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RM44L920: Test Pin - purpose and grounding method

Josh Heiner
Intellectual 860 points
Part Number: RM44L920
Other Parts Discussed in Thread: LAUNCHXL2-RM46

Hi,

I'm wondering about the test pin (in the case of the RM44L920APGET part I'm using, pin 34).

1.) What is its purpose?  I can't seem to find an explanation.  It may be in the manual or TRM somewhere, but just searching for the string "test" yields a huge number of hits due to all of the safety-related BIST functionality and such.

2.) The datasheet says this about the pin (my emphasis): "This terminal must be connected to ground directly OR via a pulldown resistor."  Okay - which is it then?  If there's no functional difference between connecting it to ground directly and pulling it down with a resistor, why would I waste the cost and board area of a resistor?  I was going to ground it directly until I noticed that my dev kit (the LAUNCHXL2-RM46 board) has it pulled to ground through a 2.2k resistor.  Why would I want to do that, or why not?

Thanks,

Josh

  • 0
    TI__Mastermind 49120 points

    Hi Josh,

    There are various test modes (e.g. ATPG scan) used during production test that need to set this TEST pin high. Some of these modes are not functional modes, and are not required / supported in application use. These test modes are for TI use only,  so you can tie the TEST pin to ground directly on your PCB. We have connected it to GND via a resistor on the LaunchPad so that we still maintain the ability to use these test modes if required.

    Regards,

    Sunil

  • 0 in reply to Sunil Oak
    Intellectual 860 points

    Perfect.  Thanks for the quick response Sunil!

    Josh