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Old 26th April 2011, 08:48 PM   #11
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Originally Posted by Joku View Post
AGND and PGND are connected to each other at power supply
That's too far away. Your star ground should be at the chip, otherwise you may get secondary oscillations.
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Also, do you have to use a resistor between VCC and /SD?
Yes. That requires a current limited input and connecting directly to VCC is most likely causing your instability -- the chip heats up, shuts down, recovers, heats up, shuts down, etc.
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Old 26th April 2011, 09:45 PM   #12
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I added the resistor and a jumper which connects the grounds at PCB. Now it seems to be running when I have nothing connected to inputs, but if I touch either of the inputs with anything (even with a piece of metal that is connected to nothing), it stops.
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Old 27th April 2011, 04:43 AM   #13
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I just noticed your GAIN0 pin is connected directly to VCC. Again, it's a current limited input -- connect to VCC via a 10K resistor. Better yet, cut the trace and connect GAIN0 to ground for 20dB gain which gives you lower noise and distortion.
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Old 27th April 2011, 06:10 AM   #14
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Yes. That requires a current limited input and connecting .directly to VCC is most likely causing your instability -- the chip heats up, shuts down, recovers, heats up, shuts down, etc.
Not really true. I have it connected directly to VCC on all of my boards and they work perfectly fine. You only need the resistor if you plan on using the shutdown function.
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Old 27th April 2011, 08:11 AM   #15
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1. Most likely the TPA3xxx chips are built on MOS. The TI docs don't list breakdown voltages for any of the inputs, so there's a possibility some inputs are bipolar, especially noting that the max VCC is 36V. A 10K resistor eliminates any possibility that tying an input to VCC will current damage it.

2. There's 250KHz (give or take several KHz) ripple on VCC. If the inputs are MOS gates, that ripple feeds through. A 10K resistor will help filter that out. If you want to be really anal, you could put decoupling caps on all the logic inputs tied to VCC to eliminate any possibility of ripple feeding through.
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Old 27th April 2011, 08:25 AM   #16
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Actually TI's datasheet does say that the allowed voltage for logic inputs is from -0.3 to Vcc +0.3..

I guess I could try adding a resistor to gain pins also, it just sounds unlikely that the problem is caused by it as others haven't used the resistors and got it to work fine.
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Old 27th April 2011, 12:03 PM   #17
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Ah, you're right. I skipped right past it. That'll teach me not to speed read.

Your C3 and C4 are mono caps, yes? Those should absolutely be low esr, non-inductive caps.

Have you tried to see if it runs in single ended mode yet? Attach DC blocking caps to the output terminals and then to speakers, and attach the inputs to L and R.
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Old 27th April 2011, 12:54 PM   #18
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C3 and C4 are plastic capacitors, I don't know if they are low-esr or other special capacitors.

I haven't tried to run them in single ended mode, but I don't think it matters as the chips go offline if you even touch the inputs with anything, whether or not there is a load.
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Old 27th April 2011, 01:32 PM   #19
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Single ended or BTL shouldn't matter.

I've built quite a few different PCB iterations using this IC and they have all worked (and I'm no professional by any means). Some had hum from bad grounding, but they did work.

I'm guessing it's either a layout problem or a capacitor problem. I used low ESR X7R ceramics for all the low value caps. You should try switching C3/C4 to >220nF X7R as close to the pins as possible.

I also used 2 layer PCB utilizing the second layer as a ground plane. Not sure if that played any role in my success rate or not.
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Old 27th April 2011, 01:53 PM   #20
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I used an electrolytic capacitor as the 10 capacitor, is that fine?
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