I am using the LTC4353 in the configuration shown in the attached image. My application requires that the AUX voltage be higher initially than the MAIN voltage so I would like to disable the AUX current path until the main voltage drops below 9V. I expect M2 to be disabled until the MAIN voltage drops below about 9V when the output of the divider should be roughly <0.6V. This is not happening currently, the AUX supply is enabled when the circuit is powered via 11.5V and 12.3V. Gate2 appears enabled below 0.8V. Not until I turn the main supply up to 12V or so is it disabled. I may be missing something very simple but it is essentially recreating the Typical Application circuit on page 11 of the datasheet, only modifying the input voltages and discretes to match.
Please note that there is a parallel current path through the inherent MOSFET body diode even if the MOSFET channel is turned off by driving its gate low. When MAIN = 11.5V and AUX = 12.3V, the output…
Please note that there is a parallel current path through the inherent MOSFET body diode even if the MOSFET channel is turned off by driving its gate low. When MAIN = 11.5V and AUX = 12.3V, the output will be powered through M2 body diode to 12.3V – 0.7V = 11.6V (roughly). And M1 will be turned off since it sees -0.1V reverse voltage. The datasheet circuit works because those are 3.3V supplies and it’ll work if the difference between them is less than a diode voltage. For your application, please use the 2-channel prioritizer LTC4418: http://www.analog.com/LTC4418