There are two LDO internal the MAXM17537.The VCC is powered by INLDO if EN/UVLO is higher than 0.8V after start-up. The VCC is powered by EXTVCC when VCC is higher than its threshold and EXVCC is higher than 4.7V. Only one of the two LDOs could power VCC. When VCC is powered by EXTVCC, the power loss is low and efficiency is high as the voltages between EXTVCC and VCC is small.