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New Question about ADS6243 power sequence

David Zhang16358
Expert 1860 points

Other Parts Discussed in Thread: ADS6243

In my design, the differential outputs of ADS6243 are connected with FPGA.

ADS6243 and FPGA are powered by different 3.3V supplies.

My question is:

If those two 3.3V power supplies can’t turn on at the same time, Could ADS6243 be latched up?

Can I connect a Schottky diode between those two 3.3V power supplies to avoid above problem?

 

Thanks.

  • 0
    TI__Mastermind 29220 points

     

    Since these are LVDS *outputs* of the data converter that are routed over to the FPGA, the data converter will not care if the FPGA is powered up before the data converter or after.  The LVDS outputs of the ADS6243 do not require that a device on the end of the LVDS traces be powered up or not.  Even if the FPGA is to supply the 100 ohm LVDS termination and that termination is not present until the FPGA is configured, that will not bother the data converter.  There will just be some reflections on the LVDS lines until the termination resistors are present once the FPGA is configured.  The only thing to be sure of is that the FPGA is not trying to *output* something onto those LVDS lines until it is finished configuration.  The FPGA pins that the LVDS go to must be either inputs or nothing during the time it is powered down or unconfigured.  They must not try to output something during that time.

    Regards,

    Richard P. 

  • 0 in reply to Richard Prentice
    Expert 1860 points

    Thank you for your great answer.

    If I put a diode between those two 3.3V, what is going to happen?

    Do any damages will happen?

    Thanks.

  • 0 in reply to David Zhang16358
    TI__Mastermind 29220 points

    I do not know - damage to what?  Depending on what direction the diode was installed in, when one of the power supplies powers up then the diode will also try to supply current to power up the other circuitry.  The power source may not be able to handle the current draw from the two loads, but i don't see how there would be any damage to the data converter.  When both power supplies are up, then i think the diode would not be doing anything at that point, so it would be not an issue at that time.

    Regards,

    Richard P.