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XTR111 EF internal pull up current

Thiago Finotti
Intellectual 580 points
Other Parts Discussed in Thread: XTR111

Hello,

I am designing a thermal controlling system, and a current transmitting system as a block of it, designed around XTR111. Please see attached.

1) I have thought of using a LED for visual signing whenever EF goes low. So I have used the circuit as connected to EF. I have not physically implemented it, and couldn't find any macro for XTR111 so far. Datasheet mentions that:

Internal pull-up current is 2uA. I didn't get what it means, is it limited to 2uA? If yes, current flowing though R28 won't be enough to turn M1 on and the circuit won't work. I am just checking, although this LED driving circuit came from EVM, I will have no time to change it after PCB is produced.

2) In EVM file (attached, pg 6), I could see an equivalent for R_XTR IN FALSE, grounding the input voltage. It is not present in the datasheet. I assume it intends to improve SNR by grounding, is that correct?

Thank you,

Thiago

0511.COND XTR111.pdf

8306.XTR111 Evaluation Module User's Guide (Rev. C) - sbou048c.pdf

  • 0
    TI__Genius 12345 points

    Thiago,

    1) 2uA is the weak internal pull-up current but does not indicate how much current the pin can sink. Weak internal pull-ups are used to hold the pin at a known state it if its not connected to external circuitry. Knowing the value of the internal current can inform the designer on how long it would take this pin to return to a logic high output if an external pull-up was not used and there was some capacitance at the EF node. 

    From the spec table for the part we can see that the EF pin is able to sink 2mA and still maintain a Vout low of 400mV:

    With the 100k external pull-up that you show in your schematic, the EF pin will only have to sink 50uA at most, which is well within the capabilities of the part.

    2) I believe the purpose of R10 on the EVM is to provide a grounded input impedance for the PCB in the event that the input level shift jumper (J3) is not installed. 

  • 0 in reply to John Caldwell
    Intellectual 580 points

    John,

    Got it!

    Thank you!


    Thiago