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Original question:

OPA1622: PCM512 + OPA1622 + BUF634

OPA1622: BUF634

Jahongir Dodokhonov
Prodigy 130 points
Part Number: OPA1622
Other Parts Discussed in Thread: BUF634, PCM5102

Hi there !

Sorry for bringing up the related thread again, since I missed some points I would like to ask last time.

The question is with regards to the schematic provided in the related thread. 

In the datasheet for BUF634 a noninverting pin of the OPAMP is tied to ground with a 100K resistor. Is there a need for this resistor in this schematic?

Regards,

 

  • 0
    TI__Genius 12815 points

    Hello,

    The reason for the 100k resistor is to DC bias the devices common mode voltage to mid supply through high impedance. This resistor is necessary if the signal source is ac coupled with the capacitor shown on the input in the product datasheet. The capacitor is DC blocking and without that resistor tied to ground there would be no DC bias for common mode voltage. 

  • 0
    Prodigy 130 points

    Thanks for replying to this thread. The reason why I created the thread is that, I implemented the above schematic with PCM5102 DAC and BUF634 and the only problem I have now is I measure a high amount of DC voltage (DC offset) at the BUF634 outputs. 

    The only thing different from the above schematic is I placed a volume know in between the DAC outputs and the composite amplifier. When the volume level is set in the middle, the DC voltage is about 15-30 mV and when it's set to its maximum it's measured about 0 mV. 

    Is there a way to eliminate the DC voltage? I don't want to place a capacitor as in BUF634 datasheet.

    Regard, 

  • +1 in reply to Jahongir Dodokhonov
    TI__Genius 12815 points

    Hello,

    The only way to eliminate the DC voltage is to use a DC blocking capacitor.