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XTR110

Michel Villeneuve
Prodigy 30 points
Other Parts Discussed in Thread: XTR110, XTR111

Hello,

we would like to convert a 0-4.096V to 4-20 mA.  Before to invest time on this design could you answer these questions about the circuit published in the XTR110.pdf figure 5 :

- If we modify the connecton for a 0-5 V input, will it be possible to adjust the output to 4-20 mA from a 0-4.096 V signal ?

- What will happen if by error (we design product for technical school) a +24Vcc is connected to the output instead of RL?

 

Finally, do you have a suggestion for a low cost isolator circuit for a 0-5 V low power signal ?

 

Thank you,

 

Michel

 

  • 0
    TI__Mastermind 27715 points

    Hello Michel,

    Thank you for your interest in the XTR110. However, based on your application I recommend a solution based on the XTR111 instead.

    While I believe that with properly-selected potentiometers, and time spent adjusting them, you would be able to achieve 4-20mA with 0-4.096Vin on the XTR110, an simpler and more cost-effective solution is to use an input offset circuit with the XTR111. Using a 4.096V reference voltage (which it sounds like you already have available for your input DAC), the simple circuit shown below taken from the XTR111 data sheet generates Vfs/5 = 0.8192V when the DAC output is zero to ensure the proper output span. The transfer function of the XTR111 is Iout = 10*(Vin/Rset), so with an Rset of 2.05k the output is 10*(0.8192V/2.05k) = 4mA and 10*(4.096V/2.05k) = 20mA. Precision resistors for Rset, R1, and R2 are recommended to ensure accuracy.

    Using the external current limit circuit given on Figure 37a, if 24V is connected to the output a short circuit current of only ~50mA will flow through the part. This is well within its handling range so after correcting the connections the XTR111 should operate normally.

    If you like, I can ship you an XTR111EVM to use for evaluation.

    Finally, can you give me more details about the application of your 0-5V low power signal?

    Best regards,

    Ian Williams
    Linear Applications Engineer
    High Performance Linear