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TPA6120A2 - few questions about design

Mateusz Kaluzny17
Expert 1065 points
Other Parts Discussed in Thread: TPA6120A2, OPA1656, BUF634, LME49600

Hello, dear Ti community.

I've got some questions about TPA6120A2.

1) how about PCB design for this part? I especially ask about sensitive nodes of this HF amplifier, should I remove unwanted copper under the sensetive pins (like it was done with similiar HF parts from THS family etc.).

2) how about building composite amplifier with OPA1656 + TPA6120A2? Does it require any additional work to make it stable?
2A) how about making output impedance very low (typical TPA6120A2 design is using 10 ohm at each output which is kinda high value),
2B) how about it's power capabilities to drive 32 ohm headphones via this composite amplifier?

I'm very interested about those parts due to prices and availability, but due to TPA6120A2 specification and origin (HF amplifier) I'm curious what needs to be done to make it perfectly stable and working good.
OPA1656 also looks promising and yet cheap enough to use it widely ;)

Regards, have a nice day.

  • 0
    TI__Guru* 95145 points

    Hi Mateus,

    We'll take a look at your questions and provide a thorough answer within the next day.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators

  • 0
    TI__Guru* 95145 points

    Mateusz,

    Sorry for the delay on the response.

    Regarding the layout, what package are you using? You can follow the recommendations from the data sheet, and there is also a board design for each package:
    DWP and RGY evaluation boards.

    I assume you want to use TPA6120A2 as current buffer for OPA1656, this application could be similar to the circuit shown at the bottom of the front page of TPA6120A2 datasheet.
    In order to keep the TPA6120A2 stable you need to follow the overall recommendations:

    • Place R at the output that can be from 10 to 100 ohms
    • Do not place capacitors on the feedback loop, route feedback loop so that capacitance is as low as possible
    • Use high feedback resistance (eg. 1k), higher resistance is better for stability but affects noise.

    Hope this helps, please let us know if you have further questions.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators

  • 0 in reply to Ivan Salazar
    Expert 1065 points

    Hi Ivan.

    I'll try to describe as best as I could what I want to create.

    1) My design is build arround composite amplifier, so I'm going to include TPA6120A2 in OPA1656 feedback loop to boost up output current.
    2) I'm looking for good stability of this combination, because TPA6120A2 is HF, high-speed part anjd VFB and CFB opamps are compensated differently I'm looking forward for some suggestions and information, because there is always more than one way to make something good and as always there are some benefits due to our choice and penalties of those.
    3) my point is to "secure" low distortion in whole audio band and low output impedance (1 ohm or lower) to be perfectly sure that it will not affect any headphones that will be connected.
    4) because TPA6120A2 is powerfull IC there is always a matter of heat so I'm still thinking about package, but at this moment I'm more interested about RGY due to smaller loops, stary capacitances and smaller footprint.

    I'm not sure now about application, because I think it will not be that straight forward as it could be with BUF634(A).
    Lowering output impedance will come with it price too, so I could include R-ISO or even L-ISO (which will affect distortion) or even both in parallel (I saw those combination few times), but R-ISO will lower my output power and increase output impedance.
    So theoretically R-ISO could be included in feedback loop, then output impedance will be low, but output power still be affected.

    How about using zobel network with TPA6120A2 output to make it stable with capacitance load that will come directly from headphone cable (a matter of few hundred pF/M).

    I want a composite amplifier due to best of both world, OPA1656 will compensate output errors of TPA6120A2 so technically it's probably best I could build without making it exceptionally complicated/expensive.

    I'm looking for some help because as you could see this not that simple as it might look from typical perspective.

    BTW: due to prices and availability of TPA6120A2 it's a good IC to play with, still much cheaper than LME49600 or BUF634 and yet more powerfull.
    I picked OPA1656 because it's great IC with very high open loop gain, low noise and distortion.

  • 0 in reply to Mateusz Kaluzny17
    TI__Guru* 95145 points

    Mateus,

    Regarding the noise-stability compensations, I included some information in my last post and also data sheet has further information at section 10.2.1.2

    RC Snubber at the output would be good to keep the device from HF oscillations, you could use placeholders and use them as needed. You could consider using the RGY EVM to evaluate the compensation of using snubber with low (or not using) series output resistor, if you want to use as low output impedance as possible.

    Best regards,
    -Ivan Salazar
    Applications Engineer - Low Power Audio & Actuators