I have a power source which supplies 1A at 5V. I am using a switching regulator which supplies 1.3A at 3.3V. The load requires a burst of 2A without reducing the voltage across it than 3.2 V for 477 ...
4
votes
2answers
210 views

Decoupling with multiple caps per pin. Which should be closest?

I have an Ultra Wide Band transceiver with an internal power amp. This PA has two input pins for Vdd. According to the manufacturer, each of these pins should be decoupled with three caps; 10p, ...
2
votes
1answer
135 views

Bypass/decoupling capacitor type choice [duplicate]

Having different types of capacitors (electrolytic, film, silicon, tantalum, etc.), which types would be the optimal choice for polar/non-polar pair in this common configuration: I understand the ...
0
votes
1answer
158 views

Decoupling a power supply

I'm building my first biped robot, using a Raspberry Pi as the brain. My problem is, I want to decouple the battery before I use it to power the Pi. The reason I want to decouple the battery is ...
1
vote
2answers
244 views

Op Amp Decoupling with a Virtual Ground

I'm designing a low-frequency op. amp. circuit that operates from a single 10V supply. I'm using a TLE2426 "rail-splitter" to generate a virtual ground, 5V above earth ground, which is used as a ...
1
vote
1answer
102 views

Review and question about AD9838 circuit

I have tried to come up with a schematic of using AD9838. I used the eval. board schematic and modified it to my needs. The eval. board schematic can be found on page 9 here: AD9838 eval. board ...
0
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1answer
317 views

Decoupling Arduino's power supply

I am building a replacement for dishwasher's controller that burned, using Arduino Leonardo. Arduino is powered through standard 9V AC/DC converter. Dishwasher uses quite large 220VAC electric pump ...
2
votes
1answer
116 views

Are there flaws in the reasoning behind the Zedboard bypass scheme?

There is an eval board for the Xilinx Zynq-7000 FPGA called the Zedboard. When you look at the board you will notice a very interesting pattern of bypass capacitors. The designer has a technical note ...
2
votes
1answer
187 views

Norton Equivalent of Capacitively Coupled LRC Circuit

The diagram below is a schematic representation of a microwave lumped element notch filter. The goal is to analyse the parallel LRC circuit and derive an expression for \$S_{21}(\omega)\$, where port ...
14
votes
3answers
1k views

Why need the capacitors be as close as possible to the device?

Just a simple question: what exactly stands behind the need for placing the capacitors as close as possible to the current consuming device's pins? Is that the inductance, resistance or maybe ...
10
votes
3answers
850 views

“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 ...
2
votes
4answers
168 views

When to use film capacitor

I've bought a bunch of film type capacitor as they were pretty cheap and I thought it was a good idea to get some and test them. (set here) So I'm trying to figure out what's the specific application ...
4
votes
1answer
332 views

Crystal, PCB Layout

I've completed a few circuit board layouts before, however this is my first time doing a layout with a oscillator/MCU. After doing some reading (via this site and datasheets) I've come up with the ...
1
vote
1answer
190 views

Smoothing and decoupling power source input

I am transforming an old battery-only radio so I can connect it through a DC input. I found an earlier model diagram that includes the DC input (picture attached). I have connected a 18 V DC source ...
4
votes
2answers
483 views

Does my circuit need decoupling caps? [duplicate]

I have a very simple design that I'm now working on the PCB layout for. And at the moment I'm thinking about the issue of decoupling capacitors. The board is very simple and only consists of this: ...
4
votes
1answer
247 views

Why would I need AC coupling if audio inputs already do the job?

I'm transmitting data from a microcontroller to a smarphone mic input and I was suggested to use this circuit to adapt the 5v digital signal: Taken from this tutorial The way I see it R2 and R3 ...
4
votes
3answers
271 views

Can two devices share a decoupling capacitor?

I am working on a circuit that has two devices that are each supposed to have decoupling capacitors. In this case however, the devices are right next to each other, and their power supply pins are ...
2
votes
3answers
302 views

Can multiple decoupling capacitors be replaced with a single low-inductance type?

It seems to be usual practice to put in decoupling capacitors of several different values, for example 0.1uF and 1uF (or sometimes 10uF, or 0.01uF depending on the device etc). I'm wondering if there ...
4
votes
2answers
126 views

Procedure for experimentally determining decoupling capability?

I'm looking for a bullet-point list of a technique to experimentally determine a design's decoupling capability. I have a design that I'm working on that seems to be susceptible to ESD events in the ...
3
votes
1answer
104 views

Changing decoupling capacitor values

I'm building a small board that uses the MMA8453Q Freescale Accelerometer. The datasheet requires a 4.7μF decouple capacitor on the \$V_{dd}\$ pin. I only have 3.3μF or 6.8μF capacitors on ...
-1
votes
1answer
95 views

through hole or SMD capacitor for high voltage powers [closed]

When TH and SMD caps are avalilable with same spec, which one to prefer for high voltage powers.?
4
votes
3answers
2k views

Calculating the value of bypass capacitors for an amplifier

I want to know if there is a rough any ready way of calculating the capacitance required to decouple the power supply used in an amplifier. (Rough and ready because I'll be adding 30% to the value ...
1
vote
1answer
77 views

Switch (dis)connects an LDO regulator from VBATT. Where should the filter cap go?

In my system, there are several DC-DC regulators all attached to a VBATT unregulated rail. One of the regulators is the LDO shown in the picture below. The user can connect it and disconnect it from ...
16
votes
4answers
3k views

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 ...
3
votes
4answers
636 views

Do I need filtering caps for a USB power supply?

I'm pulling 5V from USB for testing an IC. Should I put a capacitor in there to filter the power supply, or will it already be steady coming from the laptop? I don't have access to an oscilloscope, ...
4
votes
1answer
149 views

Substition of electrolytic capacitors in surface mount applications

I understand there are advantages and disadvantages against using electrolytic capacitors over others, such as ceramic, but from what I understand the main reason of choosing electrolytic caps is ...
3
votes
1answer
167 views

Is this a polarised capacitor

So I went to a local electronics retailer, Communica in Cape Town yesterday. I had a small shopping list including: 10x 10µF Ceramic Capacitor 10x 0.1µF Ceramic Capacitor The vendor didn't have ...
2
votes
2answers
226 views

parallel decoupling capacitors

In my circuit , I need decoupling capacitors , but my local shop doesn't have some values like 300nf so I need to put in parallel 3 of 100nf . the equivalent CAP would be 300nf but with multiple ...
4
votes
1answer
2k views

Reducing LED PWM Noise: Which is the best option?

Driving an LED with a microcontroller should be easy. But when looking into noise, things can get complex... As an instantaneous voltage indicator used in a variable power supply (which will be used ...
7
votes
1answer
527 views

Placement/routing of decoupling cap straddling oscillator guard ring on dsPIC

Changes in my design are forcing me to replace my 44-pin dsPIC33FFJ16MC304 with a 64-pin (same package size, finer pin pitch) dsPIC33FJ64MC506. In the datasheets for both chips, Microchip recommends a ...
5
votes
1answer
1k views

Sensor decoupling and noise reduction

I have an Arduino UNO board, and I wanted to design a simple 'sensor shield' --since all simple sensors has 3 pins (namely, SIG-5V-GND) and it is convenient to connect bunch of them directly-- and ...
0
votes
2answers
215 views

What formulas do I need to use to design a voltage regulator circuit for a zigbee radio?

I've written the code for my zigbee radios, but now I face the obstacle of getting them onto a carrier board to allow access to VCC, GND, TX, RX via a 4 wire connector. The supply voltage is 3.712 ...
3
votes
4answers
570 views

Decoupling capacitor across Raspberry Pi GPIO input (+ Arduino + robotics)

I've been messing around with a robot kit from Parallax (the BOE Shield Kit), which has a 5xAA (7.2 V?) power source. The BOE shield includes its own 5 V regulator, which is used to control ...
7
votes
1answer
499 views

Best place to place a decoupling capacitor

See this image which gives four options to place decoupling capacitors: (from http://www.learnemc.com/tutorials/Decoupling/decoupling01.html) I would say option (d) isn't good - I would recommend ...
33
votes
5answers
3k views

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 ...
1
vote
3answers
273 views

Which connection(s) to a decoupling capacitor should be shortest?

Circuit Cellar-Issue 210- has this question "Which connection(s) to a decoupling capacitor should be shortest?why?" in its "Test your EQ section". I couldn't understand what they meant 'Which ...
-2
votes
3answers
260 views

How many capacitors are required 3.3 V rail for 500 mA?

How much capacitance do I need on a 3.3 V rail with loading of ~500 mA? I have 22 µF capacitors that I can use. In general, what is a good rule of thumb on how much capacitance is ...
5
votes
2answers
325 views

How do I decople a microcontroller with odd number of ground pins?

I'm building a DIP adapter board for MSP430FR5739 and I want to include the decoupling capacitors on the adapter board itself. From what I can see, I'll need a capacitor on the analogue and digital ...
7
votes
1answer
493 views

Is my design good enough in terms of noise and EMI as its 80MHz MCU board [closed]

Recently I'm trying to design a PCB board for an MCU. The problem is I haven't considered any noise aspects before. As I'm in a contest for new electronics product run by our university I have to ...
2
votes
1answer
1k views

What's the use of the bypass capacitor on the LM380 amplifier?

I've read the LM380 amplifier data sheet and application notes, and they show a power supply ripple rejection number that's based on the size of the bypass capacitor. There are also a few designs that ...
24
votes
3answers
15k views

Can I replace all electrolytic capacitors with ceramic ones?

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 ...