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?