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THS4509EVM

Eric Miller
Prodigy 40 points
Other Parts Discussed in Thread: THS4509EVM, THS4509, THS4513EVM, THS4511EVM, THS4508EVM

I recently purchased a THS4509EVM board (thru Digikey).  In contrast to the schematic shown in the THS4509 data sheet, 69.8 ohm resistors R1, R2 are tied to VS-, not ground.  Is there an error on some eval boards, is the data sheet schematic incorrect?

Thanks for your timely response

  • 0
    TI__Genius 13335 points

    Hello Eric,

    Thank you for pointing this out. The schematic in the datasheet is correct and should match the EVM. R1 and R2 should be tied to ground. There was a problem with the re-build where the blind vias were misconnected. The device should still function properly if you operate it with a single supply of 5V (Vs- tied to ground).

    We have notified our distributors to pull back these EVMs so we can correct the error.

    Another option is to use one of the other EVMs (THS4508EVM, THS4511EVM, THS4513EVM) as these have pin for pin compatible ICs. Or you can build your own PCB.

    We apologize for the inconvenience.

    -Luke

  • 0 in reply to Luke LaPointe
    Prodigy 40 points

    Luke:

    On the EVM I received, the bottom ends of R1/R2 were tied to VS- (less than 1 ohm), rendering the board non-functional no matter what supplies were used. Obvious solution was to remove R1/R2 and proceed.

    Thanks,

    Eric

  • 0 in reply to Eric Miller
    TI__Genius 13335 points

    Eric,

    R1 and R2 are needed to properly terminate the source and balance the inputs. You may notice poor S11 if you remove these resistors. Another option is to "teepee" a series cap to ground so that the AC matching is still present and everything is balance and happy.

    I've attached a simulation of what I've described below.

    6445.THS4509 - VEE Shorted.TSC

    Let me know if this helps.

    -Luke

     

  • 0 in reply to Luke LaPointe
    TI__Genius 13335 points

    Eric,

    The other option is to use a slightly larger package resistor for R1 and R2, say 0603 or 0805 (instead of 0402) and tie to the "ground side" of c9 and c10.

    If you notice, the negative supply is not shorted to ground, just that particular node. If you can "hop" over it with a larger package resistor, then you can still tie it to ground as was originally intended.

    -Luke