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ADM13307 - Can the Sense Pins Be Driven When Unpowered?

Question asked by flyerrap18 on Nov 5, 2013
Latest reply on Nov 19, 2013 by Ren

    Good afternoon.  I have a customer using the ADM13307-4ARZ in a supervisory function.  The maximum voltage that the SENSE pins can see are as follows:

 

          SENSE1_MAX_INPUT = 1.1V + 5% = 1.155V (not sure if SENSE1 and SENSE3 are backwards and have asked for verification)

          SENSE2_MAX_INPUT = 1.8V + 5% = 1.89V

          SENSE3_MAX_INPUT = 2.5V + 5% = 2.625V

 

     where VDD is 3.3V +/- 5%.  Now, with a reference voltage of 0.6V (Figure 2) and looking at the "Absolute Maximum" ratings for the "Sense" pins on page 6 of the data sheet, the equation given yields the following as the absolute maximum voltage allowed on each sense pin where VIT1 = 2.25V, VIT2 = 0.6V and VIT3 = 0.6V according to the ordering guide on page 11.

 

                        MAX_SENSE - [(VDD + 0.3V) * VIT] / VREF → from page 6

 

                        MAX_SENSE1 = [(VDD + 0.3V) * VIT1]/VREF1 = [(3.3V + 0.3V) * 2.25V] / 0.6V = 15V  so good here

 

                        MAX_SENSE2 = [(VDD + 0.3V) * VIT2]/VREF2 = [(3.3V + 0.3V) * 0.6V] / 0.6V = 3.6V so good here

 

                        MAX_SENSE3 = [(VDD + 0.3V) * VIT3]/VREF3 = [(3.3V + 0.3V) * 0.6V] / 0.6V = 3.6V so good here

 

      The ADM13307 is used in an application where the main power goes away but the SENSE voltages they are monitoring stay on because of a SuperCap for 5-10ms.

 

     QUESTION:  Is it safe to have voltages present on SENSE1, SENSE2 and SENSE3 when no voltage is applied to the VDD pin 8?

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