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LMH6554 - Diff DC level Bias and offset

Leo Champagne
Prodigy 140 points
Other Parts Discussed in Thread: LMH6554

Hello,

Our customer's issue on the LMH6554 :  In particular adding output offset by applying differential DC levels to biasing/termination resistors on the input. Second an application note has two unused pins connected to ground through resistors (application is single-ended supply’s). Need to know why they need to be connected to ground, if it is an AC ground, and if we need series resistors.

Hope to receive a response a feedback promptly.

Thx,

Leo

  • 0
    TI__Mastermind 22825 points

    Hello,

    It is possible to add output offset the way you have described. If you specify more details, I might be able to recommend a configuration for this.

    I'm not certain what you mean about the connections through resistors of unused pins. Again, please specify more details and I'll try and help.

    Thanks,

    Hooman

  • 0
    TI__Genius 13935 points

    The app note says that pins 11 and 14 have no internal connection but that they should be connected to ground through 0 Ohm resistors. 

    The resistor part is probably not necessary, a direct tie to ground should be fine.  The reason to ground the pins instead of letting them float is not clear from the documentation. 

    Sometimes bondwires are added to a package to provide isolation between pins.  In the case of the LMH6554 the no connect pins are between the power supply pins and the output pins.  It is likely that grounding those pins gives better performance by helping to keep load currents from coupling into the supply pins.