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PGA305: PGA305

Blaise Pascal ARAKAZA
Prodigy 20 points
Part Number: PGA305 
Hello everybody,
I have a question regarding configuring an external PGA 305 to the PGAXX EVM using OWI cominucation.
I can read data from my PGA305 when the PGA305 is in the PGAXXxEVM. I would like to do the same on a PGA305 already on a circuit.
Apart from jumper J12, should the other jumpers on the PGAXX EVM be closed?
Following the assembly in figure 7 of the PGAXXXEVM, I am supposed to read/write in my PGA305 by OWI communication.
How can I communicate with my PGA305 already included in a circuit? The length of the wire from VDD and GND to the OWI pin could be a problem?
Thank you.
  • 0
    TI__Intellectual 2010 points

    Hello, thank you for your E2E post. We have sent you a private message with some additional questions.

  • 0 in reply to Kyle R. Stone
    TI__Guru** 113765 points

    Hi Blaise Pascal ARAKAZA,

    Welcome to the E2E forum!  For the EVM the OWI interface uses the voltage applied to the EVM for communication.  You should be able to remove the PGA305 device from the EVM and connect your external device to TP20 (+) and TP45 or TP46 (-).   So you should have the same setup when the PGA305 is on the EVM as you do what it has been removed.

    For OWI communication, the activation requires that a higher voltage be applied to the EVM than the PGA305 may normally require.  Figure 14 in the EVM user's guide shows the power distribution.  The 7.5V regulator supplies the required voltage for the OWI activation.  This means that the banana jack power be at least 10V.

    Blaise Pascal ARAKAZA said:
    The length of the wire from VDD and GND to the OWI pin could be a problem?

    I'm not sure what you are truly asking.  What is the OWI pin that you are referring to?  OWI works by modulating the voltage/current of the supply.  So unless the supply wires are creating a significant voltage drop there shouldn't be an issue.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    I Thank you Bob, This resolved my issue. However I still have a problem with the PGA voltage Output. 

    1) I configured the EEPROM correctly, choosing "DAC" gain different from no gain. Despite this, I have nothing on output.

    I choseed the voltage mode .

    What to do ?

    2) I just want to measure a differential voltage at the terminal of an unbalanced wheastone bridge without variation in temperature or pressure. Should I use "compensation mode" or "digital mode" is enough. what is the difference between the two modes?

    Thank you.

  • 0 in reply to Blaise Pascal ARAKAZA
    Prodigy 20 points

    Hello Bob ,

    I managed to configure the output voltage gain by enabling the TEST_MUX_DAC_EN and the ox0101 value on DAC REG0
    in DAC configuration and I have the correct value at the output. 
    However, as soon as I cut the supply voltage the registers reset and I lose the output gain. How to solve this problem?
  • 0 in reply to Blaise Pascal ARAKAZA
    TI__Guru** 113765 points

    Hi Blaise,

    The PGA305 has both EEPROM and volatile memory for the control and status registers.  Table 20 in the datasheet lists those registers that are EEPROM.  Unfortunately DAC_REG0 is volatile.  Generally you would calibrate the system and the DAC output is then based on the TC and NL coefficients.  If you do not intend to use the TC and NL calibration values you can follow equation 8 on page 44 of the datasheet.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points 
    Thanks Bob,
Thank you for your answers. They help me move forward on my project. I have another question about the PGA 305.
Do you have versions that work over a wider temperature range? Notably which goes down to -55°C? or T.I plans to produce them?
Thank you.
    Blaise P
  • 0 in reply to Blaise Pascal ARAKAZA
    TI__Guru** 113765 points

    Hi Blaise P,

    Unfortunately we do not have PGA devices of this type that have extended ranges nor are there plans to create devices beyond the current temperature specifications.

    Best regards,

    Bob B

  • 0 in reply to Bob Benjamin
    Prodigy 20 points

    Thank you Bob .

    However , I still have problem with the PGA305 DAC output .

    I'm coming back here to see if I could find a solution to my problem with the PGA 305. When I configure the Analog config EEPROM as in the image below in DI. I manage to modify all the registers, for example VBRDG_CTRL (I can have 2.5,2, or 1.25 at the terminal of my wheatstone bridge). On the other hand, I cannot see any voltage at the output of my PGA (analog output). By having configured my PGA305 as below for example. what is the problem?

    Thank you.

  • 0 in reply to Blaise Pascal ARAKAZA
    TI__Guru** 113765 points

    Hi Blaise,

    You can control the output manually in the digital interface, but if you want to see the DAC output change automatically you will need to be in Compensation mode which takes the M0 out of the reset state.

    Best regards,

    Bob B