We have a design with a PF1550 PMIC. System is powered by a main power feeding VBUSIN almost permanently and a rescue lithium-ion battery. Our goal is to keep our rescue battery charged in case main power is lost, in order to improve power-cut autonomy. For this reason, we want PMIC to use VBUSIN first, and VBATT only when VBUSIN is lost or weak.
But when our board is powered by both main-power and a charged rescue battery in our standard configuration (CHG_OPER[1:0] = 2), both are actually used to power the system shortening our power-cut autonomy. Worst, this also occurs when we stop the charger (CHG_OPER[1:0]=1) (we must do it explicitly in a few cases to avoid any charge above +45°C otherwise we do not pass certifications). In this second case our rescue battery appears to obviously empty itself.
Does PF1550 features an option to not use lithium-ion source when VBUSIN source is available? I fail to find it.