tlv320dac3100: Class D short constantly set

Matthew Harlan

Other Parts Discussed in Thread: AM3356, TLV320DAC3100

Hello All

I am in the midst of hardware checkout for a new product using an AM3356 and tlv320DAC3100 connected via McASP0.

We are using the mainline 3.17 kernel driver for the aic31xx family of codecs with minor patches.

I've successfully configured ALSA and the SoC drivers, and I can get proper clocking from the DAC3100 as master, and I get good audio from the HP driver with proper control via the ALSA controls.

My problem begins when I attempt to use the Class D amp, as this product will only have the single speaker (no HP out)

I am seeing proper enable of the amp, write 0x86 to P1/R32, monitor DAC flags P0/R37 D4 sets.

I have at a few points had valid audio from the speaker, so I know I am able to get the proper audio routing.

However, I am now at the point where I get nothing but over current faults being set. I can read and clear the flag P0/R44, but as soon as I reenable the amp it comes right back. This happens with open SPKP/M terminals, the prototype filtered layout (ferrite bead, pF cap to ground) and 8 ohm speaker, as well as with just the 8 ohm speaker.

I have changed speakers and DAC3100's, I get an initial blip on the scope at the speaker terminals then it faults.

Any suggestions are appreciated!

Thanks

Matt

over 9 years ago

0 Don Dapkus over 9 years ago

TI__Guru**** 189399 points

Hi, Matt,

Welcome to e2e, and I'm sorry that you're having problems with our products.

Over-current events on a class-D amplifier can be due to excess peak output current - for example, if you have some excess capacitance to ground, at the switching frequency, this can cause large current spikes that exceed the over-current threshold level.

Also, if the layout is not good, decoupling is not tight, etc, weird problems like this can arise.

I suggest you look at the EVM (here) and compare your layout and components to what we used on the EVM. You may even want to order one of these to verify that your register settings, etc, are all correct.

-d2

0 Matthew Harlan over 9 years ago in reply to Don Dapkus

Intellectual 345 points

Hi Don

Thanks for the suggestions.

I went ahead and picked up an eval board shortly after the holiday. I was able to confirm my register settings were acceptable.

I did a bit of surgery to the EVM, spliced our control lines in and held the the USB interface in reset. Resulted in good audio with enough power from the DAC to smoke our teeny speaker :)

Latest board rev has significantly more bulk capacitance on the speaker supply to the DAC320, I removed the EMI filtering on the ClassD outputs and general decoupling has been moved as close as physically possible.

I will update on the results when the next batch of boards arrive.

Thanks again for the help.
Matt