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How PF1550 can discharge lithium battery only when VBUSIN is lost?

Question asked by Anthony Loiseau on Jun 11, 2019
Latest reply on Jun 20, 2019 by G.w. Sun

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.

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