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DAC161S997EVM: Achievable sampling rates

Patrick Palmetshofer
Prodigy 20 points
Part Number: DAC161S997EVM
Other Parts Discussed in Thread: DAC161S997

Hello,

we are thinking of buying a DAC161S997EVM for controlling a 4-20 mA valve on a test stand with LabVIEW.

I found a chart on settling times on page 7 of the datasheet, but as the evaluation module uses capacitors with a far greater capacity than 1 or 2 nF, I am confused about how to read this. I could not find any data on this here either.

So essentially my questions are:

Can I use the DAC161S997EVM for a 4-20 mA valve at 10 Hz?

Can I use it at 100 Hz?

Thank you very much,

Patrick

  • 0
    TI__Guru 52663 points

    Hi Patrick,

    Thanks for using the e2e forums!

    The DAC161S997EVM uses the 'HART Adaptation' capacitor values (C1 = 390nF, C2=220nF, C3=1nF).  A 4-20mA transition is approximately 2/3 of the 0-24mA range, about 44000 code steps.  Looking at figure 4 in the DAC161S997 datasheet you can see that at that many code steps the settling time is about 100ms.  This means that you just barely be able to operate at 10Hz (assuming the full 16mA transition every update).  If you are not using the HART input, you could replace the capacitors with 1nF values, then be able to operate at over 100Hz.  

    See the attached TINA simulation to look at the AC response of the filter.

    Thanks!

    Paul

    DAC161S99 Filter Response.TSC

  • 0 in reply to Paul_Frost
    Prodigy 20 points
    Hi,

    Thank you for the information!

    We have now purchased the board and are having slight troubles. The transition times seem good, although the delay due to write/read operations is around 1 second. Is it possible to operate the board at baud rates over 9600 via the USB interface? (Assuming the limited baud rate to be the issue)

    Thanks again!
    Patrick
  • 0 in reply to Patrick Palmetshofer
    TI__Guru 52663 points

    Hi Patrick,

    I am happy to hear that the slew rates look good.  

    I think the delays in the software are primarily due to the PC side software, as well as the abstraction of the communication PC->USB->MCU->DAC.  The DAC161S997EVM features a JTAG header for MCU debugging and programming, with the goal that you could implement your own firmware to test the device.   I think that if you desire to have fast updates (>1ksps) I think that creating your own firmware is the way to go.

    Thanks!

    Paul