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DS90UB935-Q1: VDDX Ferrite Bead DCR

David Shumate
Expert 7785 points
Part Number: DS90UB935-Q1

Hi Team,

On page 70 of the datasheet for the 935 and on the datasheet for the 953 there is a block diagram for the 1.8V VDDX ferrite beads with a recommendation that the DCR needs to be under 25mohm:

Looking at the EVM for the 953 though the BLM18AG102SN1D is used and this has a DCR of 600mohm:

Is the only concern for the DCR that we meet the recommended supply voltage tolerances?

Is there any other concern for having a DCR higher than 25mohm?

Thanks,

David

  • 0
    TI__Expert 3390 points

    Hi David,

    That is correct, it is mainly for meeting the voltage tolerances and avoiding a high voltage drop across that ferrite bead. I'm not sure at the moment as to why they chose that one, perhaps because it met the impedance recommendation and that was the best option at the time but I'll look into that.

    Regards,
    Mandeep Singh

  • 0 in reply to Mandeep S
    TI__Expert 3390 points

    Hi David,

    I wanted to follow up with you and tell you that when discussing FBs in power application, it is better to target a lower DCR (25Ohm). When targeting PoC network applications, it is better to target a higher impedance >1K versus DCR, so the system acts as an open and doesn't cause issues to the high speed signal. Lower DCR in power will provide a lower voltage drop which is better in that situation versus the effects of high Z. I think they selected that particular part as it provided the best option at that time. If you are able to find something that fits both of these criteria's, that would be best. Otherwise, you can use what we provide.

    Regards,
    Mandeep Singh