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ADS1281: Vih threshold

David Lopez38
Prodigy 10 points

Part Number: ADS1281

The ADS1281 has a digital Vih requirement of 0.8 * DVDD.  Therefore if the DVDD is at 3.3V, that means the minimum threshold is 2.64V (nominal...could be higher with a 5-10% tolerance on the supply voltage).  But, the JEDEC for LVTTL (3.3V) is 2.4V.   So why is this digital interface, that is a 3.3V powered device, have a higher threshold than the standard?   Or, is the ADS1281 datasheet very conservative and the ADS1281 can operate properly over temperature when being driven by a JEDEC LVTTL validated digital device, who's minimum output voltage can be 2.4V?

  • 0
    TI__Mastermind 44760 points

    Hi David,

    The ADS1281 digital logic level specifications are conservative; however, I don't know the margin on this spec. I'll see if I can some more information from the designer.

    Best Regards,
    Chris

  • 0 in reply to Christopher Hall
    TI__Mastermind 44760 points

    Hi David,

    Are you currently using a LVTTL driver?
    Given the choice, it would probably be safer to use an LVCMOS driver. However, if you're already using a LVTTL driver we could try running some corner simulations to get a better idea of the worst case Vih requirement. Let me know if that would be useful to you.

    Keep in mind there will likely be some additional margin on the driver side, as well...The  2.64V LVTTL 2.4V minimum output voltage is specified with a 2 mA load. The load presented by the ADS1281 digital inputs will likely be on the order of a few uA.

    Best Regards,
    Chris