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PGA305: Issues with OWI activation related to DAC

Matias Ljøen
Prodigy 50 points
Part Number: PGA305

Tool/software:

Hi,

We are currently having some issues with OWI activation that seems to be related to DAC in 4-20mA mode.

After OWI activation when we are trying write to DAC we found that we can not write directly the DAC value we want, we have to increment it slowly by around 1000 at the time.

What happens then is that the sensor increases mA by a little, but then stops before it reaches the mA it should and also we can not activate OWI anymore or communicate.

The sensor has to be powered on and off. Then the mA goes down and we can communicate again.

Is there some kind of fix for this?

Another issue is that if we accidently upload the wrong calibration coefficients to the sensor, the mA goes to around 30mA and we can no longer communicate with sensor using OWI and OWI activation is not possible.

  • 0
    TI__Intellectual 2015 points

    Hi Matias, 

    Are you able to capture the OWI signals with an oscilloscope or a logic analyzer? In particular, could you capture PGA305 VDD and the OWI RX signal (I assume you have an external microcontroller reading the OWI signals)? 

    Additionally, are you using a TI EVM? If not, can you please share a picture of your schematic?

    Thanks,

    Maggie

  • 0 in reply to Maggie Lee
    Prodigy 50 points

    Hi,

    I am using PGA305EVM-034 with an external microcontroller

    Here's the scope shot of PGA305 VDD and OWI RX signal.


  • 0 in reply to Matias Ljøen
    TI__Intellectual 2015 points

    Hi Matias, 

    OWI can be fussy in current mode. Since the OWI activation and TX levels have such narrow bounds, if you have too much current flowing through the loop, then your OWI signals may go outside of those bounds. That is probably why you are not able to communicate when you load the wrong coefficients. 

    In the PGA305 GUI, there is a way to adjust the OWI signal. Changing Additional Voltage will change the offset of the signal, and changing Rloop will change the amplitude of the signal. 

    When you are unable to communicate with the device, can you try adjusting the OWI signals to re-establish communication? You will need to use an oscilloscope to read the voltages. 

    Additionally, when you lose communication with the device, do you re-send the activation pulse in an attempt to re-establish communication?

    Are you using the DAC while the microcontroller is in reset? Does this issue occur with multiple devices or just 1?

    Thanks,

    Maggie