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XTR 111 Giving a current pulse after 8-10 second of switching off

Sujit Kr Nayak
Prodigy 60 points
Other Parts Discussed in Thread: XTR111

I have an issue with the XTR111 voltage to current converter. It is configured as per the datasheet. The (OD) Pin 9 is directly connected to GND. Regulator is not used also Output Failure is not used in the design. All the values of Caps & resistors are same as per the datasheet. It is used to give 4-20mA Output for  400mV - 2V input to the XTR111 from DAC MAX538. 

The problem: After switching off the power supply to the circuit, the loop current is coming down to approx 0mA from the lowest value (i.e. 4mA) and after few second approx. 10 second it is giving a current shot of 8-10mA. I probed the 24V supply to the XTR111 as well as the 5V supply to the rest of the circuitry, and both are coming down to 0V just after 1-2 second of the switch-off. I wonder from where the current burst is coming with out any supply voltage. Is it due to any capacitor discharge ? How this can be avoided?


This problem is always triggering the alarm (which is a auto triggered, but manual reset), so at every time the System switches off, it raises an alarm.  

  • 0
    TI__Mastermind 21646 points

    Hi Sujit,

    I am moving your question to the Precision Amplifiers forum so that it would get the right visibility and support. Hopefully this team will be able to get you an answer shortly.

    Thanks,

    John

  • 0 in reply to John Griffith
    TI__Guru 63225 points

    Hello Sujit,

    Thanks for contacting us, this is an interesting issue we haven't heard of before.  Would you please share your schematic with us so we can verify your connections as well as the external components chosen for the MOS devices and any other external circuitry connected?

    Good work probing the XTR111 V+ supply voltage and VREG output voltage, this information is helpful.  Could you also probe the "IS" and "VG" signals that connect to the external PMOS device during/after power-down?  I'm not sure why/how they are becoming active but the "VG" signal may be causing the PMOS to turn ON and source current unexpectedly.  

    Let us know what you find.