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TPA3116D2: Power limit in TPA3116

Wiky Liao
Intellectual 1940 points
Part Number: TPA3116D2
Other Parts Discussed in Thread: TPA3128D2,

Page 16 in TPA3116 datasheet, the table 3 shows the power limit example. I have three questions about that:

1. how to understand: Vp = 4 x PLIMIT voltage if PLIMIT < 4 x Vp ?

2. I think that PLIMIT voltage = GVDD*(R to GND)/ (R to GND + R to GVDD), is that correct? if this is right, when PVcc = 24V, PLIMIT= GVDD, I think the R to GND is Open, and R to GVDD is short, but the table shows the opposite, why?

3. Can you give me the formula of calculating the output voltage? I can't understand how it works. Thanks!

  • 0
    TI__Mastermind 25895 points
    Hi Wiky,

    Shawn can help you out with these questions. Please check back for a reply from him shortly.

    Best,

    Alex
  • 0
    TI__Mastermind 24835 points
    Hi Wiky,
    The PLIMIT circuit sets a limit on the output peak-to-peak voltage. The limiting is done by limiting the duty cycle to a fixed maximum value. The limit can be thought of as a "virtual" voltage rail which is lower than the supply connected to PVCC. The "virtual" rail is approximately four times the voltage at the PLIMIT pin. So, Vp=4*PLIMIT voltage if PLIMIT is less than 1/4*PVCC. And your understanding for GVDD and PLIMIT is correct. "GND" and "PVCC" are swapped in the table. They are typos, and we will revise TPA3116D2 datasheet. Before this, you can refer to TPA3128D2 datasheet for PLIMIT fucntion description. PLIMIT feature is the same for these two devices. Sorry for the inconvenience.
    Best regards,
    Shawn Zheng
  • 0 in reply to Shawn Zheng
    TI__Intellectual 1940 points

    Hi Shawn,

    Thanks for your reply in detail. I have got your points.

    How about the output voltage? I can't calculate the exact value from plimit voltage or PVCC, can you give me an example of calculation? Formula is much better. 

    Wiky Liao

  • 0 in reply to Wiky Liao
    TI__Mastermind 24835 points

    Hi Wiky,

    The data in this table is based on the bench measurement instead of calculation, but it should be close to the calculation result. The following picture shows how PLIMIT works.

    The formula Vp=4*PLIMIT is a rough calculation, but not quite accurate, because this feature is just used to limit the output power to protect the speakers. Please note the output voltage in this table is RMS value.

    Let's take the first row in the table as an example. Input is 1Vrms and gain is 26dB, so the output is 20Vrms. But Plimit voltage=GVDD=6.9V, then Vp is around 27.6V, but PVCC is only 24V, then PLIMIT actually takes no effect. Because the output is clipped by power supply before PLIMIT. The peak value of the output signal is close to 24V, and where the output is clipped to 24V if it's larger than 24V. The measured the output is 17.9Vrms.

    For the thirdrow, the PLIMIT voltage is around 6.9/(24+51)*24=3.23V. And 4*3.23=12.92<24V, so PLIMIT take an effect in this case and the maximum output is 12.9V.  In this case, the output is clipped badly and is very similar to a square waveform, so the measured output RMS value is very close to the peak value.

    Best regards,

    Shawn Zheng 

  • 0 in reply to Shawn Zheng
    TI__Intellectual 1940 points
    Hi Shawn,

    Got it, thanks for your reply. I understand.

    Best Regards.
    Wiky