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TPA3221: Small foot print output filter for TPA3221

Markus Friberg
Prodigy 150 points
Part Number: TPA3221
Other Parts Discussed in Thread: TPA3245, LM5010

Hi,

I'm designing an audio power amplifier using TPA3221.  have pretty limited space for my board so I'm looking at minimizing the footprint for the output filter.

The inductor 10uH) and cap (1uF) that are used on the EVM-board are bigger than I can fit!

I wonder if it is possible to use alternative more compact inductors and capacitors!

I have been looking at this inductor:

ETQP4M100KVC from Panasonic

ETQP4M100KVC (output filter inductance 10uH).pdf

Regarding the caps I have not found any yet! Could someone recommend me a smaller cap that could work well! Smaller than the one on the TPA3221-EVM!

Best regards

Markus

  • 0
    TI__Guru 61380 points
    Markus,

    I briefly looked at the datasheet of the inductor and didn't find the important Inductance vs. Current curve, do you have this?

    We care about this curve because it's shape dominates the THD performance and our device is limited only by the inductor at higher output power.

    It's hard to know exactly how an inductor will effect the THD curve and idle current so we typically try this in our lab. I would suggest mounting a desired inductor on the EVM and testing it for yourself to see if it suits your needs. Keep in mind that there is a minimum inductance listed in the datasheet and that inductors typically reduce in inductance as you drive more current through them. If the inductor value dips too low at higher output current, the TPA3221 IC might be damaged.

    For the capacitor, we care mostly about the voltage ripple stability since the cap is the shunt element in the LC filter. We have found that we need a film cap to feel safe that the ripple voltage of the PWM won't kill the cap. This is why the cap voltage on our EVMs are oversized compared to the voltage swing of our output.

    We know that smaller caps could work but we haven't concluded on any models yet unfortunately.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 150 points

    Hi Adam,

    Thanks for your reply! I found the inductance-vs-current curve. It Changes about 20% from 0A to 6A. See attached plot!

    Best regards

    Markus

  • 0 in reply to Adam Sidelsky
    Prodigy 150 points
    Hi,
    I found one from Coilcraft as well: www.coilcraft.com/.../ha4158.pdf

    I will Power my TPA3221 with 24VDC and have minimum 4ohm speakers and load each channel with maximum 50W!

    Best regards
    Markus
  • 0 in reply to Markus Friberg
    Prodigy 150 points

    UA8014.pdfECWFE2W105 (filtercap 1u 450V).pdfHi again,

    I have now decided which inductor and cap I will try! See attached!

    Best regards
    Markus

  • 0 in reply to Markus Friberg
    TI__Guru 61380 points
    Markus,

    Good choices. As you probably saw, we use that same inductor on our TPA3245 and 3244 EVMs. As for the capacitor, the one you chose is very similar in size to the PHE426 but it's shorter. Since the heatsink dominates the height of the EVM we didn't go any shorter on the cap.

    Regards,

    -Adam
  • 0 in reply to Adam Sidelsky
    Prodigy 150 points
    Thanks Adam,

    I wonder if there are any specific guidelines or recommendations for EMI-filter on the DC-power-supply-input for a design using TPA3221!

    In my design I will use 2x TPA3221 and when I look at the EVM schematic there are only 3 caps on the DC-supply inputs! Is this sufficient from an EMC(EMI) point of view? I am thinking of HF noise conducted out on the DC-supply-cable and then causing RF-emissions!

    I will supply my design from an AC/DC adaptor with about 1.5m DC-cable.

    Do I need to add for example a common mode choke at the DC-supply-input to my board?

    Best regards

    Markus
  • 0 in reply to Markus Friberg
    TI__Guru 61380 points
    Markus,

    I heard back from the power team.

    What voltage is your AC/DC adapter? if it is between 12V and 15V then you can bypass the LM5010 switching converter and save it's EMi effects. That's the only source on the board that we figure would add EMI. If the AC/DC adapter is clean then you should be okay, if it's not, you may add a common mode bead to prevent the 1.5 meter cable from radiating.

    Is this just for the EVM or are you making a product?

    Regards,

    -Adam