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That pattern is normal for a lot of buck converters. That's what it looks like when they're in PFM (pulse skipping) mode. Try putting some more load, the pulse should be denser.
the feedback pin is also receiving 4v like the output at 7v.
I don't understand. VFB is 4V while VOUT is 7V?
No, when VIN is 8v (sorry not 7v, I made a mistake!), the vout is 4.7v RMS (5.1v top, 4.5v base). bringing the voltage higher just increases it.
The feedback pin is nearly the same as the output.
My only guess so far is that my poorly designed PCB layout is causing noise on the FB pin which in turn makes the step down go crazy. -
Sorry, forgot to give info on the "Screenshots" (Sorry my mac is dumb and can't do FAT32, only exFat! and I have no lan ports near my scope)
https://www.eevblog.com/forum/index.php?action=dlattach;topic=430201.0;attach=2264716;image
Why is C17 missing in this photo? You tried testing it first with it in place right?
Also why does C14 look white, like a low value capacitor? If its 10uF it should be a darker brown color. But I could be wrong.
As you say microscope should help. -
Sorry, forgot to give info on the "Screenshots" (Sorry my mac is dumb and can't do FAT32, only exFat! and I have no lan ports near my scope)
https://www.eevblog.com/forum/index.php?action=dlattach;topic=430201.0;attach=2264716;image
Why is C17 missing in this photo? At least from what I see, hard to tell. As you say microscope should help.
Also why does C14 look white, like a low value capacitor? If its 10uF it should be a darker brown color. But I could be wrong.
It's dark grey! And yes, C14 was missing because I took the picture when testing something, it's back on the board now
Speaking of which I tested everything else and I think i'm getting ready to put an order. (found out I forgot a pullup on the single wire port).
I also have another theory which TBH I don't like, that is during my process of transferring my components to an SMD reel, I misprinted the labels and as a result put another value of capacitor on the BST pin. This means i have to wait longer and pay 25CAD of shipping to LCSC for just another set of every cap I own! I'll go with quality ones this time and not any random cheap ones I find (say Samsung instead of no-name ones)
EDIT: Cap indeed reads 92.5nF which is close enough It's an xr7 50v rated one appearntly!
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So no meters available that can measure capacitance?
Quality or noname is not a huge deal as long as they are X5R/X7R and not Y series. -
I thought my multimeter could only measure in the uF range as it's kind of crappy (AstroAI DM600AR) but it can do nF! yes, it's the correct value.
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Before committing to ordering a new PCB it might be a good idea to investigate why the current PCB is failing.
-The feedback: the feedback can't pick up noise to the extend to make the regulator go crazy because the trace is low impedance. (directly connected to the buck output capacitors.)
-The layout is not perfect but it should work fine.
Other comments:
-NRST pin requires a pull up resistor (10K will do).
-The SWD interface also requires NRST. I don't see NRST going to to the debug header. -
Before committing to ordering a new PCB it might be a good idea to investigate why the current PCB is failing.
-The feedback: the feedback can't pick up noise to the extend to make the regulator go crazy because the trace is low impedance. (directly connected to the buck output capacitors.)
-The layout is not perfect but it should work fine.
Agreed. First thing would be to make absolutely sure the populated buck converter was indeed the right chip, the inductor the right value (and properly sized) and that there was no short or open-circuit.
Also, not sure I understood everything the OP did, but shorting the BOOST and SW pins doesn't sound like a great idea.
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That’s the strange thing, my only other guess is that I damaged a component during soldering….
Me and my friend both spent an entire day looking st the data sheet and could not figure out what was happening… it just behaves the same strange way. Ramping up and down, the frequency changes with the voltage, the vout goes high with VIN.
When I added a 10uF electrolyte cap to the output my power led starting dimming and getting brighter like a heartbeat..
I’ve heard of someone using this IC on a breadboard successfully, so it should work despite a suboptimal layout. I’m tempted to order an overpriced SMD to TH PCB from Amazon to test it further
You can also use the swd without NRST and I thought it has an internal pull up already?
At this point, I’m at a a loss, the only explanation I have is heat damage, or my poor storage (dropped in a 3D printed plastic SMD container.
Capacitors and inductors don’t go bad easily AFAIK so it must be the IC. -
I have used AP6xxxx switching converters in several projects and never had any problem. They work very well. In particular, I've used the AP64501, it's rock-solid.
Yes your layout should be fine, unless we missed something.
Possibly you had damaged or non-genuine chips. I don't know. From your initial schematic, I think you had placed output capacitors after a fuse, which wasn't such a good idea as it would add some series resistance, but apart from that, I don't know. Actually given the package those converters come in, you could re-prototype just the step-down part on a piece of proto board, just to make sure.
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I have used AP6xxxx switching converters in several projects and never had any problem. They work very well. In particular, I've used the AP64501, it's rock-solid.
Yes your layout should be fine, unless we missed something.
Possibly you had damaged or non-genuine chips. I don't know. From your initial schematic, I think you had placed output capacitors after a fuse, which wasn't such a good idea as it would add some series resistance, but apart from that, I don't know. Actually given the package those converters come in, you could re-prototype just the step-down part on a piece of proto board, just to make sure.
Guess what, this was already my second attempt, but I made a third PCB in desperate before going to bed (Only the step-down components,) and it works perfectly. It has 10mv pk-pk output ripple under a 10ohm load, stable, even voltage even after drastically changing from 7v to 17v. This is with one 22uF Cap not two!
so now my question is, how on earth did I manage to burn through 3 ICs each time, despite using Low temp solder?! is it my storage method (dumping them in a PLA 3d printer container) ESD from my body (I do put the IC under my finger to double check the alignment before putting it on the board) or perhaps just bad luck?!!! the components are from LCSC.
Were they soldered fine and burned on a specific start condition? I do have to note that my pencil does make my LEDs glow as I use it to solder, but I assume it's such a low voltage that it'd not matter. I did have to rework a pin on my PCB all 3 times, including this one. The only thing I did differently was my 195c (vs 250c) temp, and discharging my body with ground before starting. I also did use another power supply with my pinecil (140w capable)
are these ICs just super heat sensitive?!
This little white LED makes me so happy...
I tried to kill it by sparking the input (suddenly connecting the alligator like I did first instead of connecting, then turning on my PSU) and a few other stuff but it didn't die.
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> I do have to note that my pencil does make my LEDs glow as I use it to solder, but I assume it's such a low voltage that it'd not matter.
It's matter a lot! You probably burned out your IC with this pencil. Glowing LED mean that tip of your pencil radiate high frequncy voltage or just under high ESD level. Ideally soldering tip should be grounded. -
Well I guess I have an excuse to treat myself to the auxin T420 now xD
But jokes aside I’ll try to do some research to find something that’s grounded and cheap. I like the modern cartridge style ones a lot
EDIT: Excuse me being a beginner, but I measured 55v AC relative to ground on my pinecil's tip?!!! what... how could that be happening?
I guess I could also start using a power bank instead. or use the DC plugin. -
Well I guess I have an excuse to treat myself to the auxin T420 now xD
But jokes aside I’ll try to do some research to find something that’s grounded and cheap. I like the modern cartridge style ones a lot
EDIT: Excuse me being a beginner, but I measured 55v AC relative to ground on my pinecil's tip?!!! what... how could that be happening?
I guess I could also start using a power bank instead. or use the DC plugin.
That's not unusual with many of the cheap soldering stations and can cause damage. Note that I've read similar issues with the T420 you're mentioning, so you should definitely look for reviews before buying.
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One remark on the ground vias, as long as you're not using exotic technologies like copper-filled vias, packing them so dense is not necessary and increases both the electrical and thermal impedance in your ground plane. Not that it makes any difference in this particular case, but it's something to keep in mind for other designs where it will be detrimental.
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The auxin T420 looks like a good soldering iron to me. The tip is not directly connected to earth but trough a high value resistor.
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Well I guess I have an excuse to treat myself to the auxin T420 now xD
But jokes aside I’ll try to do some research to find something that’s grounded and cheap. I like the modern cartridge style ones a lot
EDIT: Excuse me being a beginner, but I measured 55v AC relative to ground on my pinecil's tip?!!! what... how could that be happening?
I guess I could also start using a power bank instead. or use the DC plugin.
That's not unusual with many of the cheap soldering stations and can cause damage. Note that I've read similar issues with the T420 you're mentioning, so you should definitely look for reviews before buying.
Oh shoo, I chose that one over T320 purely because it has an isolated power supply. What soldering iron would you recommend? That Iron is pretty much the upper limit of my budget, I was going to grab a miniware mhp50 but this seems more important TBH.
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One remark on the ground vias, as long as you're not using exotic technologies like copper-filled vias, packing them so dense is not necessary and increases both the electrical and thermal impedance in your ground plane. Not that it makes any difference in this particular case, but it's something to keep in mind for other designs where it will be detrimental.
Oh that's strange... I was expecting the absolute opposite! Why does this happen? -
The auxin T420 looks like a good soldering iron to me. The tip is not directly connected to earth but trough a high value resistor.
is the resistor a bad or good thing? Why would they use a resistor?
Also I'm open to any recommendations, the upper limit of my budget is the TD420. So I'd like something in the same price range. Maybe I should start a new post in the equipment subforums. -
EDIT: Excuse me being a beginner, but I measured 55v AC relative to ground on my pinecil's tip?!!! what... how could that be happening?
I guess I could also start using a power bank instead. or use the DC plugin.
You can either use a power bank, DC plug (assuming your DC source is earthed, most are not), or earth the unit as shown in this photo:
https://www.aliexpress.us/item/3256806229994814.html
Shame they don't have a clear explanation of this in the wiki, just a short mention at the bottom: https://wiki.pine64.org/wiki/Pinecil#History_of_Pinecil_Changes -
EDIT: Excuse me being a beginner, but I measured 55v AC relative to ground on my pinecil's tip?!!! what... how could that be happening?
I guess I could also start using a power bank instead. or use the DC plugin.
You can either use a power bank, DC plug (assuming your DC source is earthed, most are not), or earth the unit as shown in this photo:
https://www.aliexpress.us/item/3256806229994814.html
Shame they don't have a clear explanation of this in the wiki, just a short mention at the bottom: https://wiki.pine64.org/wiki/Pinecil#History_of_Pinecil_Changes
yeah, it all sounds even more clunky and annoying than it already is, but 320CAD is a LOT of money to drop on an iron, I think I'll hopefully manage to resist and wait until I come into my senses again. -
Hakko FX-888DX is ~170CAD and won't zap your chips.
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Yeah but at that point I might shell 80 extra cad for a nice JBC clone, I can’t stand those old school irons that take ages to heat up or choke on ground planes!
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To be fair, I think the Aixun station I had seen a review of, and which mentioned a relatively high DC voltage on the tip, was a lower-end model and not this T420D, which claims to be isolated. So possibly this one is clean.
Thing is, while cheaper than a genuine JBC, it's already a sizable amount of money for a clone. You can get a decent Weller soldering station for that price.
I do second the greatness of the JBC tips though. Fantastic stuff.The C210 cartridges heat up to over 300°C in under 3 s. Crazy. So with JBC stations and all decent clones, the station goes into a "sleep" mode as soon as you put the tip back into its stand, and usually the sleep mode regulates the temperature to around 150°C (and finally powers it off after a user-defined delay), so when you pull it out of the stand, it gets back to temperature in like 1 s, while prolonging its lifetime significantly compared to keeping it at > 300°C for hours during a working day.
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Quote
is the resistor a bad or good thing? Why would they use a resistor?
The soldering tip is floating which is good. Why you'll need that:
1. The tip will not cause a short to earth when soldering something onto a powered board powered by an earthed power supply. (That will happen sooner or later in the form of doing just a quick fix. Let's put 10 K here or there. Meanwhile you forgot to switch off the power.)
2. The resistor limits ESD discharge currents to safe levels.
4. The tip is always at earth potential and can not be a source of ESD.
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Quote
is the resistor a bad or good thing? Why would they use a resistor?
The soldering tip is floating which is good. Why you'll need that:
1. The tip will not cause a short to earth when soldering something onto a powered board powered by an earthed power supply. (That will happen sooner or later in the form of doing just a quick fix. Let's put 10 K here or there. Meanwhile you forgot to switch off the power.)
2. The resistor limits ESD discharge currents to safe levels.
4. The tip is always at earth potential and can not be a source of ESD.
Ooh that makes sense
I think that I'll just run a single thin ground wire to my pinecil for now, lets hope it won't disconnect mid-soldering!
also I have a weller WESD51, I am tempted to order it fresh tips but that'd be 30$. I think i'll deal with this or a power bank and pinecil until I can make sure that it's a good investment, or until I give up and order it at 3am. I also am tempted to try my luck at DIYing a PCB but gosh, I DIY everything... I think I need a break xD Also the td420 has really nice reviews, but I do get the hate on a product like this tbh, the issue is that.... 800cad fo a genuine one is insane to me! and i'm not a profassional.
Thank you all