• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 31 subscribers
  • Views 216 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPA3118D2: DC detect protection

Zeng.
Prodigy 90 points
Part Number: TPA3118D2

Tool/software:

Hello

In our application we planned to use TPA3118D2, but just now noticed that it has a DC protection feature disabling the IC at very low AC frequencies. While such feature is beneficial in audio applications, in our case we have sub-Hz signals that have to be amplified. We also use DC coupled inputs to overcome high pass rejection. 

I have a few questions 

1. Is there a way to somehow disable this feature or some other workaround to make it work at 0.5Hz or even slightly below it?

2. Are there other ICs with similar spec but without this feature?

3. Does this feature uses output signal voltage or input  signal voltage to disable output when the signal is above some threshold for  too long ?

  • 0
    TI__Guru** 108685 points

    Hi Zeng,

    We'll look at your questios and come back with further information soon.

    Best regards,
    -Ivan Salazar
    Applications Engineer

  • 0
    TI__Mastermind 20101 points

    hi, zeng

    1.this is an analog device, it cannot be disabled.

    2.i checked some similar AIN amps, they seem all have this feature.

    3.how low does your input signal it is, if it is less than 2hz, then there might no way to solve it. if it is above 2hz, i check below section in the DS, it might somehow help you.

    thanks

    jesse

  • 0 in reply to Jesse Ji
    Prodigy 90 points

    Hello Jesse and Ivan

    Thanks for the prompt response.

    I'm not sure how pulling SD pin low would help in my case - wouldn't it basically disable the amplifier?

    I also have a question about how this feature is implemented. According to the table that Jesse attached, this mechanism is triggered by the output offset voltage, but the IC has access only to the switching node (unfiltered output).

    Any chance that what triggers the protection is actually input offset voltage? If yes, then would introducing a short negative pulse (basically bringing input to 0 for a few dozens/hundreds of ns) help to "cheat" it?

    Thanks

  • 0 in reply to Zeng.
    TI__Mastermind 20101 points

    hi

    the trigger is base on the dc offset happen at output.

    if the differential input originally exist small dc bias, which be amplified at the output. this can lead to dc detect be triggered.

    it is not detect the signal at the speaker. it detect the output before LC filter. if the duty cycle is too large which might trigger the dc fault.

    thanks

    jesse

  • 0 in reply to Jesse Ji
    Prodigy 90 points

    Hi

    Could you please explain how too large duty cycle can cause DC detection? I mean that duty cycle can be large also when the signal is at 1kHz and there will be no DC detection. 

    Could you also please respond to my question about "cheating" the mechanism from the previous time?

    Thanks

  • 0 in reply to Zeng.
    TI__Mastermind 20101 points

    hi Zeng

    low frequency signal naturally has one side large duty cycle, also because the frequency is low, the duty cycle sustain time is also longer, also low frequency signal is also get more close to DC voltage. which make the trigger easy to happen.

    "cheating" mechanism might work. i just know some customer using this kind of method for reducing pop noise.

    but as i said before, tpa31xx is for processing audio signal which mean 20hz-20khz is what it be designed for.

    out of this range, TI cannot ensure its behavior.

    thanks

    jesse