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XTR111 Dynamic response

Nilesh Khupase
Intellectual 460 points
Other Parts Discussed in Thread: XTR111

Hello,

I want to generate a square wave current signal in the frequency range of 1Hz to 20KHz of peak amplitude 20mA. So i was thinking of using a XTR111 V to I converter with output current set to 20mA and then switching its output on and off using a MOSFET as a switch, which will simply connect load to XTR111 when on and disconnect it when off. This MOSFET will be driven by a Frequency generator generating the gate signal for MOSFET in the frequency range from 1Hz to 20KHz. Will XTR111 have any issues in switching its output current at 20KHz or lower ?

 

  • 0
    TI__Guru 62085 points

    Hello Nilesh,

    The XTR111 will likely not operate properly when used as you've suggested.  Disconnecting the output load from the XTR111 will cause the output amplifier in the XTR111 to saturate which will take a non-zero time to recover from.  This is typically called the "Overload Recovery Time" and is present in all amplifiers. 

    It would be much better to use the same MOSFET to create a zero to full-scale input signal to the XTR111.  Then you can expect performance similar to the images shown in Figures 31 and 32 in the XTR111 datasheet.  Both images show the rise time from 0 to 20mA is around 10us and the fall time is closer to 2.5us.  The period of a 20kHz waveform is 50us so you could expect the output to be near the full-scale values for roughly 37.5us of the 50us period. 

  • 0 in reply to Collin Wells
    Intellectual 460 points

    Hello Collin,

    Thank you very much for you reply, i do have have a requirement of generating a current signal which could be varied in the frequency range of 1Hz to 20Khz for my test fixture, so i will follow the way you suggested. 

    Thank you very much. 

  • 0 in reply to Nilesh Khupase
    Intellectual 460 points
    Hello Collin,
    I have one more question regarding XTR111, can i pull up Error flag pin to 3.3V logic high?, i read in the datasheet that it is being pulled up by weak internal pull up to 5V sothat it can be left NC...
  • 0 in reply to Nilesh Khupase
    TI__Guru 62085 points
    Hi Nilesh,
    Yes, you can use a pull-up to +3.3V. There is an internal weak pull-up to +5V, so an external pull-up will need to source the 1uA pull-up current which likely won't be an issue.