PCB layout for TDA8920BJ wanted - diyAudio
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Old 16th April 2006, 12:13 AM   #1
Primoz is offline Primoz  Slovenia
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Default PCB layout for TDA8920BJ wanted

I have problems with my TDA8920BJ (non-smd version). At about 10W of output power overcurrent protection starts to work. I've tried almost everything except changing the PCB and I think this is the problem. I have designed single sided PCB and I had a lot of compromises to make (capacitors are not close enough to chip, output inductors are not shielded and are close to inputs...).

I would be very grateful if somebody could give me PCB layout which was tested and works, because I have spent too much time designing and making PCB-s, that dont work (5 pieces).

Layout can be double sided.

If anyone wants I can attach my layout if I can find it. Last time I was designing PCB was almost a year ago, then I gave up working with this IC-s and I started again this week

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Old 16th April 2006, 12:32 AM   #2
BWRX is offline BWRX  United States
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Post the layout and we might be able to help you find a problem.
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Old 16th April 2006, 12:52 AM   #3
Primoz is offline Primoz  Slovenia
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PCB .jpg, edited with MS Paint
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File Type: jpg tda8920bj.jpg (72.5 KB, 1917 views)
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Old 16th April 2006, 01:04 AM   #4
Primoz is offline Primoz  Slovenia
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zipped PCB .brd (for Eagle users)

sorry for the strange name of file . Only first four and last six letters have some meaning (in english amp.....finished)
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File Type: zip ojac236fskoncan.zip (7.4 KB, 562 views)
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Old 16th April 2006, 03:16 AM   #5
BWRX is offline BWRX  United States
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Can you give us any details on the supply you're using? What are the rail voltages unloaded and while the amp is putting out around 10W?

That chip has a bunch of protection provisions. It might not necessarily be the over current protection that is causing your amp to cut out.
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Old 16th April 2006, 11:46 AM   #6
Primoz is offline Primoz  Slovenia
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Im using homemade switching power supply which has regulated both rails. Voltage is +/- 25V. I measured the voltages with load of 200W but they stay the same

I tried with standard supply (trafo, greatz, two capacitors) but the problem stays the same

At the picture is top view of finished PCB.

At left are air inductors, but I tried also with toroide inductors from old computer power supply, and with some other inductors, but problem was always the same
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Old 16th April 2006, 11:52 AM   #7
Primoz is offline Primoz  Slovenia
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Other side
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Old 16th April 2006, 01:44 PM   #8
BWRX is offline BWRX  United States
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The datasheet mentions something about a stabilizer output voltage (the STABI pin) and that it should be around 12V typical with a minimum of 11V and a max of 15V. How does the STABI voltage look on your amp unloaded and when putting out 10W?

Since you said the amp does the same thing with both types of supply, you're probably right that the overcurrent protection is being tripped because of output voltage and current spikes due to the PCB layout.

Do you have access to an oscilloscope to probe the pwm outputs and see exactly what's happening as you increase the output power? That's really the only way to tell for sure, unless you want to try the AM radio test. Bringing an AM radio in the vicinity of your amp will basically kill its reception if you're having EMI issues due to layout.
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Old 16th April 2006, 02:01 PM   #9
Eva is offline Eva  Spain
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How do you know that these air inductors are of the right value? A too small inductor value will trip the overcurrent protection due to increased current ripple. Also, you should keep these air-cored inductors away from the PCB.

Also, how did you get these ICs? The datasheet that I have doesn't even seem to tell about that package option!
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Old 16th April 2006, 02:24 PM   #10
BWRX is offline BWRX  United States
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Eva, you can the most recent datasheet here: http://www.semiconductors.philips.co...TDA8920B_2.pdf

The inductors may not be spot on, but they certainly look to be more than 15uH.

Also, it's hard to tell from the photo, but in some areas it looks like the soldered lands are close to shorting out.
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