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TPA3251: Current limit on custom DC/DC boost converter.

Anton Grivans
Prodigy 160 points
Part Number: TPA3251
Other Parts Discussed in Thread: TPS43061, PCM1690, TIDA-00874

Hi,

I'm currently working on a DC/DC boost power supply for the TPA3251 36V supply and have a couple of questions.

1. I wanted to use a DAC (PCM1690) to be able to connect a DSP to it. And this particular DAC has 8V peak-to-peak differential output. Does it mean that the amp will see 2V peak at each input? Or will the amp treat it like a 4V peak signal i.e 40V output (due to the gain of the amp being 20dB)?

2. How do i calculate the current limit of the DC/DC boost converter to feed enough current into the amp? Do I use the RMS output values or Peak output values? If I have it set up to output 2x50W RMS, do I limit the current output to 110W (2X50W RMS + 10% due to efficiency), or do I make it 220W (for peak value +10% due to efficiency), considering reservoir output capacity of >1000uF?

3. How to tell how much total power can a DC/DC boost IC handle (for example a TPS43061)? I've used the Web-bench designer, but i want to be able to understand it by myself, since I might use an Analog Technologies part, due to the single IC multi-phase capability, and they don't have a similar tool.

Sorry for the long questions, I will appreciate any answer.

Thank you.

  • 0
    TI__Mastermind 27990 points
    Hi Anton,

    1. The amplifier will see the differential, but the TPA3251 has a max PVDD of 36V, and will not be able to take the full output range of the DAC without clipping.

    2. I would go for the 220W to be safe to handle peaks, but this is largely depending on how you limit your signal chain.

    3. Total power is a combination of electrical capacity and thermal capacity. You must take you efficiency into account, and this is usually covered in an app not or the data sheet of the device. For further discussion I would recommend asking on the DC/DC E2E page.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 160 points
    Hi, thanks for the answers.

    Last question, about what you said in the 1st answer. The PCM1690 has a 8V peak-to-peak differential output. The recommended DAC for the TPA3251 (as listed in the datasheet and used in TI made design TIDA-00874) has a 4.2V RMS differential output, which translates into approx. 11.88V peak-to-peak differential output (4.2V x 1.414 x 2 to get peak-to-peak diff. value). So if I understood everything correctly, with the PCM1690 connected directly to the amp I will be able to get 50W peak without any additional amplification. Is that right?
  • 0 in reply to Anton Grivans
    TI__Mastermind 27990 points
    Hi Anton,

    How much power you will get out will depend on the impedance of the load you are using. 20dB gain will be 10V/V of gain from the input to the output. Take the load impedance you plan to use and you can calculate how much power you will be able to get.

    Justin