Timeline for Correct Placement of Series Ferrite Beads to Avoid DC Disconnect During Power Cycling
Current License: CC BY-SA 4.0
29 events
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| May 27 at 15:24 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 20 at 11:47 | vote | accept | Firas Abd El Gani | ||
| May 19 at 12:04 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 19 at 11:52 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 17 at 12:19 | history | became hot network question | |||
| May 17 at 4:33 | answer | added | Tim Williams | timeline score: 7 | |
| May 17 at 3:22 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 17 at 2:33 | answer | added | Kuba hasn't forgotten Monica | timeline score: 5 | |
| May 17 at 1:31 | comment | added | Tim Williams | What type are the capacitors, particularly on VIN_ALW? The previous version had a TVS, what was the rationale to discard this? | |
| May 17 at 1:26 | comment | added | Tim Williams | If you use five (or more) ferrite beads in parallel, are you getting enough impedance value from them? The part is already 30 ohms. Perhaps you would find an inductor more practical at this point? (Maintains its impedance at up to rated Isat current; has lower losses.) | |
| May 17 at 1:25 | history | edited | Tim Williams | CC BY-SA 4.0 |
Added figures and text from comment; please edit your question when adding relevant information so it is immediately visible to readers.
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| May 16 at 18:42 | comment | added | RogerDodger | Unless you really know what you are doing, you will often cause more problems than solving them when using ferrites. General advice when reading today's articles or watching webinars is not to use them, especially in this scenario, positive input into some IC or MCU. Just make sure the supply is clean, good filtering, local bypass/bulks, proper stackup and layout, and you should be good without the use of ferrites for this app | |
| May 16 at 18:21 | answer | added | John Birckhead | timeline score: 4 | |
| May 16 at 16:35 | comment | added | Firas Abd El Gani | There are always a load. VIN_ALW goes on 5V DC-DC and an LDO on the Carrier board: drive.google.com/file/d/16dEqSYE9n0Skunqlpiuiif4C-ed9WpTT/… VIN_ALW: goes to B2B to which we connect a SoM that has the CPU which is powered from voltages that are generated from the VIN_ALW rail: drive.google.com/file/d/16dideC_KXOgP7bTwuXe_gyk61d4iyir3/… One thing I can tell for sure that when this issue happens, when I unplug the power connector (which is connected to LAB PSU), it takes around 12 seconds to discharge the capacitors. | |
| May 16 at 16:19 | comment | added | smajli | Item to check: you mentioned that you have PSU connected, 0W consumption, caps charged. How is it possible, caps not discharging? No load? Isn't a problem lay further, somewhere on the other side of +VIN_ALW. What are you powering? Does it has solid connection? | |
| May 16 at 16:15 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 16 at 15:45 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 16 at 15:36 | comment | added | Firas Abd El Gani | Phoenix 1827868 didn't show this problem in other products. while the power consumption is similar. I might have exaggerated with the 8A-9A range. it's usually less than that. the system consumes 90W at maximum, with 20V as input voltage, but it might have certain spikes at power-up which can jump over 5A. the PSU is capable of handling such spikes for short amount of time. | |
| May 16 at 15:26 | comment | added | smajli | Another point: Phoenix 1827868 may be guilty. It has 8A max current. Have you tried to omit it/replace for tests? | |
| May 16 at 13:37 | comment | added | Firas Abd El Gani | Yes. while trying to reproduce this issue, by plugging & re plugging the power connector frequently, it remains 0W indefinitely. the capacitors have 20V but no current going through. (I even measured an output of the first DC-DC to which VIN_ALW is connected, and showed 0V - at first I thought this has to do with over-voltage protection due to voltage spike, but the voltage never went above 20V). It remains 0W until I replug the power connector several times in order to get the device draw current again. I didn't notice any consistency about when the device get back alive and when it doesn't. | |
| May 16 at 13:27 | comment | added | John Birckhead | Does the lab power supply remain at 0W indefinitely when this occurs? Does this occur when a load is present? When you say the input capacitor voltage is correct, do you man that there is voltage on the capacitors but no current from the supply? | |
| May 16 at 13:23 | comment | added | Firas Abd El Gani | Thank you for the insight! Given that ferrite beads can saturate at a fraction of their RMS current rating, I have a follow-up question. If I add five BLM18KG300TN1D ferrite beads in parallel, would this configuration help in avoiding magnetic saturation when handling a total current of 5A? My understanding is that with five beads in parallel, the current through each bead would be reduced to 1A, which should be well below their saturation current. Is this a valid approach, or are there other factors I should consider to ensure effective noise suppression and prevent saturation? | |
| May 16 at 12:34 | comment | added | Tim Williams | Beware that ferrite beads typically saturate at quite low currents, a fraction of the RMS current rating (which is thermal only, not driven by characteristics). I was not able to find saturation current data on the BLM18KG300TN1. | |
| May 16 at 12:00 | comment | added | Firas Abd El Gani | Yes, but since there are two parallel ferrite beads, each one will deliver maximum 5A. so I assumed there will not be overheating/saturation. what am I missing? | |
| May 16 at 11:16 | comment | added | smajli | BLM18KG300TN1D is rated 5A at 85deg Celcius, and 3.3A at 125deg Celcius. You said your load is at the level of 8 to 9Ams. Aren't ferrite beads overheating? | |
| May 16 at 10:56 | comment | added | Firas Abd El Gani | @smajli Lab power supply shows 20V @ 0 W - which looks like there is high-impedance/open circuit. | |
| May 16 at 10:56 | history | edited | Firas Abd El Gani | CC BY-SA 4.0 |
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| May 16 at 10:46 | comment | added | smajli | What is the character of your 'disconnection'? Physical removal of the power plug? Switched on-off-on? Also: The second (working) circuit has TVS diode. This play significant role in spikes reduction. | |
| May 16 at 10:07 | history | asked | Firas Abd El Gani | CC BY-SA 4.0 |