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TPA3255: TPA3255 no output

Part Number: TPA3255

Hello,

finally our board is ready to test. But we cannot get any output from the TPA3255.

One question is: M1 and M2 should read high level on min. 1.9V input. So we decided to set them with resistors from our 3V3 source.

Same source is used to tie RESET on a high level. Same GND-Plane for everything.

This is the signal we send to Input A and B:

If I send only a signal to Input A or B than the TPA3255 starts drawing current (about 1 Amp).

As soon as I apply the symmetrical signal, the input current is about 100 mA.

Tie RESET to GND reduces this to 85 mA. 

So it looks like the chip is working somehow... but we cannot figure out what the problem is.

Did we do something wrong on the schematic?

Thank you and best regards

  • Hello Christopher,

    • Can you show your ADC output circuit going into the input pins?
    • Are you seeing this at all input levels for your differential signal or just for the waveform showed
    • What load impedance are you using
    • Can you test at a lower PVDD voltage
    • Is this behavior being triggered for both when the load is connected and disconnected?

    best regards,

    Luis

  • Found the problem... my student systematically didn´t cover the PCB with isolating gap filler and the heat sink was shortening the input signal at the AC-couple capacitors to GND. So the signal was 0V on the input pins on each of the three PCBs. I found the issue today and fixed it. Now everything is fine.

    I was wondering on how big the heat sink must be to deliver 200 W from TPA3255... a 120x70x10 mm riffled alumina block seems to be too less cooling.

    Is there a formula of the heat dissipation of the chip at given continuous power?

    Best regards

  • Hello Christopher,

    For our EVMs we use this for our heatsink: Advanced Thermal Solutions ATS-TI1OP-519-C1-R3. This can be purchased by vendors.

    While it's not for this device we have a Thermal App note for our automotive class D that will be useful to calculate the heat dissipation https://www.ti.com/lit/an/slaa996a/slaa996a.pdf

    best regards,

    Luis