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Original question:

LMH1228: Unused pins connection

LMH1228: Defining IN/OUT pins

Luc
Prodigy 10 points

Part Number: LMH1228
Other Parts Discussed in Thread: LMH1208, LMH1297

I have a question regarding the LMH1208/LMH1228. 
There are several configuration pins to define the input/output path for video. When a path is defined, can the other pin be left floating?
Example: OUT0_SEL=H, SDI_OUT2_SEL=L; this will put the device in Dual cable drivers mode. Can we leave the host side loop-back OUT0p/n be left floating, or do you recommend defining these pins.

Same question regarding the LMH1297, if we configure SDI_IO as input and OUT0 as output, can we leave SDI_OUT floating?

  • 0
    TI__Guru**** 187761 points

    Hi,

    For LMH1228 unused OUT0p/n, you can leave these floating. Please make sure SDI_OUT2_SEL and OUT0_SEL are not asserted. There are internal pull up and these would disable these outputs.

    For LMH1297 unused SDI_OUT, you can leave these floating. And you can use pin control or through SMBus to power down the SDI-OUT.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Hi David,

    To enable SDI_OUT1 and SDI_OUT2 it need a H on OUT0_SEL and a L on SDI_OUT2_SEL. so I should not leave SDI_OUT2_SEL floating.

    In any case I rather have them hardware defined. So I will externally pull SDI_OUT1 up with a 1k (on top of the internal pull-up), and SDI_OUT2_SEL down with a 1k. As I understand from your previous message, in that case I can leave the loop-back output OUT0 floating.

    Please confirm my statement.

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    What about the LMH1297 IN0 and LOCK_N. Can these also be left floating?

  • 0 in reply to Luc
    TI__Guru**** 187761 points

    Hi,

    For LMH1228

    To enable SDI_OUT1 and SDI_OUT2 it need a H on OUT0_SEL and a L on SDI_OUT2_SEL. so I should not leave SDI_OUT2_SEL floating.

    Correct, SDI_OUT2_SEL is internally pulled high by default (SDI_OUT2 disabled) so you need to pull it low to enable SDI_OUT2.

    In any case I rather have them hardware defined. So I will externally pull SDI_OUT1 up with a 1k (on top of the internal pull-up), and SDI_OUT2_SEL down with a 1k. As I understand from your previous message, in that case I can leave the loop-back output OUT0 floating.

    Is this a typo "externally pull SDI_OUT1 up with a 1k (on top of the internal pull-up)", and should be OUT0_SEL? You can pull OUT0_SEL high to VIN using 1K and leave OUT0 floating.

    For LMH1297, 

    LOCK_N is a 3.3-V tolerant, open-drain output. It requires an external resistor to a logic supply.

    IN0 can be left No Connect since they have on-chip 100ohm termination.

    Thanks

    David

  • 0 in reply to David (ASIC) Liu
    Prodigy 10 points

    Hi David,

    Indeed it was a typo I mend pulling OUT0_SEL high with a 1k.

    As LOCK_N is an open-drain I assume it could also be left floating if not used?

    Thanks


  • 0 in reply to Luc
    TI__Guru**** 187761 points

    Hi,

    Even if LOCK_N is not used, I recommend using a 2k to 5k pull-up to the logic supply, since LOCK_N is an open-drain output.

    Thanks

    David