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XTR117: Internal RLim value, Stabilization, and Internal Regulation

JP
Expert 3891 points

Part Number: XTR117

Hello PA Team,

I have a customer who is looking to use the XTR117 for their application. They have a number of questiions on the internal workings of the device that are not answered in the datasheet, so I wanted to see if we could provide some clarification.

  1. What is value of RLIM (internal resistor) between pins 3 and 5?
  2. What is the max output voltage on pin 6 without opening the internal transistor?
  3. Currently, their output has more gain in the control loop than what is coming from Q1. How can they make sure that the final regulator is stable? Do we have a spice model of the XTR117 so that we can simulate it?
    1. For the Spice Model I found E2E Post with an ideal simulation. 
  4. Is the op amp rail powered by the 5V internal regulator or the input voltage?

If you need clarification on any of the questions let me know. 

Best Regards,

Javier Palomo

  • 0
    TI__Guru 65025 points
    Hello,

    1.) It's about 100 Ohms
    2.) Not sure what's being asked here. There is a 1/4 resistor divider between the output of the op amp and the base of the internal BJT. Therefore with the external BJT connected the internal BJT doesn't see enough voltage to meet the Vbe requirement.
    3.) Unfortunately there's only the unofficial one that you found. Could you post a more complete schematic so that we can take a look at what the customer is describing?
    4.) The op amp is powered between V+ and IRET.