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Searching for Constant current sourcing IC

Nshah
Prodigy 65 points
Other Parts Discussed in Thread: DAC7760, DAC7750, XTR110, XTR111, XTR300, TIPD153

Hello,

In our application, we required constant current source IC which can give output current between 0 - 20mA.

Also if I wish to design a circuit for the same above application using OPAM then how do I design , can anyone suggest me the circuit?

And how to precisely change current source using microcontroller to achieve current output between 0 - 20mA?

While searching for the same application I found DAC7760,So will it be helping for my application?

  • 0
    TI__Genius 11750 points
    Howdy Namita,

    Thanks for posting and welcome to the e2e forums! You are correct in your assessment, you can use the DAC7760 device, but before diving into the devices that provide this current output may I ask a few questions. What are the resolution and accuracy demands of the application -- will you require 12-bit or 16-bit resolution? Is the application going to fit in a 2-wire or 3-wire application? What is the end application?

    There are many TI designs that may fit your interest, which I've included below. The designs illustrate both a discrete and integrated approach in realizing the 0-20mA current.

    www.ti.com/.../slau502.pdf
    http://www.ti.com/tool/TIPD215
    www.ti.com/.../tida-00559
    www.ti.com/.../TIDA-00118

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    Prodigy 65 points
    Thank you Matt,
    Definitely I will go through all your suggested links, in fact I havetaken a quick look.

    And lemme give you a brief of my application in which, IC or circuit(which suits best to the application) should be managed by microcontroller and output requires in 0-20mA current ranges. The output requires for sourcing a precise current to a pressure valve( just FYI Pressure valve can handle/accepts 0-20mA current ).

    So for that, was thinking to use a low cost IC for easy handling but if not and a customize circuit designing would help to achieve this, it would be fine or help me how do I achieve precise and constant current between 0-20mA.

    Also as you asked for a resolution, so 12-bit resolution and 2 wire use for this application would be fine.

    Some more help needed to understand how XTR11X will help?
  • 0 in reply to Nshah
    TI__Mastermind 46290 points
    Hi Nshah,

    I think there was a bit of miscommunication concerning the vocabulary used here when referring to "2-wire" and "3-wire" systems. To clarify you can check out the blog linked below, maybe to an extent this is some TI jargon but similar is also documented in the ANSI/ISA-50.1-1982 standard. Being that your output can achieve a current output as low as 0mA, we are referring to a 3-wire system.

    e2e.ti.com/.../industrial-dacs-an-overview-of-analog-outputs-and-architectures

    With that in mind, the DAC7750 could be a very strong candidate and I think in terms of cost you will it is competitive compared to discrete approaches. The only case that I would suggest that you consider a discrete approach versus DAC7750 would be if the ranges offered were not acceptable or if there was some other gap in the fully integrated device. There is also a sibling device called the DAC7760 which also includes a voltage output stage.

    There are XTR devices which are similar to the DAC7750 in that they offer similar current output ranges, just without the DAC included. So you may be able to achieve a lower cost on a XTR device and replace the DAC with PWM if that were acceptable in your applications. There are tradeoffs to both and I think you'd find that the cost structures make sense for both. XTR devices similar to DAC7750 include XTR110, XTR111, and XTR300.
  • 0 in reply to Kevin Duke
    Prodigy 65 points

    Thank you Kevin Duke,

    Our system specification is as below:

    Application:
    We are using 0-20mA current generated by DAC7750 to control  pressure valve.
    we are not implementing HART. we just want only 0-20mA current source for pressure valve.
    for changing 1 PSI in valve, we will required around 300uA current variation.
    Our MCU is powered with 3.3V.

    For DAC7750,
    AVDD = 12V
    DVDD = 3.3V external
    Load impedance of pressure valve = around 250 Ohm
     
    we are using internal 5V reference for REF_IN
    we are not using internal generated 4.6V for DVDD, instead of we use external 3.3V.
    we are not implementing HART.
    we are going to use internal ISET-R resistor.

    Now the doubts are as below.
    1) Is it necessary to use ISOLATOR between MCU & DAC7750 interface for our application?
    2) we are not using current monitoring functionality & HART.So, what should be done with R3_SENSE &
        HART_IN pin? should they left unconnected or any other else?
    3) we will provide provision of external NPN transistor circuit as shown in datasheet at BOOST pin.
       but we will use it only if it is necessary(max. compliance voltage for our application will be 5V only),
       otherwise we will not use.
       In case if we not use then BOOST pin should be left unconnected or any other else?

  • 0 in reply to Nshah
    TI__Mastermind 46290 points

    Nshah,

    My responses to each question are below. Thanks for your reply.

    Nshah said:
    1) Is it necessary to use ISOLATOR between MCU & DAC7750 interface for our application?

    From the perspective of the DAC7750 alone there is no requirement for isolation.

    Including isolation would need to be a system-level decision for your end-equipment. DAC7750 is frequently used in PLCs, which it sounds like your end-equipment could be, and PLCs often feature isolation from the back-plane / controller to the analog front-end. The isolation scheme may be channel-to-channel isolated or group-isolated.

    Nshah said:
    2) we are not using current monitoring functionality & HART.So, what should be done with R3_SENSE &
        HART_IN pin? should they left unconnected or any other else?

    From a functional / requirement perspective these pins may be left floating.

    My recommendation would be to AC couple the HART_IN pin to ground as is shown in TIPD153 if your application environment is suspected to expose the design to extreme radiated emissions.

    Nshah said:
    3) we will provide provision of external NPN transistor circuit as shown in datasheet at BOOST pin.
       but we will use it only if it is necessary(max. compliance voltage for our application will be 5V only),
       otherwise we will not use.
       In case if we not use then BOOST pin should be left unconnected or any other else?

    If the BOOST pin is not in use the pin should be left floating. There is no risk on this pin from an EMC / EMI perspective if left floating, any other connection would impact signal chain performance.

  • 0 in reply to Kevin Duke
    Prodigy 65 points

    Thank you for your response, that really helped a lot!!