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LMH0394, Inductor selection

K S
Prodigy 60 points
Other Parts Discussed in Thread: LMH0394, SD394EVKDear Texas Instruments I am working on a new design where I am using SD-/3G-SDI video signaling. I have selected the LMH0394 cable equalizer, connected to my FPGA. In respect of the video cable/connector interface to the LMH0394, I read in the datasheet that there is recommended to implement a 5.6nH inductor (ref. i.e. fig. 5 in the datasheet). My challenge is to find recommended parameters on the inductor. Does Texas Instruments have a inductor recommendation, or parameters to pay attention to when finding a inductor to the design? Sincerely yours KS
  • 0
    TI__Expert 4400 points

    This 5.6 nH inductor is for the input return loss compensation network, and is necessary to meet the SMPTE return loss requirements.  The actual value of this inductor is dependent on the PCB design, but we have found that this 5.6 nH value works well on many designs including our evaluation board (EVM).

    The most important parameter to pay attention to when selecting the return loss inductor is the self resonant frequency (SRF).  Higher bandwidth inductors perform much better in the return loss compensation network, so I would suggest selecting an inductor with an SRF of at least 3 GHz.

    Also, for the best performance, the inductor physical size should be small (preferably no larger than 0402).  This allows you to use small-sized component pads to minimize impedance discontinuities in the input trace to the equalizer.

    The 5.6 nH inductor we use on our LMH0394 EVM (SD394EVK) is 0402 size with an SRF of 6 GHz and performs very well.  You can refer to this component, L1, in the SD394EVK bill of materials within the user guide, here:

    http://www.ti.com/litv/pdf/snlu064

    Gary Melchior