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LTC4353 secondary input voltage drop

I'm experiencing a strange behaviour on a board where I'm using LTC4353 as a "12V Main and Auxiliary Supply Diode-OR" . The circuit I'm working on is depicted below (it's pretty the same circuit found on page 11 of the original datasheet)

Vref value is provided trough a voltage divider:

Testing it I found that it correctly switch between power sources around 9V but while the main source (+12V) is correctly feed into +12P output the secondary (+BATT) is dropping 0.6V..... I don't think this's a correct behaviour but I cannot understand what's the origin ... probably Q1 is not saturating and this lead to some voltage drop but why?

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  • You are right about Q1 not saturating and that is happening because you have connected a Vref signal on EN2 pin. High signal on EN2 will switch the FET at the Gate2 pin which is Q1 in this case. Since Vref is always present there as long as 12V main supply is there, Q1 will never turn on. What is +Batt voltage?

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  • You are right about Q1 not saturating and that is happening because you have connected a Vref signal on EN2 pin. High signal on EN2 will switch the FET at the Gate2 pin which is Q1 in this case. Since Vref is always present there as long as 12V main supply is there, Q1 will never turn on. What is +Batt voltage?

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