MCP1640 boost regulator outputting 8 volts?!

[quote author=Jack Christensen link=topic=244484.msg1751125#msg1751125 date=1401828027] Have a spare MCP1640? I might just try replacing it. [/quote] Aaaand... Nope. Didn't help. What the actual... Edit: And neither does connecting another inductor in pararell (esr drops, inductance stays in limit, but nope) or removing the filtering capacitor. Edit 2: ANGHHTHHTHT!!!!!!!!!!! I CHANGED THE RESISTOR! NOW IT SHOULD GIVE EFFIN 3.3 VOLTS, BUT GUESS WHAT?!?! IT'S EVEN WORSE! 8 volts all the way. omg WHAT IS GOING ON WHAT IS GOING ON WHAT-IS-GOING-ON WHY WHY WHAT

thegoodhen: Continuity tests ok, capacitors are there, the inductor seems fine, plus I have used the exact one before and it worked just fine.

You used the same inductor before? For what? With an MCP1640, or for something else? Got a part number or link to the inductor?

[quote author=Jack Christensen link=topic=244484.msg1755308#msg1755308 date=1402077290]

thegoodhen: Continuity tests ok, capacitors are there, the inductor seems fine, plus I have used the exact one before and it worked just fine.

You used the same inductor before? For what? With an MCP1640, or for something else? Got a part number or link to the inductor?

[/quote]

http://www.tme.eu/cz/Document/76aa6f2e4800aa20668de5274e067fd8/dla_a.pdf

This one-it has worked with this chip before. The esr is slightly higher than recommended, but even when I tried 2 in paralell, still no luck.

thegoodhen: http://www.tme.eu/cz/Document/76aa6f2e4800aa20668de5274e067fd8/dla_a.pdf

This one-it has worked with this chip before. The esr is slightly higher than recommended, but even when I tried 2 in paralell, still no luck.

I'd say that at 1?, ESR is more than slightly higher than recommended. It's high at least by a factor of 3 to 5, and it's not hard to find inductors with 1/10 of the ESR. It's current rating is pretty low too, only 190mA. MCP1640 datasheet says inductor current can be as high as 800mA.

Here is the part I use, although I've also tried several other quite similar parts with essentially identical results. ESR is 0.07? and saturation current is 2A.

You say it has worked in the past, so I cannot argue, but I do wonder what else might be different. I'd think an inadequate inductor might work fine at no load or small loads (e.g. 1-2mA) but then I would expect output voltage to fall if too much current is drawn. At least that has been my experience. So I'm still scratching my head.

Hi, have you measured the values of your resistors? Not all smd resistors are manufactured equal, I have had a spool of 3k9 smd in a production run that measured okay out of the spool, BUT jumped to over 10K when you soldered them in. Got suspicious when the conductive ends of components started PEALING off the component body.

Tom....... :) PS, have you checked with the scope , your input power trace? If scope shows 6V with 0.1V ripple, why does DMM show 8V, DMM battery low, try another DMM. I agree 0.1V is a bit high.

Edit, your PCB pattern has a connection to pin1 that goes from a relatively wide trace to a very narrow, have you tried making that thin trace bigger, even with a bit of wire, it will be introducing significant series resistance I bekieve.

TomGeorge: Not all smd resistors are manufactured equal, I have had a spool of 3k9 smd in a production run that measured okay out of the spool, BUT jumped to over 10K when you soldered them in. Got suspicious when the conductive ends of components started PEALING off the component body.

Hope you sent 'em back. Sounds like defective material, assuming the soldering process was within spec.

TomGeorge: Hi, have you measured the values of your resistors? Not all smd resistors are manufactured equal, I have had a spool of 3k9 smd in a production run that measured okay out of the spool, BUT jumped to over 10K when you soldered them in. Got suspicious when the conductive ends of components started PEALING off the component body.

Tom....... :) PS, have you checked with the scope , your input power trace? If scope shows 6V with 0.1V ripple, why does DMM show 8V, DMM battery low, try another DMM. I agree 0.1V is a bit high.

Edit, your PCB pattern has a connection to pin1 that goes from a relatively wide trace to a very narrow, have you tried making that thin trace bigger, even with a bit of wire, it will be introducing significant series resistance I bekieve.

Sorry about the confusion. I sometimes get as close as 5V, sometimes 8. It depends on the load. The DMM measured the same value as my scope at the time I checked it. You could be right about the trace. I have etched 2 boards, one of which didn't turn out really well (made a mistake in the design). I will try to build just a standalone DC/DC converter board out off the first one. Due to the high values of the resistor, there might be a flux residuum causing a problem there somewhere (leakage current). I mean, I've cleaned the board, but one never knows.

Exactly; The worst ESR out of the inductors the datasheet recommends is about 0.5. Now that is for full power, 5v, 300ma. “My” ESR is 2 times worse (now the same, 2 inductors in pararell, inductance halves, still in limit), but the current I am trying to draw is <30ma.

I’ve had success powering 36 leds with this inductor; I had to use huge caps for bypassing, but it worked. (Yea, yea. I know. Not a sensible design.) That was about 300ma, pushing it to the limit. Only problem was a voltage drop, which I had to resolve with the aforementioned bypass caps.

I am starting to think it’s either too small ground return path or leakage currents. I will build a DC/DC converter with those parts. A standalone one, similar layout. We’ll see.

Okay. The EXACT SAME CHIP (not just the same number), placed deadbug style on ABSOLUTELY RIDICULOUS layout, soldered with no flux works. So… Am I going crazy? Or is it leakage?

thegoodhen:
Okay. The EXACT SAME CHIP (not just the same number), placed deadbug style on ABSOLUTELY RIDICULOUS layout, soldered with no flux works. So… Am I going crazy? Or is it leakage?

Back to the PC board then. It’s either layout or an error (design or manufacturing) on the board. What software was used to create the board? I did not check it 100% against the schematic (that’s a job for software).

I doubt that residual flux will cause significant leakage, especially on a newly assembled board. Easy enough to remove that possibility though.

I am using Arduino 3.3v regulator as a power supply at the moment.

Your power supply may involve multiple switching regulators connected in series, each having its own startup, switching and loading characteristics. For example, with the Arduino Due you would have:

LM2734Y (+5V) ===> NCP1117ST33T3G -3V3 ===> MCP1640

Try testing if your circuit works as intended with battery power to determine if the power source is the problem.

[quote author=Jack Christensen link=topic=244484.msg1756140#msg1756140 date=1402142105]

thegoodhen: Okay. The EXACT SAME CHIP (not just the same number), placed deadbug style on ABSOLUTELY RIDICULOUS layout, soldered with no flux works. So... Am I going crazy? Or is it leakage?

Back to the PC board then. It's either layout or an error (design or manufacturing) on the board. What software was used to create the board? I did not check it 100% against the schematic (that's a job for software).

I doubt that residual flux will cause significant leakage, especially on a newly assembled board. Easy enough to remove that possibility though. [/quote]

Hello! Sorry about the misconception. When I've changed the resistor for lower output voltage, I have actually replaced it with a bad one. (3 orders of magnitude lower, my bad). The board is newly assembled, but home etched. I have replaced the resistor with one that would give me ~3.3v out. While doing so, I have noticed there is a bit of flux residuum between the 2 pins. I've got rid of that. It now gives 3.4-3.7v. That is > vin and relatively close to expected voltage. Must've been the flux. It's Pro'skit solder paste. A warning comes with it. "This solder paste is not suitable for the soldering point on Integrated Circuit or high voltage (frequency/power) You are suggested to clean the soldering point by ethyl alcohol after using in order to avoid the possible short situation."

So... yea.

thegoodhen: "This solder paste is not suitable for the soldering point on Integrated Circuit or high voltage (frequency/power) You are suggested to clean the soldering point by ethyl alcohol after using in order to avoid the possible short situation."

Wow. I'd sure be ditching that stuff immediately. Maybe it could be used for copper plumbing.

FWIW, my favorite

[quote author=Jack Christensen link=topic=244484.msg1756527#msg1756527 date=1402165695]

thegoodhen: "This solder paste is not suitable for the soldering point on Integrated Circuit or high voltage (frequency/power) You are suggested to clean the soldering point by ethyl alcohol after using in order to avoid the possible short situation."

Wow. I'd sure be ditching that stuff immediately. Maybe it could be used for copper plumbing.

FWIW, my favorite [/quote]

I gotta say It works really well-the consistency of the solder gets really really nice and it doesn't stink... But yea, it must've been the cause of the issue... I've desoldered the resistor, slid my soldering iron between the 2 pins, it made "vssschcchhchch" and it works like a charm now. Thanks for the tip and ongoing support though!

Glad you got it solved, that was a tough one! Be sure to let me know if you ever manage to get 350mA out of a MCP1640 (as advertised by the datasheet) -- this is the only way it's disappointed me. I can get reasonably close to that, but only if I ramp the load up slowly. But it won't start properly (never gets up to voltage) into a load that needs more than about 150-175mA. Anyway it works well for applications that need less current than that.

[quote author=Jack Christensen link=topic=244484.msg1756604#msg1756604 date=1402170781] Glad you got it solved, that was a tough one! Be sure to let me know if you ever manage to get 350mA out of a MCP1640 (as advertised by the datasheet) -- this is the only way it's disappointed me. I can get reasonably close to that, but only if I ramp the load up slowly. But it won't start properly (never gets up to voltage) into a load that needs more than about 150-175mA. Anyway it works well for applications that need less current than that. [/quote] Haha, yea! Thnaks If it wasn't, I wouldn't bother these forums with it. I am self taught and I don't like asking for advice-I usually want to solve everything on my own. I have sort of managed that; you have to connect it to a huge bypass capacitor, wait a bit and then connect the load...

Edit: In my case (~350mA): 100uF+2*4700uF

Edit2: I use the version that connects Vin to Vout when not enabled. So the caps get charged a bit before it starts; the transition is then not so hard, it doesn't go into full short circuit.

I was beginning to wonder about that, and it’s one thing I hadn’t tried, was to make sure the input power supply was robust enough. A pair of fresh AA alkaline cells evidently aren’t good enough. Thanks, I’ll play with it!

It’s Pro’skit solder paste. A warning comes with it. “This solder paste is not suitable for the soldering point on Integrated Circuit or high voltage (frequency/power) You are suggested to clean the soldering point by ethyl alcohol after using in order to avoid the possible short situation.”

Hi, a poltergeist in the machine!!!

Good to hear you got it sorted, I’m sorry but I don’t know of any good hair restorer.

Tom… :slight_smile:

[quote author=Jack Christensen link=topic=244484.msg1756649#msg1756649 date=1402173328] I was beginning to wonder about that, and it's one thing I hadn't tried, was to make sure the input power supply was robust enough. A pair of fresh AA alkaline cells evidently aren't good enough. Thanks, I'll play with it! [/quote] Hi, no problem. I believe this is the solution-at least, it worked for me when I was powering 12 RGB LEDS. Although I didn't have all of them on at the same time (with all colors) and I am not sure about the actual current flowing through there, they sure do light up brightly, so it should be giving out a lot of juice. I actually had problems with it before I've added the huge caps and they solved the issue, so it may be the same for you.

TomGeorge:

It's Pro'skit solder paste. A warning comes with it. "This solder paste is not suitable for the soldering point on Integrated Circuit or high voltage (frequency/power) You are suggested to clean the soldering point by ethyl alcohol after using in order to avoid the possible short situation."

Hi, a poltergeist in the machine!!!!!!!!!

Good to hear you got it sorted, I'm sorry but I don't know of any good hair restorer.

Tom.... :)

Haha, thanks! Yea, works now. Seems like I overengineered it quite a bit, too. It's a clock-and I've done so far with energy saving that the batteries will die due to their shelf-life sooner then they will completely discharge. :D The estimated battery life, self-discharge included is ~25 years. Oh well. :D