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TLV320ADC3101: Valid analog input voltage to AVSS

burton hui
Prodigy 40 points
Part Number: TLV320ADC3101

Per TLV320ADC3101 document,  analog input voltage to AVSS shall be  -0.3V ~ AVDD+0.3V

But from another case https://e2e.ti.com/support/audio/f/audio-forum/996671/tlv320adc3101-dc-voltage-measurement?tisearch=e2e-sitesearch&keymatch=tlv320adc3101%20DC#,

valid analog input voltage is 0.35V ~ 2.35V.   How to understand this ? Can TLV320ADC3101  measure analog input voltage >2.35V or <0.35V ?

Probably can we use  Analog PGA ( Page 1 / Register 59: Left Analog PGA Settings ) to adjust the input signal ? If yes, could you tell me the computational formula?

I did some test. The input DC voltage is 1277mv.

With 0dB gain, adc outputs 1277mv.

With 10dB gain, adc outputs 1120mv.

with 20dB gain, adc outputs 648mv

I am sorry I don't know the right formula for the actual test results

Thanks,

Burton

  • 0
    TI__Mastermind 18900 points

    Hello Burton,

    Thanks for posting on the Audio forum! Let me get back to you tomorrow.

    Thanks,

    -Cole

  • +1
    TI__Mastermind 23050 points

    Hi Burton,

    The output here is I2S, which is 2's complement referred to the full scale input range of 0.707Vrms. Thus a 0.353Vrms signal would read -6dBFS at the output and if you applied 6dB of PGA gain you would see a 0dBFS signal for the same input. 

    The input limitations of -0.3V to AVDD+0.3V are the abs max limits, not the operating range of the device. The device can measure up to 0.707Vrms centered around 1.35V, which is ~0.35V to 2.35V. 0.35Vdc input will produce a max negative code of 0x80000000 and similarly a 2.35Vdc will produce a max positive output code of 7FFFFFFF, of course keeping in mind there will be some gain error and offset associated with this since the devices are not trimmed for dc precision. If you're trying to calculate the applied input voltage you would want to convert this 2's complement  output to a decimal representation and then you could calculate the input voltage as (CODE/2^31)/PGAGain + 1.35V.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    Prodigy 40 points

    Thank you for your detailed answer. This resolved my question