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PCM1794A: The I/V converter for PCM1794A

samba wang
Prodigy 80 points
Part Number: PCM1794A
Other Parts Discussed in Thread: OPA4134, OPA1622

Could you help to explain the circuit of I/V converter on sboa273 is different on PCM1794A datasheet? The positive input pin on OP is tied to GND on datasheet ,but on this document is tied to Vbias  .

  • 0
    TI__Genius 14220 points
    Hi Samba,

    Welcome to E2E and thank you for your query. The engineer who handles this device is currently busy. He will respond to your query soon.

    Regards,
    Uttam Sahu
    Applications Engineer, Precision DACs
  • 0 in reply to Uttam Sahu
    Prodigy 80 points
    Dear Uttam ,

    Thanks for your information. We are just on beginning on researching PCM 179A. And we are also confused about the circuit on page 9 of TPA6120A datasheet. On this circuit, the power of OPA4134 is ±5V, but we calculate the output voltage as below:
    Vout=10.1mA x 1kohm=10.1V . 10.1mA is the output current of PCM 1792A and 1K resistor is RF . So Vout is higher than power . Can you help me for checking this ?

    thanks
  • 0 in reply to samba wang
    TI__Guru 52663 points
    Hi Samba,

    Can you please link me to the sboa273 document that you are referring to?

    For you second question, I think you are correct, the OPA4134 should not be powered by ±5V. The OPA4134 is specified up to 36V, so it is reasonable to connect the OPA4134 supplies pins to the same 12V supplies used by the TPA device.

    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 80 points

    Dear Paul

    Thanks for your help .

    I am really sorry that there is one typo on "sboa273" , it should be SBOA237 . And the link is " www.ti.com/.../sboa237.pdf"

    Thanks!

     

  • 0 in reply to samba wang
    TI__Guru 52663 points
    Hi Samba,

    What Wayne is describing with the Vbias is to a way to optimize the design to reduce the common mode voltage of the OPA1622, specifically so that lower supplies can be used. The PCM1794A datasheet specifies ±15V supplies. If you were to try to use ±10V or lower, you may experience clipping when the inputs violate the common mode limits. If you add a Vbias voltage to the noninverting inputs of the OPA1612s to account for the 6.2mA common mode current from the PCM, you can ensure that the outputs of the I/V stage are centered around 0V, thus bringing the common mode voltage of the differential amp to nearly 0V. With wider supplies this may not be necessary as the common mode range is much wider as well.

    Let me know if that answers your questions.

    Thanks!
  • 0 in reply to Paul_Frost
    Prodigy 80 points

    Dear Paul

    Thanks for your help. And i think it is very usful for our desing .

  • 0 in reply to samba wang
    TI__Guru 52663 points
    Great to hear. I would like to see your circuit once it done. :)