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TLV4021: need a device to sense voltage on an audio path and communicate to MCU

Part Number: TLV4021
Other Parts Discussed in Thread: TLV9062, TLC555, TLV7011

I need to find a way to wake-up my system by simply sensing the analog audio

input (analog mode only). So, do you have any Audio detector with around 1mV RMS threshold?

•             fast attack time (ms)

•             low release time (30-40s)


I saw some Low Cost, Low Power, True RMS-to-DC Converter like the AD8436 but there is no attack/release time.


Would you please help with a solution on how to sense an analog voltage on a bus and communicate voltage present to the MCU. 


Thank you, 


  • Adam
    I am not familiar with the audio terms "fast attack" and "slow release time". The tlv4021 is a comparator with an integrated reference. were you thinking it is possible to apply our comparator to that application? you mention 1mV rms, so the only thing I could imagine offering is to ac-couple the audio line, gain it up with a low noise amplifier, and detectect when the output crosses our 200mV internal threshold. this technique is common for current sensing where current levels are detected across a shunt resistor. Other than a suggestion such as that, I am not sure how to assist. we can discuss offline but I wanted to make sure that I was understanding your question correctly.
  • Hi Chuck,

    the fast attack means, that the enable needs to happen with in ms and the low release time means that the enable needs to remain high for 30-40s after no more audio signals were detected and then go low again.
    -> enable needs to go high with in ms after detection and go low again after 30s with out detecting any signal

    Did this clarify the question?

    BR, Nico
  • Hi Nico,

    Yes this helps clarify the question.

    Since audio signals are bipolar, would it be ok to look for only the negative portion of the audio signal for your application?

    Our idea was to AC couple the audio and gain it up, and use peak detect to hold the enable for a long period of time, and feed this signal into a comparator to communicate the signal to an MCU.

  • Hi Jonny,

    Thank you for the fast answer. Do you have a reference design available for a peak detector with a long enable release time (at least 30s)?

    Best regards,
  • Hi Adam,

    I would do it this way:

    And with separated "scope" traces:



  • Nico,

    Sorry for this late response, but I am currently running simulations to try and achieve a long enable release time of 30s. I will try to provide another update later this week.

    Thanks for your patience!

  • Hi Jonny, hi Kai,

    Thank you for your suggestions. They where very helpful.

  • Hi Nicolas,

    I should say something about the circuit:

    OPAmp TLV9062 (U1) provides a very high gain, limits the bandwidth of input signal and references it to mid-supply. To provide a fast attack time C4 is only 22n. Comparator TLV7011 (U3) forms a proper trigger signal for the monoflop TLC555 (U2) which is wired as "retriggerable" monoflop by the help of D2. D2 is very simple but effective.

    V1 should be a bit filtered to make the circuit more immune to supply voltage noise. This isn't shown in the above circuit. But you can easily add a RC low pass filter of let's say 1k and 22µ between V1 and R1.


  • Hi Kai,

    Thank you for the background. I will consider your proposition.