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A Simple TPA3250 BTL Board
A Simple TPA3250 BTL Board
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Old 27th October 2020, 07:22 PM   #11
matt_garman is offline matt_garman  United States
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Join Date: Feb 2008
Location: Chicago, Illinois, USA
A Simple TPA3250 BTL Board
@joensd - thank you for the assistance! The KiCad files are attached to this message. Let me know if you want the BOM or any other supporting materials.


Quote:
Originally Posted by joensd View Post
Layout/implementation/GND routing can still cause the chip to oscillate and generate excessive heat (although it works).
Agreed, though I think I'm going to focus on solder issues first...


Quote:
Originally Posted by joensd View Post
Chances are also that the pad is "cold" soldered to the PCB and there is a huge thermal resistance in that spot. Did you use solder paste?

Can you visually make out if the connection of the thermal pad is good or not?
I did use solder paste, Mechanic XG-Z40 Sn63/Pb37.

I can't tell by looking if the thermal pad connection is good or not, at least not with my naked eye. I think we have a USB microscope somewhere, I think that would be helpful here!


Quote:
Originally Posted by joensd View Post
How hot does the chip get when it idles? (no input signal)
Does it work properly when you play music with little volume?
I've thus far only done the one test. But based on that: I didn't really check the temperature when idle. Most of the testing was done at fairly low volume, and it sounded OK. During this relatively quiet playback, the IC temperature was such that I could touch it, but only for maybe five seconds before it got uncomfortable.

When I turned the music up a bit, enough to trigger the clip/over temp indicator, the chip was too hot to touch even for a second.

I do have an IR thermometer, wishing now I'd have used that, rather than relying on touch!


Quote:
Originally Posted by joensd View Post
In the forelast picture on the top right I see a big blob of solder, right?
The cap doesnīt look shorted but watch out for solder pellets or similar and inspect the whole board.
I don't think those caps are shorted. The angle of the picture makes it look like there's a big blob of solder between them. But there's actually a fairly comfortable gap between them. The one cap was soldered by hand, since it did move too much during "frying", and initially was touching the other one. FYI, those are the 33nF bootstrap caps.


Quote:
Originally Posted by joensd View Post
is there a short between the IC pins?
in a more closer look I also see lots of solder pellets under the IC
which is somewaht expected when using the "pan-fry-method" ;-)
Those close-up pics of the chip pins were taken using my phone with 4x zoom - those solder pellets are not visible to my naked eye!

But I agree, with the zoomed-in pics, the chip pin soldering does look a little sketchy.

I'm thinking I can check those chip pins for shorts. If there's an obvious short I'll try to touch it up by hand. If I don't see an obvious problem, I guess I'll try to remove the tpa3250 and "re-fry" it.

Thanks again!
Attached Files
File Type: zip tpa3250_kicad_20201027.zip (1.02 MB, 3 views)
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Old 27th October 2020, 08:05 PM   #12
joensd is offline joensd  Germany
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Join Date: Dec 2001
Location: Germany
Quote:
@joensd - thank you for the assistance! The KiCad files are attached to this message. Let me know if you want the BOM or any other supporting materials.
Youīre welcome. Thanks for the files!
Quote:
I did use solder paste
Thatīs good because usually when the amount is right the soldering works out quite well; even with a "hot plate".
Quote:
I think I'm going to focus on solder issues first...
Yes, thatīs what I would do. Maybe you find that microscope.
Otherwise look for solder pellets or excessive solder that goes beyond its pad.
From the side you should be able to judge if the IC sits flat on the pad.
Considering how much solder you applied you should also know if it has a good connection.

Take your time. "Refrying" the chip can cause more problems than it solves...
All of the solder and parts will swim; vias can tear; the chip can take damage...


If itīs really the OTW the chip should "measure" about 125° which is substantial.
Iīd expect maybe 1W idle dissipation with very low volume and 24V-PSU but that causes not even a rise of ~10K. (Junction-to-board thermal resistance ~ 6.5K/W). You should measure the idle dissipation and note voltage&current.

Did you check all the supply-voltages? Whatīs your main supply-voltage?
An oscilloscope would be great of course to see if thereīs oscillation.
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Old 27th October 2020, 08:12 PM   #13
joensd is offline joensd  Germany
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Join Date: Dec 2001
Location: Germany
If you find that scope or use your phone to inspect the board,
donīt forget to check any solder joints at the SMD-parts.
This one looks for example doesnīt look too nice.
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File Type: jpg tpa3250_ic_pin_solder_detail_1_20201025_edit2.jpg (528.6 KB, 63 views)
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Old 13th November 2020, 02:27 PM   #14
matt_garman is offline matt_garman  United States
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Join Date: Feb 2008
Location: Chicago, Illinois, USA
A Simple TPA3250 BTL Board
I just set it up again, this time with better testing tools.

When I "cranked" the music, enough to get the CLIP led to trigger, I measured the temperature of the top of the tpa3250 IC with my IR thermometer: about 32.3 degrees C (90 degrees F). The IR thermometer said about 38 degrees C (100.4 F) on the PCB right next to the tpa3250 IC.

It's a cheap/old IR thermometer, so I doubt it's accuracy is all that great. And I'm assuming the actual circuitry of the chip is probably warmer than the plastic package. And FWIW, to the touch, the IC feels hotter than the PCB.

I put my DMM in current measuring mode, and put the leads in series with the +24V wire that goes to the amp board (PVDD). The current danced around quite a bit with music playing. I watched it for a while with the volume up (enough to trigger the CLIP light), and the max I saw was about 750 mA. Typically though it stayed under 300 mA.

At idle, I measure about 40 mA on +24V line.

At idle, I also measured the 12V and 3.3V rails (between my power supply PCB and the amp board). On the 3.3V rail, at idle, I read about 11 mA. I'm pretty sure this is just used as a reference voltage for the RESET pin, and also the power-on LED.

Now, when I measured the 12V rail at idle, I'm actually seeing about 101 mA. This seems too high to me. Note: that's with my DMM in DC Amps measuring mode; if I switch to DC milliamps mode, it reads 0.90 mA, which is way too low.

To be clear, all the above measurements were done with the ammeter in series between the different PSU rails (of my PSU PCB) and the amp board.

Lastly, I measured the current between my multi-rail PSU PCB and the main AC-DC power supply (a Meanwell EPP-200-24 SMPS). At idle, I measured 140mA.

In terms of physical inspection: I did find that USB microscope, but it's a cheap one, and I didn't have much luck with it. My wife's phone's camera actually does 10x zoom, and I found that to be usable. I spent some time with rubbing alcohol, cleaning up all the "blobs" left over from the soldering process. It certainly looks nice and clean. All the connections look reasonable to me. The TPA chip itself does seem to have a tiny gap between it and the PCB - not enough to let any light in though, maybe half the thickness of a hair. It's just barely not completely flush to the PCB.

So I'm not sure. My thoughts are that the 12V current draw looks suspicious; and I still haven't ruled out a poor solder connection between the IC and PCB.
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