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Original question:

TLV320ADC6140: TLV320ADC6140 Microphones connection

TLV320ADC6140: differential signal voltage levels when interfacing OPA1633 FDA with TLV320ADC6140

Azmat Bilal
Prodigy 40 points
Part Number: TLV320ADC6140
Other Parts Discussed in Thread: OPA1633

we are desiging an audio circuit where we use a fully differential amplifier OPA1633 as a preamp for the ADC TVL320ASC6140. the output of the FDA is adjustable and the moment we are generating a differential signal with +2.5 to -2.5V peaks and VCOM set to 0V. we would like to know the best topology to interface it to the ADC. to be more specific
1 - can we directly interface the +/- 2.5V differential signal to the INP and INM of the ADC. can the ADC input tolerate negative voltages? in the datasheet the absolute maximum ratings show -0.3 - AVDD. or should we change the VCOM of the FDA to half of AVDD i.e. 3.3/2=1.7V?
2. should there be a DC blocking capacitor between the preamp and the ADC.

  • +1
    TI__Genius 14020 points

    Hi Azmat.

    Fully-differential the device supports 2 Vrms, (2.83Vpeak) when AVDD is 3.3V; This reduces to 1Vrms when AVDD=1.8V. For your input conditions, I recommend 3.3V and the device will work fine.

    I also suggest AC coupling your input signal with 1uF cap for best performance and no need for common mode matching.

    You can DC couple the input signal as well, just adjust your common mode of your amplifier or configure MICBIAS to AVDD/2.

    So, in short, the device will be okay in AC or DC coupled configuration, just ensure AVDD=3.3V.

    Regards,