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TAS5704 LOOP Filter

Atsushi Noda1
Intellectual 390 points
Other Parts Discussed in Thread: TAS5704

When evaluating a prototype board, capacitor in LOOP Filter was damaged by short mode.(C1 47nF recomended in datasheet)
I checked OUT_X waveform,it was duty50%.(I2S signal is input)

-Is this movement right behavior?
-Could you tell me the mechanism of this behavior?

Best regards,

Noda

  • 0
    TI__Guru 57800 points

    Hi Noda,

    TAS5704 is a quite old part, we highly recommend to switch to our newer closed loop devices like TAS5760x, this device has better performance and support. About the behavior you mention it is related to the amplifiers protection system, when detecting an error the outputs will be placed in high impedance state (PWM at 50% duty cycle) until the error is removed. 

    Best Regards,

      -Diego Meléndez López
       Audio Applications Engineer

  • 0 in reply to Diego Melendez
    Intellectual 390 points


    Thank you for reply.

    Please tell me a little more.
    What kind of state does the protection circuit work?

    Best regards,

    Noda

  • 0 in reply to Atsushi Noda1
    TI__Guru**** 189399 points
    Hi, Noda-san,

    If there are clock errors, the device goes into a "limp mode" which is 50% duty cycle. So, this seems like very normal behavior given the issue with the LOOP components.

    -d2
  • 0 in reply to Don Dapkus
    TI__Guru**** 189399 points
    Hi, Noda-san,

    I think there are still some questions about this?

    Allow me to expand on my previous answer.

    The external crystal is used to drive an internal PLL. If there is a problem with the crystal, then the PLL won't be able to lock to its desired frequency. In this case, the device enters what we call "limp mode" where a crude clock is used to keep the part running. Since we don't have an accurate frequency, and can't convert the incoming I2S signals, the outputs are muted, which means they transition to a 50/50 duty cycle.

    Let me know if you need further details.

    -d2