Ferrites in PCB Design: What the Experts Say

Рет қаралды 7,296

Күн бұрын

*Ferrites in PCB Design: What the Experts Say*
Are you curious about the role of ferrite beads in PCB design? Join Tech Consultant Zach PEterson on a tour of industry experts sharing their perspectives on using ferrite beads in PCB design.
🔍 *In This Video:*
- *Zach Peterson* from Altium Academy dives into a controversial statement about ferrites made during a USB isolator design review.
- *Expert Opinions**: Hear from renowned industry experts like **Steve Sandler**, **Ben Dannan**, and **Heidi Barnes* on the appropriate use of FERRITES IN PCB DESIGN.
- **Practical Examples**: Understand the implications of using a FERRITE BEAD on power rails and the potential issues they can cause.
- **Community Insights**: Read and discuss comments from LinkedIn and other platforms where professionals debate the usage of ferrite beads.
🔗 Links!
Design Review that Started All of This: • The Best Time to Use a...
Picotest’s Water Cooled Probe with Steve Sandler: • Picotest’s Water Coole...
Quality Reports, Vendor Models, & EDI CON with Ben Dannan: • Quality Reports, Vendo...
Ferrites in Power Delivery Networks - Part One: • Ferrites in Power Deli...
Ferrites in Power Delivery Networks - Part Two: • Ferrites in Power Deli...
Power Integrity and Simulations with Heidi Barnes: • Power Integrity and Si...
Omicron Webinar: Output Impedance of Power Supplies: • Webinar: Output Impeda...
👉 Exclusive 15 Days Free Altium Designer Access: www.altium.com/promotions/alt...
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#PCBDesign #FerriteBeads #PowerIntegrity #ElectronicDesign #AltiumAcademy
0:00 Intro
0:33 The Best Time to Use a Ferrite is Never
7:05 Ferrites on Output of Power Supply?
9:12 Higher Frequencies & Resonances
11:53 3 Key Takeaways

Пікірлер: 40

@GaborGubicza 27 күн бұрын

"don't forget to call your fabricator" ... Best Closing line EVER XD ... Funny, because it's true. Take care.

@alexanderquilty5705 26 күн бұрын

You have me convinced Zach! Wish I had more experience using these SPICE models. I'll get there eventually!

@myetis1990 26 күн бұрын

Hey Zach, thank you for the great video, ok the time for ferrites is never, but Rail filtering has always seemed complicated, Actually it would be nice if there was a roadmap video. For example, how do we know we need a filter? Which filter is more suitable for which job? If we want to simulate these, how do we do it? Can we be sure with certain calculations without simulating? How do we know if we really need ferrite beads? An example pi filter design would be very useful. Whenever I look at a design, filter values taken from the design guide are used, but won't this filter become ineffective when a different dcdc converter is used?

@Zachariah-Peterson 10 күн бұрын

I did another one after this where I compared the basic filter options. I think the moral of the story is that a damped pi filter looks very similar to a ferrite filter at low frequencies and near cutoff, so they can be vey helpful for attenuating a specific frequency range while allowing DC power delivery.

@idk2412 27 күн бұрын

Great video! I always enjoy a montage of experts coming to destroy ferrites :) A couple of questions: 1) You mentioned in your summary point #2 isolating rails with a ferrite, "you will need to qualify it in test and measurement". Outside of getting on a scope and looking for resonances, what else would you suggest? 2) Your summary point #3 mentions noise being created by the ferrite which will make it's way to your digital I/O's. Are you saying from the H or E field being generated that will couple to IO's? What is the source of the noise? Or, is that comment the same as Joanna McLellan, where she says the pin will ring because no current and be sourced since it's high-impedance? Cheers

@Zachariah-Peterson 10 күн бұрын

1) it's a simple matter of monitoring the isolated rail with and without the main rail running, then compare the two situations. If the isolated rail is an I/O supply, you can probably more easily monitor the I/Os, and then short across the ferrite as needed to "remove" it from the PDN. 2) That comment is basically the same as Joanna's, the origin of the noise is an underdamped resonance in the rail voltage when the I/O switches. As I/Os switch, they are attempting to draw current from the power supply and capacitor bank (essentially an RLC circuit), but those elements can only respond so quickly. As is known from RLC circuit theory, any additional inductance will slow down the response to an input current pulse and thus the transient response in this 2nd order circuit has a high chance of being underdamped. You could add damping to make the system critically damped, but that now reduces power efficiency and it will cause the bandwidth of the control loop and the PDN's power delivery range to be attenuated to lower frequencies, so the PDN will be unable to deliver power for fast edge rate signals.

@techydude 27 күн бұрын

Perhaps chip maker datasheets need to be submitted to ‘peer review’ before being published? 🤣

@petersage5157 26 күн бұрын

I must confess to taking some datasheet example circuits as Gospel. A little design review outside the developers' walled gardens would be good for everyone, including the developers.

@techydude 26 күн бұрын

@@petersage5157 The trap we easily fall into is treating every datasheet as though it were handed down from the heavens like Moses and the 10 Commandments, a fully formed document of perfection which has been sweated over by a squadron of pixies from the black forrest. Sure, datasheets are a primary source of truth about a component, but that primacy still exists on a spectrum of accuracy, quality, completeness, even the manufacturer's own degree of giving-a-fuck-ness. They're often compiled by many engineers, and maintained by a different subset of engineers spanning sometimes decades, from the oldest and most experienced, to interns. And that's all before getting to the 'implementation guidance' parts of data sheets, where even more breadth of experience in the many applications and industries in which this component might be used comes into play! Also, when it comes to EMC, copy-paste perpetuates old/bad techniques year after year after year.

@alexanderquilty5705 26 күн бұрын

Lee Ritchey even says that it is still true today that most people creating the data sheets don't understand board layout. Unfortunately we are stuck with it until those respective components become EoL. Which could be a loooong time 😅

@Zachariah-Peterson 10 күн бұрын

Oh man that would be interesting for sure, their eval/reference designs should also be peer reviewed. There are some companies I have found that actually understand some things about board layout, for example Texas Instruments has an internal CAD team that does a great job. Other companies though.... not so much.

@flisboac 27 күн бұрын

What about using ferrite beads to isolate the same (positive, not gound) power rail for use in both digital and analog power domains in an IC? An example: some microcontrollers have separate digital and analog power supply realms, mostly used for ADC and whatnot, and in most cases you won't have two different power supplies to use exclusively for analog stuff (for whatever reason, e.g. size/budget constraints, etc.). What I commonly see people recommending is to put a ferrite bead in series with a, say, 5V supply, followed by a capacitor (generally a bulk and a decoupling, if my terminology here is right) to ground. All of this considering proper ground planes in the PCB (not isolated, per se, just properly separated). Is that an acceptable use case, or is it representative of the same pitfalls you guys discussed in this video (useless, or worrisome)? (Sorry for the admittedly beginner's question; thinking about this use case specifically, I couldn't quite transfer and infer anything from the video.)

@Zachariah-Peterson 10 күн бұрын

This is one of the common instances where I see ferrites used and it really depends strongly on what you are trying to measure with the analog rail. This is equivalent to the case of isolating a dedicated rail for a PLL, and I have seen mixed results. If the analog rail is only measuring at DC, and the circuitry in the analog interface will not need to draw fast pulses of current, then there is no risk that the voltage transients on the isolated analog rail will be seen on the main digital rail. Whether this will actually work depends on the ADC type (sigma-delta, SAR, etc.), whether you are isolating just an external reference of if it's the whole interface.

@hgo31079 27 күн бұрын

Thanks for the insights Zach.

@myetis1990 26 күн бұрын

Finally I was convinced and decided threw away all the ferrite beads I was holding in case I needed them one day :) Or no, I will give it as a gift to someone I don't like, telling them it is a 100nf cap :)

@Shrek_Holmes 26 күн бұрын

I only ever use ferrites on the AC power input or dc from an external source that is unclean or unregulated.

@Growler-F18 27 күн бұрын

Thank you , I learned something of great value!😮😊

@AlbertRei3424 25 күн бұрын

What an amazing concept of video! Doing a similar thing for other controversial matter would be great too! (exemple: Ground Pour, best 4 layer stack up, shielding connection...)

@cedricb2344 23 күн бұрын

Shielding in particular would be very interesting

@Zachariah-Peterson 10 күн бұрын

Thanks, we have done some of this on 4 layer stackups, such as on the usage of SIG-GND-PWR-SIG stackups. Take a look around at the videos on the channel.

@thomassorensen7907 Сағат бұрын

Hi I know the ferrite is making it difficult to supply high frequency content on the output of a power supply, but would the decoupling caps on the high frequency IC not take care of this?

@leeslevin7602 26 күн бұрын

Brilliant! Thank you. 👏

@robertdixon8238 26 күн бұрын

Hi Zach, Great video, about a subject that is misunderstood by so many. Is there a case for ferrite beads on signal lines, particularly I/O onto and off PCB to a cable, etc? I'll be recommending this video for our team, as some still believe that appnotes and datasheets are correct, and can be blindly followed ... !!!! And of course, "What problem are you trying to solve?" Needs to be asked for every part on the schematic! Thanks.

@Zachariah-Peterson 10 күн бұрын

Thanks for watching. About the I/O lines, there are magnetics used on HDMI for example, but these components are built specifically to ensure compliance with the HDMI standard. Just because they do it in that instance does not mean you should do it in all other instances. I think that omitting that thought process is how we got to the current state of things, where ferrites are just applied everywhere without good judgement.

@fedimakni1200 27 күн бұрын

Thank you for all the amazing videos Related to this topic: We have a product that requires the use of a long cables from the DC Power supply (12/24V) to the PCB (which power uC and inductive and resistive loads) that long cable (around 5m) of course will cause some noise, voltage spikes when we PWM it... what do you think the best way to filter that voltage source in order to supply clean voltage to loads and ICs? Do you think Pi filter with inductor and capacitor is better instead of ferrite or just using higher decoupling or there are other options? Thanks.

@Duracellmumus 26 күн бұрын

The main problem is the AC content on long cable and its high inductance. Then the second one is a high resistance and a not constant DC load. So this is can be more complex to slove with only CLC filters. The possible way is put only a near-constant (dc) load to the cable and u have to deal only with the cable resistance/voltage droping. The second way is reduceing the current fructuating frequency to minimum and desing a remote-sense-ing psu what is stabile with long feedback and conservative load fluctuation. In that case may have to shild the cable from RF noise. The third way is isolate the high current load from the sensitive parts at the psu output. The load is olso have to switch with galvanic isolated driver.

@ats89117 27 күн бұрын

Jim Williams wrote many articles and made many videos on when it was appropriate and not appropriate to use ferrites in a design. Unfortunately, the level of ignorance has increased since he passed away...

@naorp2025 25 күн бұрын

Hi zach great video, Some suppliers suggest using ferrite for isolation on the power supply and isolation between digital and analog ground. Do you think it is necessry? Also,what kind of filter should i use on the power supply if i need low ripple, something like an lc filter will be enoght?

@Zachariah-Peterson 10 күн бұрын

Thanks for watching. What you've described is one of the worst uses for a ferrite bead, the only thing it does is it isolates your board from successful EMC testing. In most cases, just use a single ground for all digital and analog. Your EMC test results will thank you later.

@Duracellmumus 26 күн бұрын

I hate the ferrite without low impedance current path to the ground from load. Some time i put a realy small 33-100pf mlcc’s across the dgnd and dpower pins to keep the HF impedance under controll and prevent this HF current to flow thru and spreading on the ground. The next one 100nf is too far and too slow to deal with. In most of case this trick can make the ferrite works OK so get better noise performance with then without. The most of the desing flaws are done with inductors, when is placed paralel with other inductors like traces, resistors or shilded cables. Or placed to close to metal objects like shields or screws. I am not a circuit designer, but many times i have to solve miss beheves and or noise problems in current designs.

@mx.olydian2111 22 күн бұрын

Is it reasonable/practical to constrain my circuit designs to ones where I'm not introducing information faster than the quarter wavelength rule suggests? I think for all of my purposes i don't actually need rise times and frequencies that high for 90% of applications My question is does this constrain my hardware choices too much? It looks to me that most of the hardware out there is just too zoomy and I'm not sure how to proceed as a person who would like to design analog and (particularly) digital circuits that operate in the realm of topology instead of geometry How much can i do here? I feel as though the speed of light is plenty fast but most of the PCB design information i can find seems to contradict that perception, it feels like I need a HAM license to make PCBs sometimes

@petersage5157 26 күн бұрын

tl;dw: "If you want an inductor, put an inductor." Joking aside, and speaking of inductors, I know of power amp designs that recommend axial series output resistors with a parallel inductor of N gauge enameled wire wound X times around the resistor body. Whiskey Tango actual Foxtrot?! It's a low value resistance and you presumably want a known (or at least predictable) inductance; specify a wire wound resistor.

@sXAPOLLls 27 күн бұрын

I think the only use of ferrite beads is on analog power rail, but after you need to put big capacitor with resistor to groung and smaller close to pin to ground. This should eliminate resonance problem

@Zachariah-Peterson 10 күн бұрын

It depends on what is the frequency at which the analog system will be operating. Is it DC, moderate frequency, or a range of frequencies? Also, what is the circuit doing? Is this an ADC and your isolated power rail is powering the entire system, or is your isolated rail just a voltage reference? There are many questions to answer here so it is quite hard to generalize.