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TPA3110D2 Auto reset at higher volume

Other Parts Discussed in Thread: TPA3110D2

Hello,

I recently put together a stereo amp based around the TPA3110D2 IC. I essentially used the suggested application schematic right out of the spec sheet (fig. 37) with a few embellishments from the EVM schematic (gain control jumpers, plimit defeat jumper, ferrite beads on the supply, just some stuff to play around with.) I used my mp3 player as the audio source. The power supply is a 14.4V NiMH battery pack. The unit works, but only at a low level volume. If the volume on the mp3 player source is turned up above a third of its capacity, the TPA3110D2 amp keeps auto-resetting itself. It should be noted that the only speakers I had handy were a pair of 4 Ohm, 100W rated power speakers. Is the amp resetting due to over current as a result of my speakers? If so, what do I need to do differently? If not so, what's going on here?

Thanks!

Chad

TPA3110D2 STEREO (Schematic).pdf
  • Hi Chad,

    It looks like the Ferrite Beads (Q3, Q4, Q5, and Q6) maybe saturating at higher output power level. FB typically saturates more easily than inductors. In many beads, low frequency impedance falls by a factor of 10 or more at rated current. Make sure that the FB's impedance remain high enough to provide sufficient filtering at the peak current it will carry. Try remove the capcitors to ground (such as C18..etc) and see if the OC condition will stop.

     

    reg,

    Paul.

     

  • Paul C, you sir, are a life saver.

     

    I removed capacitors C18,19,20 & 21 and the over-current condition cleared up. Excellent. As a followup question, should I be worried about removing the caps? Should I replace them with different capacitors? What were they there for in the first place? Sorry to hound you with amateur questions like this. This is not only my first class D amplifier project but my first surface mount soldering project. (It became pretty obvious that if I wanted to dabble in class D I was going to have to go surface mount.)

    As for the ferrite beads, they seem to be doing the job. What sort of performance difference would I expect to gain by beefing up the filter system?

     

    Thanks again, you're the best.

     

    -Chad

  • Hi Chad,

    I'm glad that it worked out. The problem is caused by the ferrite beads saturating at high current level. I have attached a ppt that explains the saturation issue and FB filtering from pg 45 to pg 50. In the last few pages, there is some good info on FB - It shows how the impedance change with load current and frequency. When your FB saturates, its impedance drops and the output becomes AC short via the filtering cap. That is why the over current protection function was triggered at high output power level.

    Enjoy your first Class D project!

    reg,

    Paul.

     

    Crct-dsn-portable-audio+EMC-090112.ppt