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INA849: Issues with output balancing the output using a DC servo feedback

Jan Volkering
Intellectual 530 points
Part Number: INA849
Other Parts Discussed in Thread: PGA2320, OPA192, OPA140

Hi,

I am using the INA849 in a differential microphone setup as described in the INA849 datasheet on page 24 using a gain setting of 40dB.

For a flexible gain setting of the microphone amplifier the INA849 is followed by a PGA2320 allowing a maximum gain of 40+32=76dB.

In order to keep the DC offset at the output of the PGA2320 at a minimum I incorporated a DC servo over the INA849 using an OPA140 or OPA192, feeding back the output of the INA849 via the OPA192

(setup as integrator with a 100K/1uF integration constant) and its output directly connected to the REF input.

Tina simulations showed this should work fine.

Building the design according to the Tina schematic the output of the INA849 slams to the positive or negative rail and no DC balancing is achieved as I expected from simulations.

I can send the Tina schematic if needed.

Is there a difference in behaviour (internal working) between the Tina model and the actual device that causes this behaviour or do you have suggestions why this happens?

  • 0
    TI__Guru 55466 points

    HI Jan,

    Can you please provide the complete schematic, including the OPA140 (or OPA192) DC servo and PGA2320. Please include the supply connections. 

    What is the expected amplitude voltage range from the microphone?

    Yes, please also provide the TINA simulations as well with the DC servo; this will help us debug the problem and verify the circuit.

    Thank you and Best Regards,

    Luis

  • 0
    Intellectual 530 points

    Hi Luis,

    The microphone sensitivity is around 15mV/Pa

    I sent the schematics and Tina file in reply to your email.

    Hope this helps.

  • 0 in reply to Jan Volkering
    Intellectual 530 points

    At high SPL (speaker testing) I have the gain of the PGA at 0dB, so total gain 40dB

  • 0 in reply to Jan Volkering
    TI__Guru 55466 points

    HI Jan,

    If you replied to the E2E email, please note, I will not receive the email reply with your TINA or schematic attachment.

    I have contacted you via E2E private conversation so you may share your schematic and TINA simulation files.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 530 points

    Hi Luis,

    Did you receive the schematics and Tina file?

  • 0 in reply to Jan Volkering
    TI__Guru 55466 points

    Hello Jan,

    I have not received the schematics, nor the TINA simulation file.

    I have sent you another private message today, requesting the schematic/TINA file.

    If you would like us to review the schematic and/or simulation file, please reply to this post attaching the schematic and TINA files in this public forum, by using the insert button on the menu, see image below...

    Alternatively, if you do not wish to post the files in the public forum, please reply to the private message, attaching the files in the private conversation...

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 530 points

    Hi Luis,

    Call me stupid but I am not able to upload either a .TSC nor a .pdf file.

    If I enter the path to the files on my PC I get the response: The file or URL is not allowed to be inserted.

    Any suggestions?

  • 0 in reply to Jan Volkering
    TI__Guru 55466 points

    Hello Jan,

    I just sent you an email message. We will continue the conversation via direct email.

    Thank you and Best Regards,

    Luis