Dual batteries in series, hardware design

Please pay attention to the high voltage input scheme （ For example, two batteries are connected in series ）： because Vbat_sense Input voltage limit , Therefore, two are usually used externally 100K The resistor divides the voltage and inputs it to PMU Of Vbat_sense, When there is no charger The voltage detection is basically accurate , So now Vbat_sense stay PMU Internal high resistance state . But actually Vbat_sense Pin in PMU Multiple modules are internally connected ：AUXADC、FGU、OVP、BC1.2、CHARGER etc. , When VCHG It works （>3.3V） Will open after charger And so on VBAT_SENSE The input impedance is significantly reduced ,charger modular （SC2720=SC2721=175K、UMP510G=91K）, If you use 2 individual 100K The resistor divides the voltage to Vbat_sense, The voltage will be detected inaccurately , It is necessary to divide the voltage with resistance and then apply voltage follower for isolation Vbat_sense, solve Vbat_sense The impedance affects the partial voltage ratio . See attachment for example circuit .