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66AK2H12 bulk and bypass caps

Scott Greeley1
Intellectual 585 points

Other Parts Discussed in Thread: 66AK2H12

We followed the Eval board schematic for the quantity and values of bulk and bypass capacitors for the 66AK2H12 in our design.     However, the newly released Keystone II H/W Guide recommends quite a few more and larger capacitors (Table 3) than the Eval board has.  E.g. there are 8 1500uF caps for CVDD and 4 for DVDD15.    We only have 1 each on those.      

What issues we will have, if any, with our design by only following the Eval board?   We're in final assembly of our card now, so we can't change our design.  

thanks,   Scott

  • 0
    TI__Mastermind 42545 points

    Hi Scott,

    There isn't an easy answer to that question. The selection of capacitors for your design must be part of your power distribution network (PDN) analysis. Power supply design, layout, board material, capacitor selection and capacitor positioning all contribute to the impedance profile of your board across the range of frequencies.

    The values listed in the hardware design guide are based on a board we developed to characterize the high speed interfaces for the K2K and K2H devices. That board was designed to handle some of our worst case scenarios, so the capacitor values were provided as a template as a solution for customers that have not performed their own PDN analysis. The EVM board was simulated separately and it was determined that fewer of the larger values were needed based on the layout of the power planes and the placement of the capacitors.   Without a complete PDN analysis, I can't tell you whether that lack of those extra capacitors will cause any issues for you design.

    Regards, Bill