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Original question:

PGA300: PGA300 MAX Voltage of FB-

PGA300: Negative Feedback voltage

Angel Martinez
Prodigy 10 points
Part Number: PGA300

Hi,
We configured voltage mode output 0-10V and It works fine for a while. About 3 hours later the chip increase their temperateure and then broke the chip.

The maximum voltage on FB- is 3.6V but Output Voltage is up to 10V. The value of resistor is 110H.

Can you help me to resolve this issue?

Thank you

  • 0
    TI__Guru** 113765 points

    Hi Angel,

    Welcome to the E2E forum!  Are you using the EVM?  And if so, have you verified that the configuration is as shown in the user's guide?

    To be totally transparent, I have only supported this device for a short time and I'm still learning it.  Unfortunately I will not be able to go to the lab for any verification until the end of next week.  If you change the gain of the DAC output to say 4V/V, the output voltage will lower.  Can you verify if the PGA300 works well in that voltage range?

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 10 points

    HI Bob,
    Thank you for your reply.
    I'm using this configuration. I don't understand why the -fb maximum voltage is 3.6V but we can configure 10V output and the EVM schematic connect this out PIN (10V) to -FB. 

    I checked with output 0-2V and it works fine. 

    Thank you

  • 0 in reply to Angel Martinez
    TI__Guru** 113765 points

    Hi Angel,

    Thanks for the information update.  I will need to review this in the lab to understand better.  As I said previously I will not be able to go to the lab again until the end of next week.  Let me know if you find anything else that you see.

    Best regards,

    Bob B

  • 0
    Prodigy 10 points

    Hi Bob,

    how was your tests?

    thank you

  • 0 in reply to Angel Martinez
    TI__Guru** 113765 points

    Hi Angel,

    I was in the lab most of the day on Friday, but was not able to get to look into this issue yet.  Hopefully I will have time to do so today.  In any case I will let you know later today where I'm at.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hi Angel,

    I believe the datasheet has an error regarding the FB- maximum input voltage.  As the DAC output can follow the Vpwr supply, and the FB- can be connected to VOUT, the FB- pin should have a maximum of Vpwr + 0.3V.

    Now with that said, there may be a compensation issue where the output may not be stable depending on the cap loading.  Please review the information in this application note regarding the DAC amplifier stability with capacitive loads.  The EVM is designed for a 5V output driving a maximum load of 100nF.  It is possible that the output of the DAC becomes unstable at larger voltage outputs.  Do you have anything connected to VOUT?  If so, can you identify the load capacitance?

    If you feel like you are still having issues, please send me a picture of your EVM so that I can identify all the jumper settings.  It would also be helpful to know the GUI configuration settings.

    Best regards,

    Bob B

  • +1 in reply to Bob Benjamin
    Prodigy 10 points

    Hi Bob,

    Thank you for your time. We don't connect anything on Vout. Only a Multimeter measuring the Voltage on Output.

    There are differences between datasheet schematic  and  EVM schematic about Voltage configure and feedback resistor.

    Thank you