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Old 26th April 2011, 03:04 PM   #1
Joku is offline Joku  Finland
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Default TPA3122 doesn't work

I recently made a TPA3122 pcb myself. However, when I try to use it, I just hear clicking sounds from the speakers. Also, when inspecting it with oscilloscope, looks like it's trying to start (voltage at output goes up for a moment and then goes down a few times in a second). The schematic is basically directly from the datasheet.

Any ideas?
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File Type: jpg TPA3122_pcb.jpg (77.1 KB, 219 views)
File Type: jpg TPA3122_schematic.jpg (42.2 KB, 207 views)

Last edited by Joku; 26th April 2011 at 03:14 PM.
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Old 26th April 2011, 03:40 PM   #2
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Did you check the s-by and the mute pins ?
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Old 26th April 2011, 04:01 PM   #3
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/SD needs to be connected to VCC through a pullup resistor, 10K or so. Also, AGND and PGND are not connected to each other and you don't have output DC blocking caps. Were you trying to use a split supply? That's not going to work. The TPA3xxx chips only work with a single supply.
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Old 26th April 2011, 04:06 PM   #4
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Where are the output blocking caps? If you aren't using any, then that's your problem.

Also, where does AGND connect to PGND?

EDIT: "Ninja'd" by killer, as the kids say.
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Old 26th April 2011, 05:30 PM   #5
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I'm using it in bridged mode, so no output capacitors are needed. AGND and PGND are connected to each other at power supply (I'm using two of the chips to make a stereo amp), should they be connected on the PCB instead?

Also, do you have to use a resistor between VCC and /SD?

Last edited by Joku; 26th April 2011 at 05:39 PM.
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Old 26th April 2011, 05:43 PM   #6
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Quote:
Originally Posted by Joku View Post
I'm using it in bridged mode, so no output capacitors are needed. AGND and PGND are connected to each other at power supply (I'm using two of the chips to make a stereo amp), should they be connected on the PCB instead?
That's not the problem then.

How are you bridging them? Are you running a balanced signal?

Quote:
Originally Posted by Joku View Post
Also, do you have to use a resistor between VCC and /SD?
I don't on my working boards.

BTW, the 4.7k resistors on the output aren't needed if you are running it bridged. They are only there to drain residual voltage on the blocking caps when the amp is powered off.

Last edited by theAnonymous1; 26th April 2011 at 05:48 PM.
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Old 26th April 2011, 05:58 PM   #7
Joku is offline Joku  Finland
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Quote:
Originally Posted by picowallspeaker View Post
Did you check the s-by and the mute pins ?
Just checked it out and SD is high and mute low.

Quote:
Originally Posted by theAnonymous1 View Post
That's not the problem then.

How are you bridging them? Are you running a balanced signal?
Yeah, I turned the normal stereo signal into two balanced signals with an inverting opamp circuit. It has unity gain, so the plus input is straight from the potentiometer while the minus input is from the opamp.

Last edited by Joku; 26th April 2011 at 06:00 PM.
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Old 26th April 2011, 06:10 PM   #8
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Quote:
Originally Posted by theAnonymous1 View Post
BTW, the 4.7k resistors on the output aren't needed if you are running it bridged. They are only there to drain residual voltage on the blocking caps when the amp is powered off.
Hmm, the bridged output schematic in the datasheet had them, I don't know why.
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Old 26th April 2011, 07:03 PM   #9
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Here's the schematic I used for preamp
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File Type: jpg TPA3122_preamp.jpg (29.7 KB, 183 views)
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Old 26th April 2011, 07:08 PM   #10
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Have you tried playing the amp without the pre-amp circuit attached?

Try connecting one of the inputs to ground and playing a single ended signal through the other input. Still connect the load to both outputs just like BTL though.

Only half the bridge will play, the other half will just provide DC bias so you don't have to install blocking caps. That will at least tell you if the pre-amp circuit is causing a problem or not.
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