Hi all,
I'm developing a product and writing codes using a OLIMEX board and now
its time to design the schematics of the "real" product. The board has some
"ferrite bead" but I cant find any extra information about it. Looking at other
boards schematics the ferrite bead is there too, but again, no specification.
KEIL has ferrites named "BLM".
Does anyone can tell more about these ferrite beads ? I mean the specifications,
inductance and etc.
Thanks in advance.
Wagner Loebel
Ferrite bead
Started by ●February 22, 2010
Reply by ●February 22, 20102010-02-22
Hi,
> I'm developing a product and writing codes using a OLIMEX board and
> now its time to design the schematics of the "real" product. The board
> has some "ferrite bead" but I cant find any extra information about it.
> Looking at other boards schematics the ferrite bead is there too, but
> again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
BLM is a Murata part number.
Look on digikey: ferrite BLM
Cheers,
Dave
> I'm developing a product and writing codes using a OLIMEX board and
> now its time to design the schematics of the "real" product. The board
> has some "ferrite bead" but I cant find any extra information about it.
> Looking at other boards schematics the ferrite bead is there too, but
> again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
BLM is a Murata part number.
Look on digikey: ferrite BLM
Cheers,
Dave
Reply by ●February 22, 20102010-02-22
Hi Dave. Thanks for reply.
I search on DIGIKEY and MOUSER and WOW.... a lot of options:
BLM18EG601SN1D -->> 600ohms
BLM18RK221SN1D -->> 220ohms
BLM21AF121SH1D -->> 120ohms
BLM18HD471SH1D -->> 470ohms
and etc, etc....
Now I have the specs, but.... which one I place in my schematics ? I guess I need to do some calc, right ?
Thanks in advance.
Wagner
----- Original Message -----
From: David Hawkins
To: l...
Sent: Monday, February 22, 2010 6:16 PM
Subject: Re: [lpc2000] Ferrite bead
Hi,
> I'm developing a product and writing codes using a OLIMEX board and
> now its time to design the schematics of the "real" product. The board
> has some "ferrite bead" but I cant find any extra information about it.
> Looking at other boards schematics the ferrite bead is there too, but
> again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
BLM is a Murata part number.
Look on digikey: ferrite BLM
Cheers,
Dave
I search on DIGIKEY and MOUSER and WOW.... a lot of options:
BLM18EG601SN1D -->> 600ohms
BLM18RK221SN1D -->> 220ohms
BLM21AF121SH1D -->> 120ohms
BLM18HD471SH1D -->> 470ohms
and etc, etc....
Now I have the specs, but.... which one I place in my schematics ? I guess I need to do some calc, right ?
Thanks in advance.
Wagner
----- Original Message -----
From: David Hawkins
To: l...
Sent: Monday, February 22, 2010 6:16 PM
Subject: Re: [lpc2000] Ferrite bead
Hi,
> I'm developing a product and writing codes using a OLIMEX board and
> now its time to design the schematics of the "real" product. The board
> has some "ferrite bead" but I cant find any extra information about it.
> Looking at other boards schematics the ferrite bead is there too, but
> again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
BLM is a Murata part number.
Look on digikey: ferrite BLM
Cheers,
Dave
Reply by ●February 22, 20102010-02-22
Hi Wagner,
> Hi Dave. Thanks for reply.
>
> I search on DIGIKEY and MOUSER and WOW.... a lot of options:
>
> BLM18EG601SN1D -->> 600ohms
> BLM18RK221SN1D -->> 220ohms
> BLM21AF121SH1D -->> 120ohms
> BLM18HD471SH1D -->> 470ohms
> and etc, etc....
>
> Now I have the specs, but.... which one I place in my schematics ? I
> guess I need to do some calc, right ?
The calculations are pretty much:
a) Current-rating of the bead.
b) Impedance at the device at your operating frequency.
Then on the circuit you place a PI filter consisting of
100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
This arrangement filters power-into the circuit, and filters
noise being generated back onto the power rail (where it could
be picked up by other circuits).
Think of the ferrite as being a nicer kind of resistor.
It does not have (much) resistance at DC, so there is no IR
drop as your circuit draws current, but at high frequency
it acts as an RC filter, where the R is the ferrite bead
impedance at the frequency you care about. Likely your
uC clock is a few MHz, so you'll want a bead with high
impedance over the range of harmonics of that clock.
The calculation doesn't have to be that accurate. So
long as you have the right footprint and current rating,
you can always change things if you measure an EMI
problem.
Cheers,
Dave
> Hi Dave. Thanks for reply.
>
> I search on DIGIKEY and MOUSER and WOW.... a lot of options:
>
> BLM18EG601SN1D -->> 600ohms
> BLM18RK221SN1D -->> 220ohms
> BLM21AF121SH1D -->> 120ohms
> BLM18HD471SH1D -->> 470ohms
> and etc, etc....
>
> Now I have the specs, but.... which one I place in my schematics ? I
> guess I need to do some calc, right ?
The calculations are pretty much:
a) Current-rating of the bead.
b) Impedance at the device at your operating frequency.
Then on the circuit you place a PI filter consisting of
100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
This arrangement filters power-into the circuit, and filters
noise being generated back onto the power rail (where it could
be picked up by other circuits).
Think of the ferrite as being a nicer kind of resistor.
It does not have (much) resistance at DC, so there is no IR
drop as your circuit draws current, but at high frequency
it acts as an RC filter, where the R is the ferrite bead
impedance at the frequency you care about. Likely your
uC clock is a few MHz, so you'll want a bead with high
impedance over the range of harmonics of that clock.
The calculation doesn't have to be that accurate. So
long as you have the right footprint and current rating,
you can always change things if you measure an EMI
problem.
Cheers,
Dave
Reply by ●February 22, 20102010-02-22
Dave, thanks for this valuable info. Now I'll get my HP and do my homework.
:)
Thank you very much.
Regards,
Wagner
----- Original Message -----
From: David Hawkins
To: l...
Sent: Monday, February 22, 2010 6:45 PM
Subject: Re: [lpc2000] Ferrite bead
Hi Wagner,
> Hi Dave. Thanks for reply.
>
> I search on DIGIKEY and MOUSER and WOW.... a lot of options:
>
> BLM18EG601SN1D -->> 600ohms
> BLM18RK221SN1D -->> 220ohms
> BLM21AF121SH1D -->> 120ohms
> BLM18HD471SH1D -->> 470ohms
> and etc, etc....
>
> Now I have the specs, but.... which one I place in my schematics ? I
> guess I need to do some calc, right ?
The calculations are pretty much:
a) Current-rating of the bead.
b) Impedance at the device at your operating frequency.
Then on the circuit you place a PI filter consisting of
100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
This arrangement filters power-into the circuit, and filters
noise being generated back onto the power rail (where it could
be picked up by other circuits).
Think of the ferrite as being a nicer kind of resistor.
It does not have (much) resistance at DC, so there is no IR
drop as your circuit draws current, but at high frequency
it acts as an RC filter, where the R is the ferrite bead
impedance at the frequency you care about. Likely your
uC clock is a few MHz, so you'll want a bead with high
impedance over the range of harmonics of that clock.
The calculation doesn't have to be that accurate. So
long as you have the right footprint and current rating,
you can always change things if you measure an EMI
problem.
Cheers,
Dave
Thank you very much.
Regards,
Wagner
----- Original Message -----
From: David Hawkins
To: l...
Sent: Monday, February 22, 2010 6:45 PM
Subject: Re: [lpc2000] Ferrite bead
Hi Wagner,
> Hi Dave. Thanks for reply.
>
> I search on DIGIKEY and MOUSER and WOW.... a lot of options:
>
> BLM18EG601SN1D -->> 600ohms
> BLM18RK221SN1D -->> 220ohms
> BLM21AF121SH1D -->> 120ohms
> BLM18HD471SH1D -->> 470ohms
> and etc, etc....
>
> Now I have the specs, but.... which one I place in my schematics ? I
> guess I need to do some calc, right ?
The calculations are pretty much:
a) Current-rating of the bead.
b) Impedance at the device at your operating frequency.
Then on the circuit you place a PI filter consisting of
100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
This arrangement filters power-into the circuit, and filters
noise being generated back onto the power rail (where it could
be picked up by other circuits).
Think of the ferrite as being a nicer kind of resistor.
It does not have (much) resistance at DC, so there is no IR
drop as your circuit draws current, but at high frequency
it acts as an RC filter, where the R is the ferrite bead
impedance at the frequency you care about. Likely your
uC clock is a few MHz, so you'll want a bead with high
impedance over the range of harmonics of that clock.
The calculation doesn't have to be that accurate. So
long as you have the right footprint and current rating,
you can always change things if you measure an EMI
problem.
Cheers,
Dave
Reply by ●February 22, 20102010-02-22
If I am not wrong, olimex also use ferrites bread to the cc/cc converter for
the backlight voltage..
2010/2/22 Wagner Loebel
> Dave, thanks for this valuable info. Now I'll get my HP and do my
> homework. :)
>
> Thank you very much.
>
> Regards,
>
> Wagner
>
> ----- Original Message -----
> *From:* David Hawkins
> *To:* l...
> *Sent:* Monday, February 22, 2010 6:45 PM
> *Subject:* Re: [lpc2000] Ferrite bead
>
> Hi Wagner,
>
> > Hi Dave. Thanks for reply.
> >
> > I search on DIGIKEY and MOUSER and WOW.... a lot of options:
> >
> > BLM18EG601SN1D -->> 600ohms
> > BLM18RK221SN1D -->> 220ohms
> > BLM21AF121SH1D -->> 120ohms
> > BLM18HD471SH1D -->> 470ohms
> > and etc, etc....
> >
> > Now I have the specs, but.... which one I place in my schematics ? I
> > guess I need to do some calc, right ?
>
> The calculations are pretty much:
>
> a) Current-rating of the bead.
>
> b) Impedance at the device at your operating frequency.
>
> Then on the circuit you place a PI filter consisting of
> 100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
>
> This arrangement filters power-into the circuit, and filters
> noise being generated back onto the power rail (where it could
> be picked up by other circuits).
>
> Think of the ferrite as being a nicer kind of resistor.
> It does not have (much) resistance at DC, so there is no IR
> drop as your circuit draws current, but at high frequency
> it acts as an RC filter, where the R is the ferrite bead
> impedance at the frequency you care about. Likely your
> uC clock is a few MHz, so you'll want a bead with high
> impedance over the range of harmonics of that clock.
>
> The calculation doesn't have to be that accurate. So
> long as you have the right footprint and current rating,
> you can always change things if you measure an EMI
> problem.
>
> Cheers,
> Dave
>
>
>
the backlight voltage..
2010/2/22 Wagner Loebel
> Dave, thanks for this valuable info. Now I'll get my HP and do my
> homework. :)
>
> Thank you very much.
>
> Regards,
>
> Wagner
>
> ----- Original Message -----
> *From:* David Hawkins
> *To:* l...
> *Sent:* Monday, February 22, 2010 6:45 PM
> *Subject:* Re: [lpc2000] Ferrite bead
>
> Hi Wagner,
>
> > Hi Dave. Thanks for reply.
> >
> > I search on DIGIKEY and MOUSER and WOW.... a lot of options:
> >
> > BLM18EG601SN1D -->> 600ohms
> > BLM18RK221SN1D -->> 220ohms
> > BLM21AF121SH1D -->> 120ohms
> > BLM18HD471SH1D -->> 470ohms
> > and etc, etc....
> >
> > Now I have the specs, but.... which one I place in my schematics ? I
> > guess I need to do some calc, right ?
>
> The calculations are pretty much:
>
> a) Current-rating of the bead.
>
> b) Impedance at the device at your operating frequency.
>
> Then on the circuit you place a PI filter consisting of
> 100pF/1nF -> ferrite -> 100pf/1nF -> device being powered
>
> This arrangement filters power-into the circuit, and filters
> noise being generated back onto the power rail (where it could
> be picked up by other circuits).
>
> Think of the ferrite as being a nicer kind of resistor.
> It does not have (much) resistance at DC, so there is no IR
> drop as your circuit draws current, but at high frequency
> it acts as an RC filter, where the R is the ferrite bead
> impedance at the frequency you care about. Likely your
> uC clock is a few MHz, so you'll want a bead with high
> impedance over the range of harmonics of that clock.
>
> The calculation doesn't have to be that accurate. So
> long as you have the right footprint and current rating,
> you can always change things if you measure an EMI
> problem.
>
> Cheers,
> Dave
>
>
>
Reply by ●February 23, 20102010-02-23
Wurth has more common ferrite bead components with short lead times then
Murata; in Cortex-M3 designs I use them to filter analog and reference
pins of the adc; I use 742792691 (Wurth part code). My filter is a 1uF
ceramic capacitor between 3.3V and GND, 1 ferrite between 3.3V and VDDA,
a 100nF capacitor betwwen VDDA and GND, 1 ferrite bead between GND and
VSSA, 1 ceramic 100nF capacitor between VSSA and GND.
Same thing for VREF+ / VREF- and 3.3V / GND.
I simulated it with LTSpiceIV and it works remarkable well.
Wagner Loebel ha scritto:
>
>
> Hi all,
>
> I'm developing a product and writing codes using a OLIMEX board
> and now its time to design the schematics of the "real" product. The
> board has some "ferrite bead" but I cant find any extra information
> about it. Looking at other boards schematics the ferrite bead is there
> too, but again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
>
>
> Thanks in advance.
>
>
> Wagner Loebel
>
>
Murata; in Cortex-M3 designs I use them to filter analog and reference
pins of the adc; I use 742792691 (Wurth part code). My filter is a 1uF
ceramic capacitor between 3.3V and GND, 1 ferrite between 3.3V and VDDA,
a 100nF capacitor betwwen VDDA and GND, 1 ferrite bead between GND and
VSSA, 1 ceramic 100nF capacitor between VSSA and GND.
Same thing for VREF+ / VREF- and 3.3V / GND.
I simulated it with LTSpiceIV and it works remarkable well.
Wagner Loebel ha scritto:
>
>
> Hi all,
>
> I'm developing a product and writing codes using a OLIMEX board
> and now its time to design the schematics of the "real" product. The
> board has some "ferrite bead" but I cant find any extra information
> about it. Looking at other boards schematics the ferrite bead is there
> too, but again, no specification. KEIL has ferrites named "BLM".
>
> Does anyone can tell more about these ferrite beads ? I mean the
> specifications, inductance and etc.
>
>
> Thanks in advance.
>
>
> Wagner Loebel
>
>
Reply by ●February 23, 20102010-02-23
Hi M.Manca.
Nice. Thank you the reply.
Regards,
Wagner
----- Original Message -----
From: M. Manca
To: l...
Sent: Tuesday, February 23, 2010 5:07 AM
Subject: Re: [lpc2000] Ferrite bead
Wurth has more common ferrite bead components with short lead times then Murata; in Cortex-M3 designs I use them to filter analog and reference pins of the adc; I use 742792691 (Wurth part code). My filter is a 1uF ceramic capacitor between 3.3V and GND, 1 ferrite between 3.3V and VDDA, a 100nF capacitor betwwen VDDA and GND, 1 ferrite bead between GND and VSSA, 1 ceramic 100nF capacitor between VSSA and GND.
Same thing for VREF+ / VREF- and 3.3V / GND.
I simulated it with LTSpiceIV and it works remarkable well.
Wagner Loebel ha scritto:
Hi all,
I'm developing a product and writing codes using a OLIMEX board and now its time to design the schematics of the "real" product. The board has some "ferrite bead" but I cant find any extra information about it. Looking at other boards schematics the ferrite bead is there too, but again, no specification. KEIL has ferrites named "BLM".
Does anyone can tell more about these ferrite beads ? I mean the specifications, inductance and etc.
Thanks in advance.
Wagner Loebel
Nice. Thank you the reply.
Regards,
Wagner
----- Original Message -----
From: M. Manca
To: l...
Sent: Tuesday, February 23, 2010 5:07 AM
Subject: Re: [lpc2000] Ferrite bead
Wurth has more common ferrite bead components with short lead times then Murata; in Cortex-M3 designs I use them to filter analog and reference pins of the adc; I use 742792691 (Wurth part code). My filter is a 1uF ceramic capacitor between 3.3V and GND, 1 ferrite between 3.3V and VDDA, a 100nF capacitor betwwen VDDA and GND, 1 ferrite bead between GND and VSSA, 1 ceramic 100nF capacitor between VSSA and GND.
Same thing for VREF+ / VREF- and 3.3V / GND.
I simulated it with LTSpiceIV and it works remarkable well.
Wagner Loebel ha scritto:
Hi all,
I'm developing a product and writing codes using a OLIMEX board and now its time to design the schematics of the "real" product. The board has some "ferrite bead" but I cant find any extra information about it. Looking at other boards schematics the ferrite bead is there too, but again, no specification. KEIL has ferrites named "BLM".
Does anyone can tell more about these ferrite beads ? I mean the specifications, inductance and etc.
Thanks in advance.
Wagner Loebel
