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DS250DF810: Shared pull-up resistor on EN/SMB pin

Antony Lin
Genius 13480 points
Part Number: DS250DF810
Other Parts Discussed in Thread: DS125MB203, DS125BR401A, DS125BR800, DS280DF810

Hi,

We want to share one pull-up resistor at EN/SMB pin among chips in two combinations as below.  Please suggest which resistor value we should use.

  • Combination 1: DS250DF810+DS250DF810 (pull-up to 2.5V)
  • Combination 2: DS125BR800+DS125MB203+DS125MB203+DS125MB203+DS125MB203+DS125BR401A+DS125BR401A (pull-up to 3.3V)

Thanks!

Antony

  • 0
    TI__Mastermind 43795 points

    Hi Antony,

    The normal pull-up resistor for a single device is 1000 Ohms.  If two inputs are tied together, the value of the pull-up resistor is divided by 2.

    For combination 1 above:  2 DS280DF810's ENSMB pins = Use a single 500 Ohm resistor  

    For combination 2 above: There are 7 seperate devices.  If the ENSMB pin from each device is connected together the pull-up resistor value should be 1000/7 or approximately 142 Ohms.  Any value < 150 Ohms would work well.

    Note: I would not try to combine combination 1 and 2 together with one resistor for all the devices.  The different power rails will make the ENSMB level difficult to determine as the supplies both ramp up.

    Regards,

    Lee