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LT8390 Current Sense and Limiting Resistor Selection


I am planning to use LT8390 Switcher in my application. I am trying to understand the applicability and usage of Rsense and Ris resistors. The LTPowerCAD designs let Ris be optional, and their values do not seem to make any difference to the design. However the datasheet makes it clear that Ris is used for output / input current limiting.  We are mainly concerned with designing for output current draw and limiting. So my questions are as follows:

1. Does Rsense set the max output current draw in Buck or Boost mode and Ris set the output current limit ?

2. Is the output current limit usually set higher than the max output current draw ? Is there a % increase we need to factor in for the current limit ?

3. As per datasheet, if current limit function is not used, the ISP and ISN pins should be shorted to Vin, Vout or Ground. Since we are mainly worried about the output current draw, does it mean Ris is 0 and ISP-ISN pins are connected to Vout when current limit function is not used ?



  • Hi AB,

    1. From what I understand of the datasheet, Rsense measures the current flowing through the inductor which is also dependent on the output current (see equations on pages 19-20). Ris sets the output current limit. 

    2. I believe output current limit should be set to the max output current draw. 

    3. If current limiting function is not used, ISP and ISN pins should be connected to either Vin, Vout, or ground. There should be no Ris connected.