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6657 Reserved pins

Paul Burrell
Prodigy 160 points

On the EVM board for the 6657, there are a group of resistors that connect RSV01 to RSV19 to the appropriate GND/VCC1V8 connections.   Most of these resistors are labeled as NU which indicate "NO USED" or "NOT INSTALLED".   The datasheet indicates that these pins are "Reserved - leave unconnected".   On the development board, there is actually a component installed.

Two questions...

1. Do the resistors need to be included in the design even though the datasheet indicates that the should be left unconnected?

2. Can the resistors / PCB land patterns be safely removed from a design?   Is there any reason (test/debug) that they might be useful in the future?

Thanks,

Paul

  • 0
    TI__Intellectual 1585 points

    Hey Paul, 

    To answer your questions, 

    1. Yes. They may be reserved to customers, but they might have some significance for debugging internally. It could either be a designing check prior to securing the devices to be sent out, to debug it whenever the customer has an issue and we want to recreate it on our own versions, and most of them, honestly, are uneventful pins that don't really help customers design in any way (they usually cause more confusion because they have little effects for you). To leave it unreserved would as I said cause confusion, or to reveal some things we have to keep lock in and key legally. 

    2. They might be useful if you have an issue with it and you send it back to TI to be checked. However, if you're very very certain then I guess you can remove them. I would, however, not. Sometimes there are resistors within the NU class which are backup resistors to prevent the current from going to your device if it is sensitive, or for other design back up system. 

    Regards, 

    Kat Kelsch 

  • 0 in reply to Katherine Kelsch
    TI__Mastermind 46460 points

    Paul,

    As Kat said, leaving the test resistor footprints will not cause harm.  The RSV pins do allow some test access in extreme cases.  However, this is not a requirment.  The requirement is that you meet the requirements listed in the datasheet.

    The EVM should not have any resistors installed into the locations marked NU.  Are you sure that you are looking at the correct locations?

    Please note that the EVM does have an error in the schematic for RSV8 and RSV10.  As shown in the Data Manual, RSV10 needs to be connected to ground and RSV08 should be left floating.  We need to get the EVM schematic on the web corrected and the Known Issues document updated.  There is no functional impact other than slightly higher leakage with the incorrect EVM connections.

    Tom