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XTR116: Vref current sourcing limitation

lien dayman
Prodigy 10 points
Part Number: XTR116

Regarding output Vref

spec sheet describes parameters (under test condition column) where Iref = 0 to 2.5mA

I wish to source current up to 3.8mA to increase my bridge circuit sensitivity.

is this recommended and what are my limitations?

https://www.ti.com/lit/ds/symlink/xtr115.pdf?ts=1711054401533&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FXTR115%253FkeyMatch%253DXTR115%2526tisearch%253Dsearch-everything%2526usecase%253DGPN-ALT

reviewing this app note seems to indicate currents >2.5ma are acceptable.  thoughts??

https://www.ti.com/lit/an/sboa575/sboa575.pdf?ts=1710965274101&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FXTR115%253FkeyMatch%253DXTR115%2526tisearch%253Dsearch-everything%2526usecase%253DGPN-ALT

  • 0
    Guru 298860 points

    The total current (300 µA for the XTR116 itself, and whatever you draw from it) must stay below the minimum loop current of 4 mA. The application note says that the requirement is for the total current consumption to be < 3.5 mA.

    The Vref characteristics for currents above 2.5 mA are not guaranteed.

  • 0 in reply to Clemens Ladisch
    TI__Guru 55466 points

    HI Iien,

    The total current consumption of the XTR current transmitter circuitry, that is, the current consumption of the XTR116 plus the consumption of the bridge sensor, and all the associated circuits driving the XTR116, must be less than 4mA.  

    The current consumed by the bridge sensor, XTR driving circuits, and XTR current consumption flows through current loop at the IOUT pin in the 2-wire current transmitter. The XTR116 quiescent current of 200uA typical (250uA max) at  ambient temperature of 25°C flows through IRET,­ leaving roughly 3.75mA for the remaining circuitry powered from VREF and VREG. Therefore, the output will not reach 4mA at the zero-scale input level if the external circuitry sinks more than 3.75mA at 25°C with V+ supply of 24V. 

    Therefore, the application note recommends to limit the total current consumption of the sensor and driving circuits to less than 3.5mA to account for the XTR current consumption variation across voltage supply and temperature variation.

    Also, the blog below discusses this topic in detail.

    2-Wire 4-20mA Sensor Transmitters: Sensor and Transmitter Current Consumption Limitations (Part 3)

    As you have show above on the data sheet electrical characteristics table, the XTR116 reference is only characterized to source currents up to 2.5mA.

    Thank you and Regards,

    Luis