LMH1251: Can the unused inputs be left floating?

Nicholas Piegdon

Part Number: LMH1251

In my application, I'm using the YPbPr inputs exclusively. I wasn't able to find any guidance on whether the RGB input pins could be left floating or whether they should (or should not!) be tied to ground. The little "disconnected switch" triangle components in the schematic on page 2 of the datasheet seem to indicate it should be a non-issue and they can be left floating. Also, the half-dozen boards with an LMH1251 I was able to pull up in a Google Image search showed all of them with floating pins.

Would there be any advantage (lower power consumption?) to tying the unused pins to ground instead? Or is it perfectly normal operation to leave them floating?

More pointedly: the boards I ordered last week left them floating. Am I going to have to make a new board revision?

Thanks!
Nicholas

over 3 years ago

0 Nicholas Piegdon over 3 years ago

Prodigy 20 points

I found this old whitepaper ( https://www.ti.com/lit/wp/snla203/snla203.pdf that calls the video switching feature between the RGB and YPbPr inputs an "integrated 2:1 mux" which also seems to be more evidence that it's safe to leave the unused inputs floating.

I was still hoping to get an official confirmation that it's completely innocuous and that we aren't leaving anything on the table by not grounding them.

Thanks again!
Nicholas

0 Nasser Mohammadi over 3 years ago in reply to Nicholas Piegdon

TI__Guru* 88835 points

Hi Nicholas,

As you noted there is a 2:1 mux internal to the part that selects one input versus another. You can leave the un-used input floating. Please note cross talk versus frequency graph. As long as your incoming or selected signal is about 10 to 15dB better than cross talk graph we should be ok.

Regards,, Nasser

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LMH1251: Can the unused inputs be left floating?