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PGA305: PGA305

Lori Ferger52
Intellectual 495 points
Part Number: PGA305
Other Parts Discussed in Thread: USB2ANY

We are using the PGA305 in a current output circuit used in a pressure transducer.  We are communicating with the PGA305 using the OWI with the PGA305 GUI downloaded from the TI website. 

When the DAC counts are set to any value above 8E6,  the output of the DAC goes to 0 volts.  Also,  when using the "ADC & DAC calibration"  or the "DAC settings" page of the GUI,  the OWI and TEST_MUX_DAC_EN buttons must both be pressed again before sending another DAC value for it to work.

We have used the PGA305-EVM board previously with the on board PGA305 and circuitry and did not see this issue.  

Can you please help?

 

  • 0
    TI__Mastermind 31655 points

    Hello Lori,

    Are you communicating from the EVM to your own board with the PGA305? Sometimes protection schemes on a standalone application board can interfere with OWI communication. There are a few ways to fix this.

    First, please see the attached ppt for some EVM modifications that improve OWI reliability when communicating outside of the EVM.

    OWIFix.pptx

    Additionally, if you have a reverse current protection diode in the loop, and a capacitor between the PWR and FB+ pins (like the one shown in the 4-20mA application diagram from the datasheet), it can be helpful to decrease the capacitance. The datasheet application diagram suggests 100nF, but a 10nF capacitor will provide adequate protection from noise while improving the OWI signal integrity.

  • 0 in reply to Scott Cummins
    Intellectual 495 points

    We have two 22 ohm resistors, one each in the plus excitation and minus excitation on our circuit board, for EMC CE surge compliance.  We had found that shorting these resistors seemed to  allow the DAC to work.  For whatever reason, after making the suggested changes to the EVM board,  the DAC will not work even with the resistors on the circuit board shorted.  

    We did notice that the voltage directly at the transducer circuit board was reading 5.7 volts when not connected to the computer through the USB2ANY board.  However, when the USB2ANY board is plugged into the computer,  the voltage reading dips to 5.14 volts.  I'm not sure if this is due to the changes on the EVM but this may be related to the issues with the DAC.  Do you have any further suggestions?

  • 0 in reply to Lori Ferger52
    TI__Mastermind 31655 points

    Hello Lori,

    Are you able to use the additional voltage and Rloop settings in the GUI to adjust the OWI voltage levels being output by the EVM? This is important when connecting to an external board if you have any fixed voltage drops (diodes) or resistances in your current loop.

    Can you share your schematic? I would like to see the current loop connections up to the PGA305, and your connections to the EVM. Feel free to privately message me if you would prefer not to share publicly.


    Regards,

  • 0 in reply to Scott Cummins
    Intellectual 495 points

    I sent the schematic in an email.  Could you please confirm that it was received?

  • 0 in reply to Lori Ferger52
    TI__Mastermind 31655 points

    Hi Lori,

    I haven't received anything. Please try private messaging me. Just click on my username, then click on the "Connect" button on the top right of the screen to send me a message. You can attach the schematic that way.


    Thanks,