TPA3122 doesn't work

[Joku]

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?

[picowallspeaker]

Did you check the s-by and the mute pins ?

[killerbobjr]

/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.

[theAnonymous1]

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.

[Joku]

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?

[theAnonymous1]

Originally Posted by Joku

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?

Originally Posted by Joku

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.

[Joku]

Originally Posted by picowallspeaker

Did you check the s-by and the mute pins ?

Just checked it out and SD is high and mute low.

Originally Posted by theAnonymous1

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.

[Joku]

Originally Posted by theAnonymous1

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.

[Joku]

Here's the schematic I used for preamp

[theAnonymous1]

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.