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TPA3116D2-Q1 with very low impedance

Tom Viehrig
Prodigy 50 points
Other Parts Discussed in Thread: TPA3116D2-Q1, TPA3118D2, TPA3130D2, TPA3116D2

Hello,


I have a application and need a amplifier :)

These are the specifications:

Frequency-range: 5Hz - 10kHz
P_out: 5W
max Voltage: 2.5V max. Current: 2,5A

The impedance of the load is between 0.4Ohm and 1.8Ohm within the specified frequency range. The max. Voltage will not occur with the lowest impedance, so that the specified max. current will not be exceeded.

Is it possible to use the TPA3116D2-Q1 for this load?

I mean is the limit for the min. impedance limited by the max. current? If this is the case, I would limit the max input to 0.3V with 20dB gain to limit the output.

In the data sheet it is specified to power 100W with 2Ohm what would mean a current of 7A [=SQRT(P_out/R_load)]  which is far over the current that I need. Or am I wrong in my way looking at this? So I would think the TPA3116 could handle this low impedance if the output is limited by the input.

Or do you have a better recommendation for this application.

If I forgot any information please ask, I'm new in this field of application :)

Kind regards Tom

  • 0
    TI__Expert 5000 points

    Hi, Tom

    What is value of your PVCC? TPA3116 support 4.5V~26V operating voltage. If the Load's DC resistance is 0.4ohm,  Pout=4.5^2/(0.4*2)=25.3w.

  • 0 in reply to Peter Cao
    Prodigy 50 points

    Hello Peter,


    The PVCC will be 12V.

    Pout = 12V^2 / (2*0.4Ω) = 180Watt

    In the data sheet the max. output for mono is 100W, so 12V would be too much for my application if I would like to use the full range.

    Do I see this right that this for the output of a 12V peak sine signal or let me say for the max. input signal?

    Am I right if I say that the max. PVCC would be: sqrt( 100W * (2*0.4Ω) ) = 8.9V if i want to use the full range?

    But what if I want a sine signal as output with voltages only between 0.5V and 2V (depending on the frequency (5Hz to 10kHz)). 

    For example if i take the max. 2V with the 0.4Ω my Pout would be only 5W. So could I use PVCC 12V if I control the output via the input signal in that way that I will only get this low voltage as output (with a 20db gain this would mean a max input of 200mV)? Or am I wrong in thinking that way?

    Kind regards Tom

  • 0 in reply to Tom Viehrig
    TI__Expert 5000 points

    Hi, Tom

                  What is the minimum load Class D can support? There are several reasons:

    •  The over current protection point. For example, in PBTL mode, TPA3116D2 support 1.6ohm, this device's max Supply voltage is 26V, which means the max output current will be 26/1.6=16.25A. OCP (over current protection) threshold will little larger than this value, if trigger the OCP, the device will shutdown to protect device.With BTL, the OCP current will be a little higher than 8.1A. For example, TPA3130D2 has a different Over current trip point with TPA3118D2 and TPA3116D2.

    • Thermal dissipation capability of your system.  Large current will cause large power consumption on RDSon, if you play a continuous sine wave a long time with large current, the device's die temperature will increase. So the OT protection also limit the Max output power. 

      For example, TPA3118D2 is a pad down version and TPA3116D2 is a pad up version (with heat sink), since the over current trip point is the same, but the output power are different.

    • Same output power, smaller load will cause higher power consumption on RDSon, because the current flow through the RDSon will increase.

        For example, PVCC=12V case.    8ohm load: efficiency=95% with @Pout=20w;  4ohm load: efficiency=90% with @Pout=20w;

     

    For TPA3116D2 (with the Heat sink which you can find in EVM user guide), with PBTL, the device's power consumption (acceptable) is 10W without OT. You can find in below curve.

        

  • 0 in reply to Peter Cao
    Prodigy 50 points
    Thank you for your answer Peter :)

    I think I can stick to the limiting values for my application. I'll give it a try with an Evaluationboard.