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TAS5421-Q1: DC-Offset added to Speakeroutputs

Jens Koenig
Prodigy 70 points
Part Number: TAS5421-Q1

TAS5421-Q1:

What happens, if I add a small DC Voltage like 30mV between OUTP and OUTN? Lets assume it is done with connecting a resistor between PVDD and OUTP and another one between GND and OUTN so that a drop of 30mV is at the Speaker and thus at OUTP-OUTN and centered around PVVD/2.

Let's assume, that this is established after the device is in unmuted play mode and no Errors have occured.

Does the TAS5421 indicate a fault? Like the "DC Detect"?

Another question would be: What exactly is the DC detection threshold (see chapter  7.3.6 in SLOS814C)?

  • 0
    TI__Mastermind 44955 points

    Hi Jens,

    This DC voltage can be forced on the speaker outputs on the speaker side of the LC filter.  There will be some drawbacks.  When the device is in Hi-Z the outputs will be forced to 1/2PVDD.  There are weak internal pull downs inside the TAS5421-Q1 that will pull the output pins to ground when in Hi-Z.  This is done so that the load diagnostics will not cause a pop in the speakers.  Also, this pull down is needed so the unmute function does not cause a pop in the speaker.  From our investigations, the pop can be quite loud.

    The DC Offset detection will force a shutdown at 2.9Vdc as indicated in the datasheet electrical characteristics table.  30mV should not trigger a DC offset detection.

  • 0 in reply to Gregg Scott
    Prodigy 70 points
    THX, Gregg.
    The biggest drawback is indeed, that this DC Voltage would force a current through the Coils and then to PVDD or GND through the Output-mosfets (depending on their current state).

    I fI understand it right, i could also generate a DC Offset on the OUTP and OUTN if I put a DC between IN_N and IN_P, but in 7.3.1 this is not recommended to "ensure correct ramping of the Output voltages".
    So, what happens, if after going into Play mode, I slowly ramp up an additional DC between IN_N and IN_P?
    Jens
  • 0 in reply to Jens Koenig
    TI__Mastermind 44955 points
    Hi Jens,
    If the part is already in play mode and you then slowly force some DC in the output, I do not see a problem.