Information about Ferrite Bead 100mA component

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Dear All,

I still feel strange on ferrite bead component. I do have some question about this component, hope can gain some knowledge from here.

1) May i know what's the actual unit reading for ferrite bead, is it on ampere, walt, ohm?
2) The circuit they request for Ferrite Bead 100mA. If my Vcc is +5V. Is it i have to choose 50Ohm ferrite bead?
3) What's the advantage for this ferrite bead component?
4) Can we put a small 30Ohm ferrite bead in series for every I/O signal, RS232 Tx/Rx signal, uC reset and IC Vcc?
5) If we apply this on RTC Vcc, can it improve the IC performance so that the time will run more accuracy? If yes, how to choose a rite Ferrite Bead?

Thank you.

 

[IanP]

Re: Ferrite Bead 100mA

(1) May i know what's the actual unit reading for ferrite bead, is it on ampere, walt, ohm?
It’s impedance in (ohms) at a given frequency .. sometimes the manufacturer add current rating ..

(2) The circuit they request for Ferrite Bead 100mA. If my Vcc is +5V. Is it i have to choose 50Ohm ferrite bead?
You choose any attenuation you think is suitable for your application, it doesn’t need to be 59ohms, it can be, for example 200ohms ..

(3) What's the advantage for this ferrite bead component?
http://www.sigcon.com/Pubs/edn/ferritebeads.htm
**broken link removed**

(4) Can we put a small 30Ohm ferrite bead in series for every I/O signal, RS232 Tx/Rx signal, uC reset and IC Vcc?
It is not a requirement to use ferrite beads on all lines, you can have them on power supply rails and not on signal inputs, or you can have different components on power rails and different on signal inputs .. I think you’ll have an idea when to use them once you go through the above links ..
(5) If we apply this on RTC Vcc, can it improve the IC performance so that the time will run more accuracy?
No ..

IanP
:|

 

[Help]

Re: Ferrite Bead 100mA

Dear IanP,

Thanks for your reply.

1)
I did found a few application sample normally they are using 100MHz for normal filtering.

2)
Let say the circuit input signal or IC supply need 50mA at Vcc=+5Volt. If we choose 500Ohm(5V/500Ohm=10mA), is it it will affected the current not enough sinking to signal/IC?


(3)
After read the information i still can't get much idea how/when to apply Ferrite Bead but i found a good article I would like to share with you. Please check the attach file.

(4)

It is not a requirement to use ferrite beads on all lines, you can have them on power supply rails and not on signal inputs,

If the power supply rails is +5V and let say my whole board current usage is 1A. So is it we have to choose <5Ohm ferrite bead? Can it overcome the Heating? (I don't think it will generate the heat, if using resistor it will generate the heat)

or you can have different components on power rails and different on signal inputs ..

May i know what do you meant? Can you draw a simple circuit as reference?

My i know how we differentiate the Digital Vcc and Analog Vcc? Normally, i'm using voltage regulator 5Volt+GND as my testing board main supply. Voltage regulator output supply is it we call it Analog Vcc?

(5) In the article they add a ferrite bead and Cap at ROM & RAM IC Vcc. if I using same concept to apply for flash memory. So, it will filter the Vcc noise and the flash memory data will not easy to corrupt. Am i rite?

Thanks

 

[FvM]

Re: Ferrite Bead 100mA

If we choose 500Ohm(5V/500Ohm=10mA)

The caculation is wrong, because ferrite bead Z is an AC impedance, it must not be confused with DC resistance. Typical ferrite bead DC resistances are < 1 ohm.

The rated DC current, e.g. 100 mA is mainly defined by the permissible overtemperature. To avoid impedance degradation due to magnetic saturation, the DC current must be consderably lower.

The most important application is keeping electromagnetic compatibility (EMC) regulations, regarding active (emission) as well as passive (susceptibility) behaviour.

 

[Help]

Re: Ferrite Bead 100mA

Dear FvM,

Thanks for your reply.

One thing i realize in the datasheet. If we choose the Lowest Impedance for the ferrite the DC Current rate will be highest and the DC Resistance is smaller. Is it lowest Impedance and lowest DC Resistance will improve the EMI filtering?

Is it possible to use a 10Ohm Impedance @ 100MHz, 500mA Rate Current, 0.1Ohm DCR at 5Volt Regulator output? Is it it is a ideal design?

Dear IanP,

I found a sample circuit which is Analog GND is separate with Digital GND just using a Ferrite. This sample circuit is similar to this http://www.sigcon.com/Pubs/edn/ferritebeads.htm Figure 1 diagram.

If in our design have a ADC (eg.ADC0834) IC in the PCB board then we should separate the ADC IC GND with the other TTL IC GND? If yes, what is the best ferrite bead value should consider?

Thank you,.

 

[karesz]

Ferrite Bead 100mA

Hi,
I dont think, that between your AGND-DGND more as 100mA will exist; I would take the BLM03AG241SN1...
Anyway, its DC resistance is relative big with ca. 1 OHM; you can find some others as i.e. the "0805" MPZ2012S221A from TDK, 220 Ohm at 100MHz, max. Rdc=0.05 Ohm & 2,5A capability_as 600 Ohm has max. Rdc 0.1 Ohm and 2A current capability...
Murata has other better types too...
Your ADC0834 seems to work with Clk edges of 125..200nsec, these means that your generated RF currents/disturbances are mostly in the band of 10...50/70MHz, I would take a 100-300 Ohm impedance version, as even TDK family above has it.
Otherwise; Its "only" an 8-Bit converter, the spike problems are so not tragical IF YOUR LAYOUT IS PROPERLY ROUTED & DGND/AGND parts ARE SEPARATED with ISOLATION SLOTS, but CONNECTED (shorted) AT both GND PINS OF THE ADC ...
K.

 

[FvM]

Ferrite Bead 100mA

In my opinion, it's very unusual to separate ground nodes by ferrite beads. The posted link doesn't suggest it.

Generally, DC resistance of ferrite beads is not directly linked to AC impedance.

 

[karesz]

Ferrite Bead 100mA

Hallo Frank,
some newer High-speed ADC appl notes are said/proposed it_Im not sure, was it ADI or TI?...
K.

 

[Help]

Re: Ferrite Bead 100mA

Dear All,

I have do alot of study on net. I found a nice information about the ferrite bead. Hope can this information can help each other.

Important performance specifications to consider when searching for ferrite beads include impedance range, impedance tolerance, impedance testing frequency, DCR, rated DC current, and operating temperature. The impedance is the total resistance to the flow of current, including AC and DC components. The DC component is simply the DC resistance of the device. The AC component includes the bead reactance. The impedance tolerance is the allowed amount of variation from the nominal value as specified by the manufacturer. The impedance testing frequency is the frequency at which the bead impedance is tested. Direct current resistance (DCR) is the resistance of the inductor winding measured using DC current. The DCR is most often minimized in the design of an inductor and specified as a maximum rating. The rated DC current (IDC) is the level of continuous direct current that can be passed through the inductor with no damage. The DC current level is based on a maximum temperature rise at the maximum rated ambient temperature. The rated current is related to the inductor's ability to minimize the power losses in the winding by having a low DC resistance. For low frequency currents the RMS current can be substituted for the DC rated current. The operating temperature for ferrite beads is the full required range of ambient operating temperature.

Direct current resistance (DCR) is the resistance of the inductor winding measured using DC current. The DCR is most often minimized in the design of an inductor and specified as a maximum rating.

May i know what does it mean?

Thank you.

 

[IanP]

Re: Ferrite Bead 100mA

Quote:
Direct current resistance (DCR) is the resistance of the inductor winding measured using DC current. The DCR is most often minimized in the design of an inductor and specified as a maximum rating.

May i know what does it mean?

DC resistance is just the resistance of the wire used to wind an inductor ..
When you apply dc power source and you measure dc voltage and dc current the R[dc] = U/I – simple Ohm’s law ..
In order to minimize this resistance a thicker wire is used: thicker wire –> bigger cross-section –> lower resistance ..
Or, they use shorter wire and a bead with higher magnetic properties to achieve similar inductance .. and so on ..

See: R2 in "equivalet circuit" - https://www.tdk.co.jp/etvcl/equivalent/bead.htm

IanP
:|

 

[FvM]

Re: Ferrite Bead 100mA

some newer High-speed ADC appl notes are said/proposed it

May be. I doubt, that the concept holds good for other circuits than a development kit with one ADC and one digital device. But I agree, that there are special cases where separated ground nodes/planes with ferrite bead isolation can be reasonable. Sometimes I used it, too.

The discussion was however about ferrite bead basics. I don't see an understandable motivation to apply the said concept in the discussed circuit. In other words, it's rather confusing the purpose of a ferrite bead than giving an instructive example.

May i know what does it mean?

The maximum rating point says, they specify a maximum DCR instead of a designed/typical value. Some manufaturers (e.g. my preferred Wuerth electronics) actually specifies both.