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ISO1212: iso1212 power dissipation

Masaharu Takahashi
Expert 4170 points
Part Number: ISO1212

Hi, Team.

i've been asked below question by customer.

1.is it ok if customer doesnt use Rthr?

2.how to calc power dissipation?

(Il..typ) * input(24V) = ??  

Il...2.25mA(typ)

in its datasheet, how do we calc 450mW?

i want to know its formula.(i want to know how wil Rthr influence on it since we can't know its formula)

  • 0
    TI__Expert 6955 points

    Takahashi-san,

    1.is it ok if customer doesnt use Rthr?

    The RTHR resistor sets the voltage thresholds (VIL and VIH) as well as limits the surge current. It is advisable to have it present even if it is simply to limit current from potential surges. Section 9.2.1.2 Detailed Design Procedure has more information on suggested values of Rthr based on system voltages.

    2.how to calc power dissipation?

    The power dissipated inside the ISO121x devices is determined by the voltage at the SENSE pin (Vsense) and the current drawn by the device I(INx+SENSEx). This current consumed will be dependent on Rthr and Rsense. This document contains more information in calculating these values. 

    I still owe you the exact formula in calculating powered consumed by the ISO1212. Please allow me to consult with another expert on the matter.

    Respectfully,

    Lucas

  • 0 in reply to Lucas Schulte9
    TI__Expert 6955 points

    Takahashi-san,

    This would be the formula to calculate power consumed by the ISO1212. Note that one needs to account for all input channels involved. 

    Also, the requirement of Rthr will really depend on the customer's voltage thresholds. Would you be able to provide the voltage thresholds needed?

    -Lucas

  • 0 in reply to Lucas Schulte9
    TI__Expert 4170 points
    thi, Lucas-san.

    thanks !

    for Rthr, even we recommend Rthr should be used , is there any problem if customer doesn't use it?
  • 0 in reply to Masaharu Takahashi
    TI__Expert 6955 points
    Takahashi-san,

    In order to determine if the customer needs Rthr we need to know what their desired voltage thresholds are. Would you be able to provide the voltage thresholds needed?

    Respectfully,
    Lucas