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DAC8740H: Profibus/Fieldbus schematic with the TM4C123

Gerard Rizkallah
Prodigy 55 points
Part Number: DAC8740H
Other Parts Discussed in Thread: PROFIBUS, , DAC8750, DAC8741H, DAC8742H, XTR117, OPA316, XTR115, XTR116, DAC161S997

Is there a reference schematic showing how to connect the DAC8740H to an MSP to support Profibus?

My end goal is to have, with the DAC8750, support for HART, Profibus, and Fieldbus on one PCB through multiple variants and zero ohms

  • 0
    TI__Mastermind 46290 points
    Gerard,

    DAC8740H is the UART variant of the three-device family (DAC8741H supports SPI, DAC8742H pin-selects UART vs SPI). So the UART_IN (pin 7) and UART_OUT (pin 10) connections to the MSP430 UART bus would be required along with CD (pin6) and UART_RTS (pin 8) connected to interrupts for communicating the state of the internal FIFOs and carrier detection / jabber inhibitor state.

    A similar connection scheme would be required for HART although the CD and UART_RTS pins change functions.

    For the most part there isn't anything too unique about operation in Profibus PA mode versus the other two protocols, so maybe I misunderstood your question?
  • 0 in reply to Kevin Duke
    Prodigy 55 points
    In Profibus/Fieldbus I would not use DAC8750 or the associated Loop circuitry, correct. I would DNP all of this and just use What would the two MOD_Out and MOD_IN for the 2-wire Profibus connection. The MOD_OUT parallel cap and clock freq would be only things needed to change? I want to make sure my thought process is correct. Thanks a lot for the prompt reply
  • 0 in reply to Gerard Rizkallah
    TI__Mastermind 46290 points

    Hi Gerard,

    Thanks, the question makes more sense to me now. You're not asking for the connections to the MSP430 but rather the entire schematic.

    Right now we are working on stack development for Foundation Fieldbus which will in turn drive our submission for certification to FieldComm Group. A specific Profibus PA certification is going to be our third effort, though being that Foundation Fieldbus and Profibus PA are based on the same PHY similar hardware is likely sufficient for compliance demonstration purposes.

    The SCH behind our current design is attached to this post, an image below for quick reference. Also attaching a TINA simulation for the same circuit.

    Of course this design is not a "Universal" transmitter supporting multiple protocols, so we have removed the DAC etc. You can however see our suggested filter components etc. here.

    You could choose to use something like an XTR115, XTR116, or XTR117 in place of the OPA316 circuit we have laid out in this proposal. You just need something to control the loop current which for FF and PA is just a DC current (not changing as in HART). As an aside, DAC8750 would not be applicable here because it is not designed to be compliant with a 2-wire loop architecture, instead this would fit in 3-wire and 4-wire sensor transmitter or PLC topologies.

    If you want to be able to support HART you will need the DAC so building off the previous comments you could add a DAC to drive one of the XTR devices, you could build something discretely, or you could look at something like the DAC161S997. Some examples of the XTR and fully discrete approach are discussed in the reference designs below:

    XTR:

    Discrete:

    DAC8740H_PAFF_Discrete Loop Powered Transmitter Simplified.pdf

    DAC8740H PAFF Discrete Loop Powered Transmitter Simplified.TSC