This paper proposes a digital battery management unit (BMU) with built-in resistance (BIR) compensation and accidental mutation protection (AMP) techniques to achieve fast and accurate charging, which applied in LDO-based charger. The digital compensation dynamically estimates the BIR. The battery can get fully charged with large rated charging current in pulsed constant current (PCC) mode and effectively reduced the charging time. AMP calibrates the mutate messages automatically to deal with some unexpected situations and guarantee the steady operation for the compensation module. The BMU is fabricated in 28 nm CMOS, occupies 0.014 mm of silicon area. Experimental results show that 73.3% charging time is reduced with 1.5A charging current. The power consumption of the digital chip is 59.1 μW.