I'm searching for a simple solution for a prioritized power path controller to maintain a system supply line through a rechargable battery when the main supply fails.
My goal is to make the cheapest solution. During a long searching on the internet I came accross Ti's design Dual Power Path Multiplexer Reference Design. It uses a voltage window comparator and two couples of back-to-back mosfet for the changeover.
I studied the circuit (Page 8, Figure 4). carefully and I can see a basic problem here. Considering the secondary rail a Li-ion battery 3.7V and the primary rail with a significant greater voltage, for example >5V or >12V. In that case, when the primary rail fails, after the switchover and exactly after the Q1 is fully on (lowest Rds) the battery will see a charged capacitor (C1) with a primary's rail voltage, because when the mosfet is on it does allow the flowing of reverse current. If the load's current is very low, the Capacitor on the load will not discharge enough during the switchover and that remaining amount of voltage may cause damage to the battery.
I found that the problem is solved by ideal diode controllers or ORing controller but I wasn't able to find anything reasonable cheap. In addition, my circuit (load) demands current above 2.5A. Unfortunately, some embedded and cheap TI's chip, are capable to handle maximum 2A.
The TI's schematic above, does not implement any solution for reverse current blocking while the mosfets are on.
