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Original question:

TAS5805M: Audio output stops after few seconds and Fault triggered

TAS5805M: How TAS5805M Detect OCP

C%20K%20Ong
Expert 1240 points

Part Number: TAS5805M

We have TAS5805M designed with PBTL configuration for subwoofer operation.

The TAS5805M has PVDD=22V, output using L = 10uH and C=1uF, BD mode, Fsw = 768KHz, BW = 80KHz, LPF -3dB cutoff = 75Hz, output limit to <35W.

We noticed that when we sweep a 0dB 50~100Hz signal, at 75Hz, the TAS5805M will cutoff  the output and issue OCP error.

The speaker impedance is about 31ohm at 75Hz, with a phase shift from -53deg to 53deg.

After we adjust AGL, we are able to suppress the OCP.

We managed to measure that with 75Hz at maximum output, the peak current is about 1A. This is way below the 5A OCP limit.

How can OCP be triggered?

We also noticed that adjusting AGL threshold is able to prevent the OCP and lower the peak current (measured at PVDD) at the same time.

Is OCP actually triggered by the suge current due to internal MOSFET switching?

  • 0
    TI__Guru 57530 points

    Hi 

        The OC protection means to protect the MOSFET inside of our device. Our device will also test the current flow through the MOSFET. In your test, maybe you test the output current, which is already filtered.

        The picture at the end, is it the impedance curve of the speaker? I don't see the unit at the left side, not so sure. Does the impedance have large change among different frequency?  If so, this is maybe the cause of the surge current.

        Anyway, use AGL to restrain the output is a good idea. No only to solve the OC problem, also will remove the noise caused by surge current when you play the music.

  • 0 in reply to Shadow He
    Expert 1240 points

    Dear Shadow,

    1. Yes, the 1A measurement is after the fiter.

    2. Am I correct to say that 5A peak current in the datasheet actually refer to surge/peakcurrent into the PVDD?

    3. The curves are the impedance of the subwoofer box (hence you see two impedance peaks) and phase angle (the smaller amplitude curve). The unit of left side is ohm.

    4. The curve with two peaks is the impedance curve. It only has hugh change for frequencies around the two peaks.

    Best Regards,

    CK

  • 0 in reply to C%20K%20Ong
    TI__Guru 57530 points

    Hi CK

       The energy indeed comes from PVDD. But I'm sure you will also put capacitors at the PVDD side, so the surge current will be provided by these PVDD capacitor, also hard to test it,

       As the impedance has such changes, use AGL to have some restrain would be good.