Power Switch of Multiple Voltage level

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fredhdx573

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Dear all experts,
I am designing a power switch that can switch between VDDA_IN(direct power supply, 1.8V-3.3V) and VBAT(battery power, 1.8V-3.3V).
My problem is that the switch of VBAT cannot completely turn off if VDDA_IN is higher than VBAT (as below picture).


Could you please advise me some ideas?

Regards
 
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You are posting in the IC design section. This implies that transistor bulk nodes must be considered, please show a complete schematic. If P2 bulk is isolated or at highest positive potential, it's sufficient to raise P2 gate voltage to 3.3 V to avoid back current to VBAT.
 

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Thank you for your feedback.


To simplify the discussion, let's temporarily ignore the bulk connection. Based on your advice, we need to determine the maximum voltage of VDDA_IN and VBAT at the gate of P2.


What would be the best approach to achieve this? Would designing a comparator be necessary?
 

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mosfet is symetrica element from both sides of S&D. remove the sign of triangle from S terminal and analyse your circuit in unwanted condition, then you will find the answer!
 

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