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TAS5421-Q1: Maximum Overcurrent with short circuit

Jens Koenig
Prodigy 70 points
Part Number: TAS5421-Q1

What is the Maximum current if an Output (OUTP or OUTN) is suddenly connected to the Battery? Can it go above 4A (mentioned in 6.1 of SLOS814D), even for a very short time?

And how fast is the Overcurrent Shutdown?

THX

Jens

  • 0
    TI__Mastermind 34305 points

    Jens,

    What is the voltage on the Pvvd pin on the device?  If is is lower than the battery voltage and you short the output to battery there is no protection for this.  The inrush current can occur even if the device is in standby mode.  

  • 0 in reply to Gregg Scott
    Prodigy 70 points

    Amplifier is in PLAY mode. And of course there are coils (22uH) between Outputs and Speaker.

    Case1:

    Voltage on the Pvvd pin on the device: 12V

    Voltage,on one Speaker terminal is accidentally tied to: 16V

    Then a current is going through internal Diode from OUTP to PVDD. That is perfectly clear. The current through this Diode might flow forever but might be limited by external circuitry. But:

    -> The MOSFET between OUTP and GND will most probably drive a high current for a short time and overcurrent detection will kick in. Is that right?

    Case 2:

    Voltage on the PVDD pin on the device: 12V

    Voltage one Speaker terminal is accidentally tied to: PVDD

    The Diode of the upper MOSFET is not conducting.

    -> The MOSFET between OUTP and GND will most probably drive a high current for a short time and overcurrent detection will kick in (calculation below). Is that right?

    Calculation: Let's say, we have all Rs in the chain to sum up to 0,75Ohm (Rmosfet, Rcoil, Rconnectors etc.), then the theoretical max current is 16 Amp. Let's assume, the current through the coil was approx 0 before the short. Then, after 3 PWM cycles with OUTP ~100% (a worstcase) to GND, we would get something like 3,5 Amps. Does the Amp now detect the overcurrent or is there a longer time, where the current through the coil could build up even more?

  • 0 in reply to Jens Koenig
    TI__Mastermind 34305 points

    Jens,

    Case 1 will not always work.  This assumes the device is active.  The body diode of the High-side FET will still conduct when the device is in Standby mode.  In standby mode the device is not active.

    Case 2.is what we consider a normal short to battery condition.  The body diode of the high-side FET cannot conduct and there will be a overcurrent event and shutdown the device less than one cycle of the PWM.  If the device is inactive and the output is in H-Z mode, nothing will happen.

  • 0 in reply to Gregg Scott
    Prodigy 70 points

    Thanks, Gregg.

    In my both examples the short is attached during Play Mode. That the Diode is still conducting is another Problem, right.

    The important thing for me was, that the shutdown is that fast.

  • 0 in reply to Jens Koenig
    TI__Mastermind 34305 points
    Jens,
    In case 1, even after a protection event the short is still present and the High-Side FET body diode will still conduct.