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LM15851: Driving LM15851 diff SYNC~ input with an LVDS driver

vic zap
Intellectual 740 points
Part Number: LM15851

Hi!

As I've seen in LM15851EVM, SYNC~ input of the LM15851 is directly driven by TSW14J56's FPGA diff output. Is that output is configured as an LVDS output?

If so, it doesn't meet common mode voltage requirements for the LM15851 SYNC~ input specified in the datasheet, as LVDS driver has common mode voltage around 1.2V and required range is 0.64V to 1.1V (Recommended Operating Conditions table, p.10).

Have I missed something? Can you give some comments?

Best regards, Vic.

  • 0
    TI__Mastermind 44560 points

    Hi Vic

    While the SYNC~ differential connections are available on the LM15851EVM and TSW14J56EVM, we actually use the ~SYNC_SE single ended version of this signal. This signal is on pin H31 of the FMC connector. A resistor divider is used to match the logic level between the TSW14J56 2.5V CMOS output and the LM15851 1.9V LVCMOS input.

    The single ended signal is fast enough to meet the requirements of ~SYNC timing and using it eliminates the need to match the common mode levels between the TSW14J56 FPGA outputs and the LM15851 differential ~SYNC inputs.

    Best regards,

    Jim B

  • 0 in reply to Jim Brinkhurst1
    Intellectual 740 points

    Thanks a lot, Jim! Now it's clear.

    Best regards,

    Vic.