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28377D cmpss hysteresis

Amtech
Genius 4585 points


Dear Sir,

Please clarify attached image which is found under cmpss section in datasheet.


Is hysteresis band is fixed to 12, 24, 36, 48 count with reference to fix 4096 count?

if DAC reference is set to 1000 count and i have selected 1X configuration then what should be band count? e.g. 1000 (set) to 988 (clear)

And if possible please attach schematic of internal comparator with hysteresis resistor.

Regards,

Maulik

  • 0
    TI__Mastermind 28275 points
    Hi Maulik,

    Yes, that is correct.
    The hysteresis in the CMPSS is implemented similar to a Schmitt trigger.
  • 0 in reply to Frank Ankapong
    TI__Guru 62975 points

    Maulik,

    To clarify, the F2802x/F2803x/F2806x family of devices use a Schmitt trigger scheme to provide hysteresis for the Comparators.  The Schmitt trigger feedback will impart some influence to high impedance signals at the comparator input.

    The hysteresis scheme for the CMPSS module is completely different.  Here, it behaves like a voltage offset that is internally applied to trip deassert transitions.  This hysteresis scheme is not expected to influence the comparator input signal.

    There is no schematic available to share with respect to the CMPSS hysteresis implementation.  Your description of the behavior is correct.

    -Tommy

  • 0 in reply to tlee
    Genius 4585 points

    Hi Frank and Tommy,

    Thanks a lot for clarification.

    I have one more doubt ,

    (Datasheet pg no. 111 revG)

    What is the meaning of " Hysteresis will scale with the CMPSS reference voltage" ?



    Thanks and Regards,
    Maulik Timbadiya

  • 0 in reply to Amtech
    Genius 4585 points

    Can anyone help me to understand this statement properly, " Hysteresis will scale with the CMPSS reference voltage"

    Thanks and Regards,

    Maulik

  • 0 in reply to Amtech
    TI__Guru 62975 points

    Maulik,

    Sorry that we missed your previous post.

    The CMPSS hysteresis scheme uses the CMPSS-DAC as the reference for determining how much hysteresis to apply.

    For example, the datasheet indicates that the 1X hysteresis setting will apply roughly 12 CMPSS-DAC LSBs of hysteresis.

    The CMPSS-DAC uses either VDDA or VDAC for its voltage range reference, therefore the step-size of the CMPSS-DAC LSB scales with the reference voltage supplied.

    So:  CMPSS Reference Voltage -> CMPSS-DAC -> Hysteresis

    -Tommy