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TPA3255: TPA3255 protection

xueli fu
Prodigy 40 points
Part Number: TPA3255
    

We are using this TPA3255 designed power amplifier in PBTL mode, we referring to the 28-page (10.2.4) chapter of the manual tpa3255.pdf, Figure 31, and reference design slar129a.pdf both provide from ti.
Question: When we connect the amplifier with an external 4Ω, 400W load speaker, it will be protected when adjusting the input signal source. Is protected every time. We adjust the volume to divide the volume into
32 levels. From 0-28 levels, the amplifier can work normally. In rare cases, it will be protected, but when we adjust to 29-32, the chip will be protected immediately. At this time, we can see that the / FAULT pin is pulled low via the oscilloscope.
But the / CLIP_OTW pin is still high.
Power supply: GVDD power supply is 12v, PVDD has been tried from 24v-48v, it is the same situation.

  • 0
    TI__Mastermind 19080 points

    Hi Xueli,

    Could you to post your schematic here? And the inductor you are using? Do you have a heatsink?

    From your description as Fault#=L, CLIP_OTW#=H, I'm suspecting you are seeing an overcurrent issue.

    TPA3255 has a gain of 21.5dB, what's the input level when the issue happened? I know you have divided into 32 volumes, but I'm interested in the input amplitude.

    BTW, the relationship between PVDD and max Pout before clipping is, Pout max = PVDD^2/2/R, so with 24V, the Pout max without clipping is 72W. You can't get high power with low PVDD supply volt.

    Regards,

    Hao

  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 40 points

    Hi hao,

    This is my schematic here.I have a heatsink.The inductor is ma5127 ,10uH. the input amplitude is 3.9v+-0.5v.

    pa48vboard_v101.pdf

  • 0 in reply to xueli fu
    TI__Mastermind 19080 points

    Hi,

    First of all, in PBTL configuration, INPUTC and INPUTD should be connected to GND directly.

    Second, you are actually building a positive feedback with the Opamps on the input side. Is it your desired design?

    Regards,

    Hao

  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 40 points

    Hi,

    Sorroy ,The schematic is wrong.I check it, actually we build a negetive feedback.there is no poroblem with the feedback. 

    I connect the INPUTC and INPUTD TO GND .I works OK. But protected when it continues to work for 10 minutes.I think 

    mabye the problem is a thermal issue。

  • 0 in reply to xueli fu
    TI__Mastermind 19080 points

    Hi,

    Yes, looks like a thermal issue. You may use heatsink with higher power dissipating capability, or we say lower thermal resistance. Silicon grease is also important.

    Another point could be, use lower switching frequency to improve the efficiency and decreasing the power loss.

    Regards,

    Hao

  • 0 in reply to Sam(MPAA) Zhang
    Prodigy 40 points

    Hi,

    How can I get lower switching frequency?change theresistance from 30k Ω to 10kΩ？

  • 0 in reply to xueli fu
    TI__Mastermind 19080 points

    Hi,

    With a 30k resistor, the Fsw is set to 450kHz. Please keep this value. Another point is, what's the max output power you need? Maintain a PVDD only necessary to generate enough output power can also help to improve the efficiency. 

    Regards,

    Hao